@misc{RossiBargendeKulzeretal., author = {Rossi, Edoardo and Bargende, Michael and Kulzer, Andr{\´e} Casal and Chiodi, Marco and Massoud, Ehab and Shrestha, Krishna Prasad and Mauß, Fabian}, title = {Analysis of the applicability of Water Injection in Combination with an eFuel for Knock Mitigation and Improved Engine Efficiency}, series = {SAE Technical Paper}, journal = {SAE Technical Paper}, issn = {2688-3627}, doi = {10.4271/2022-37-0019}, abstract = {The development of future gasoline engines is dominated by the study of new technologies aimed at reducing the engine negative environmental impact and increase its thermal efficiency. One common trend is to develop smaller engines able to operate in stoichiometric conditions across the whole engine map for better efficiency, lower fuel consumption, and optimal conversion rate of the three-way catalyst (TWC). Water injection is one promising technique, as it significantly reduces the engine knock tendency and avoids fuel enrichment for exhaust temperature mitigation at high power operation. With the focus on reducing the carbon footprint of the automotive sector, another vital topic of research is the investigation of new alternative CO2-neutral fuels or so-called eFuels. Several studies have already shown how these new synthetic fuels can be produced by exploiting renewable energy sources and can significantly reduce engine emissions. This work is part of the FVV project number 1367, "Water Injection in Spark-Ignition Engines II", which investigates the coexistence of two different engine technologies that heads towards the same direction of sustainability of the internal combustion engine: water injection and eFuels. The goal is to assess the advantages that the adoption of an eFuel in combination with water injection strategies can bring, with respect to the same strategies applied in combination with commercial gasoline. Several water injection strategies, including direct water injection, indirect water injection, injection timing, and pressure variations, are considered for a better understanding of the benefits brought by the combination of an eFuel with water injection. For this purpose, experimental tests and 3D-CFD engine simulations have been performed. The physical properties of the investigated eFuel have been experimentally measured for accurate modelling in the simulation environment, and the thermodynamic properties have been evaluated utilizing detailed chemistry calculations.}, language = {en} } @misc{DongAulGregoireetal., author = {Dong, Shijun and Aul, Christopher and Gregoire, Claire and Cooper, Sean P. and Mathieu, Olivier and Petersen, Eric L. and Rodriguez, Jose and Mauß, Fabian and Wagnon, Scott W. and Kukkadapu, Goutham and Pitz, William J. and Curran, Henry J.}, title = {A comprehensive experimental and kinetic modeling study of 1-hexene}, series = {Combustion and Flame}, volume = {232}, journal = {Combustion and Flame}, issn = {1556-2921}, doi = {10.1016/j.combustflame.2021.111516}, abstract = {It is important to understand the low-temperature chemistry of 1-hexene as it is used as a representative alkene component in gasoline surrogate fuels. Ignition delay times (IDTs) of 1-hexene measured in rapid compression machines (RCMs) can be used to validate its low-temperature chemistry. However, volume history profiles are not available for published RCM IDT data. This has restricted the validation of the low-temperature chemistry of 1-hexene at engine-relevant conditions (i.e. at low temperatures and high pressures). Thus, new RCM IDT data with associated volume history profiles are needed. In this study, both an RCM and a high-pressure shock tube (ST) are employed to measure IDTs of 1-hexene at equivalence ratios of 0.5, 1.0 and 2.0 in 'air' and at pressures of 15 and 30 atm. A cool-flame (first stage) and total (second stage) ignition was observed in the RCM experiments. Moreover, carbon monoxide and water versus time histories produced during 1-hexene oxidation at highly diluted conditions were measured in a ST. A new detailed chemical kinetic model describing 1-hexene oxidation is proposed and validated using these new measured data together with various experimental data available in the literature. The kinetic model can predict well the auto-ignition behavior and oxidation processes of 1-hexene at various conditions. The rate constants and branching ratio for hydroxyl radical addition to the double bond of 1-hexene are particularly important and discussed based on the experimental and theoretically calculated results from previous studies as well as validation results from jet-stirred reactor (JSR) species profiles. Flux and sensitivity analyses are performed to determine the important reaction classes for 1-hexene oxidation and show that the reactions associated with hydroxy radical addition to the double bond contribute most to the low-temperature reactivity of 1-hexene. In the negative temperature coefficient (NTC) regime, the isomerization of hexenyl-peroxy radicals promotes fuel reactivity due to its associated chain branching pathways.}, language = {en} } @misc{MatriscianoFrankenGonzalezMestreetal., author = {Matrisciano, Andrea and Franken, Tim and Gonzalez Mestre, Laura Catalina and Borg, Anders and Mauß, Fabian}, title = {Development of a Computationally Efficient Tabulated Chemistry Solver for Internal Combustion Engine Optimization Using Stochastic Reactor Models}, series = {Applied Sciences}, volume = {10}, journal = {Applied Sciences}, number = {24}, issn = {2076-3417}, doi = {10.3390/app10248979}, abstract = {The use of chemical kinetic mechanisms in computer aided engineering tools for internal combustion engine simulations is of high importance for studying and predicting pollutant formation of conventional and alternative fuels. However, usage of complex reaction schemes is accompanied by high computational cost in 0-D, 1-D and 3-D computational fluid dynamics frameworks. The present work aims to address this challenge and allow broader deployment of detailed chemistry-based simulations, such as in multi-objective engine optimization campaigns. A fast-running tabulated chemistry solver coupled to a 0-D probability density function-based approach for the modelling of compression and spark ignition engine combustion is proposed. A stochastic reactor engine model has been extended with a progress variable-based framework, allowing the use of pre-calculated auto-ignition tables instead of solving the chemical reactions on-the-fly. As a first validation step, the tabulated chemistry-based solver is assessed against the online chemistry solver under constant pressure reactor conditions. Secondly, performance and accuracy targets of the progress variable-based solver are verified using stochastic reactor models under compression and spark ignition engine conditions. Detailed multicomponent mechanisms comprising up to 475 species are employed in both the tabulated and online chemistry simulation campaigns. The proposed progress variable-based solver proved to be in good agreement with the detailed online chemistry one in terms of combustion performance as well as engine-out emission predictions (CO, CO2, NO and unburned hydrocarbons). Concerning computational performances, the newly proposed solver delivers remarkable speed-ups (up to four orders of magnitude) when compared to the online chemistry simulations. In turn, the new solver allows the stochastic reactor model to be computationally competitive with much lower order modeling approaches (i.e., Vibe-based models). It also makes the stochastic reactor model a feasible computer aided engineering framework of choice for multi-objective engine optimization campaigns.}, language = {en} } @misc{FrankenSeidelGonzalezMestreetal., author = {Franken, Tim and Seidel, Lars and Gonzalez Mestre, Laura Catalina and Shrestha, Krishna Prasad and Matrisciano, Andrea and Mauss, Fabian}, title = {Assessment of Auto-Ignition Tendency of Gasoline, Methanol, Toluene and Hydrogen Fuel Blends in Spark Ignition Engines}, series = {THIESEL 2020 Conference on Thermo-and Fluid Dynamic Processes in Direct Injection Engines}, journal = {THIESEL 2020 Conference on Thermo-and Fluid Dynamic Processes in Direct Injection Engines}, pages = {23}, abstract = {State of the art spark ignited gasoline engines achieve thermal efficiencies above 46 \% e.g. due to friction optimized crank trains, high in-cylinder tumble flow and direct fuel injection. Further improvements of thermal efficiency are expected from lean combustion, higher compression ratio and new knock-resistant fuel blends. One of the limitations to these improvements are set by the autoignition in the end gas, which can develop to knocking combustion and severely damage the internal combustion engine. The auto-ignition is enhanced by high cylinder gas temperatures and reactive species in the end gas composition. Quasi-dimensional Stochastic Reactor Model simulations with detailed chemistry allow to consider the thermochemistry properties of surrogates and complex end gas compositions. Based on the detailed reaction scheme and surrogate model, an innovative tabulated chemistry approach is utilized to generate dual-fuel laminar flame speed and combustion chemistry look-up tables. This reduces the simulation duration to seconds per cycle, while the loss in accuracy compared to solving the chemistry "online" is marginal. The auto-ignition events predicted by the tabulated chemistry simulation are evaluated using the Detonation Diagram developed by Bradley and co-workers. This advanced methodology for quasi-dimensional models evaluates the resonance between the shock wave and reactionfront velocity from auto-ignition in the end gas and determines if it is a harmful developing detonation or normal deflagration. The aim of this work is to evaluate the auto-ignition characteristics of different fuel blends. The Stochastic Reactor Model with tabulated chemistry is applied to perform a numerical analysis of the autoignition of the fuel blends and operating conditions. Experimental measurements of a single cylinder research engine operated with RON95 E10 fuel are used to train and validate the simulation model. The RON95 E10 fuel is blended with Methanol, Hydrogen and Toluene. The knock tendency based on the evaluation of auto-ignition events of the different fuel blends are analysed for three operating points at 1500 rpm 15 bar IMEP, 2000 rpm 20 bar IMEP and 2500 rpm 15 bar IMEP with advanced spark timings.}, language = {en} } @misc{MatriscianoNetzerWerneretal., author = {Matrisciano, Andrea and Netzer, Corinna and Werner, Adina and Borg, Anders and Seidel, Lars and Mauß, Fabian}, title = {A Computationally Efficient Progress Variable Approach for In-Cylinder Combustion and Emissions Simulations}, series = {SAE Technical Paper}, journal = {SAE Technical Paper}, issn = {0148-7191}, doi = {10.4271/2019-24-0011}, abstract = {The use of complex reaction schemes is accompanied by high computational cost in 3D CFD simulations but is particularly important to predict pollutant emissions in internal combustion engine simulations. One solution to tackle this problem is to solve the chemistry prior the CFD run and store the chemistry information in look-up tables. The approach presented combines pre-tabulated progress variable-based source terms for auto-ignition as well as soot and NOx source terms for emission predictions. The method is coupled to the 3D CFD code CONVERGE v2.4 via user-coding and tested over various speed and load passenger-car Diesel engine conditions. This work includes the comparison between the combustion progress variable (CPV) model and the online chemistry solver in CONVERGE 2.4. Both models are compared by means of combustion and emission parameters. A detailed n-decane/α-methyl-naphthalene mechanism, comprising 189 species, is used for both online and tabulated chemistry simulations. The two chemistry solvers show very good agreement between each other and equally predict trends derived experimentally by means of engine performance parameters as well as soot and NOx engine-out emissions. The CPV model shows a factor 8 speed-up in run-time compared to the online chemistry solver without compromising the accuracy of the solution.}, language = {en} } @misc{FrankenDugganMatriscianoetal., author = {Franken, Tim and Duggan, Alexander and Matrisciano, Andrea and Lehtiniemi, Harry and Borg, Anders and Mauß, Fabian}, title = {Multi-Objective Optimization of Fuel Consumption and NO x Emissions with Reliability Analysis Using a Stochastic Reactor Model}, series = {SAE Technical Paper}, journal = {SAE Technical Paper}, issn = {0148-7191}, doi = {10.4271/2019-01-1173}, abstract = {The introduction of a physics-based zero-dimensional stochastic reactor model combined with tabulated chemistry enables the simulation-supported development of future compression-ignited engines. The stochastic reactor model mimics mixture and temperature inhomogeneities induced by turbulence, direct injection and heat transfer. Thus, it is possible to improve the prediction of NOx emissions compared to common mean-value models. To reduce the number of designs to be evaluated during the simulation-based multi-objective optimization, genetic algorithms are proven to be an effective tool. Based on an initial set of designs, the algorithm aims to evolve the designs to find the best parameters for the given constraints and objectives. The extension by response surface models improves the prediction of the best possible Pareto Front, while the time of optimization is kept low. This work presents a novel methodology to couple the stochastic reactor model and the Non-dominated Sorting Genetic Algorithm. First, the stochastic reactor model is calibrated for 10 low, medium and high load operating points at various engine speeds. Second, each operating point is optimized to find the lowest fuel consumption and specific NOx emissions. The optimization input parameters are the temperature at intake valve closure, the compression ratio, the start of injection, the injection pressure and exhaust gas recirculation rate. Additionally, it is ensured that the maximum peak cylinder pressure and turbine inlet temperature are not exceeded. This enables a safe operation of the engine and exhaust aftertreatment system under the optimized conditions. Subsequently, a reliability analysis is performed to estimate the effect of off-nominal conditions on the objectives and constraints. The novel multi-objective optimization methodology has proven to deliver reasonable results. The zero-dimensional stochastic reactor model with tabulated chemistry is a fast running physics-based model that allow to run large optimization problems in a short amount of time. The combination with the reliability analysis also strengthens the confidence in the simulation-based optimized engine operation parameters.}, language = {en} } @misc{KurapatiBorgSeideletal., author = {Kurapati, Vinaykumar Reddy and Borg, Anders and Seidel, Lars and Mauß, Fabian}, title = {Fast CFD Diesel engine modelling using the 1-Dimentional SprayLet approach}, series = {SAE Technical Paper}, journal = {SAE Technical Paper}, number = {2024-01-2684}, issn = {0148-7191}, abstract = {In the SAE article 2023-24-0083: SprayLet: One-dimensional interactive cross-sectionally averaged spray model, we formulatet a one-dimensional Spray model in interaction with the surrounding gas phase. We could demonstrate, that the model predicted liquid and gaseous penetration length in good aggreement with ECN spray experiments. In this paper we use this model in engine CFD (CONVERGE CFD) and demonstrate a strong reduction in CPU time (50\%). We can show a strong decrease in grid dependency, which allows a further reduction of CPU time (90\%). We will present engine CFD simulations, comparing detailed spray with SpayLet simulations. This includes pressure traces, heat release, and emissions.}, language = {en} } @misc{KurapatiBorgSeideletal., author = {Kurapati, Vinaykumar Reddy and Borg, Anders and Seidel, Lars and Mauß, Fabian}, title = {SprayLet: One-Dimensional Interactive Cross-Sectionally Averaged Spray Model}, series = {SAE Technical Paper}, journal = {SAE Technical Paper}, issn = {0148-7191}, doi = {10.4271/2023-24-0083}, abstract = {Spray modeling is among the main aspects of mixture formation and combustion in internal combustion engines. It plays a major role in pollutant formation and energy efficiency although adequate modeling is still under development. Strong grid dependence is observed in the droplet-based stochastic spray model commonly used. As an alternative, an interactive model called 'SprayLet' is being developed for spray simulations based on one-dimensional integrated equations for the gas and liquid phases, resulting from cross-sectionally averaging of multi-dimensional transport equations to improve statistical convergence. The formulated one-dimensional cross-section averaged system is solved independently of the CFD program to provide source terms for mass, momentum and heat transfer between the gas and liquid phases. The transport processes take place in a given spray cone where the nozzle exit is automatically resolved. In the 1D program, the conservation equations are for droplet diameter, droplet temperature, as well as for continuity and momentum of the liquid and the gaseous phase are solved. The source terms between the phases are conservatively embedded into the spray region of the CFD program. In CFD program, the transport equations are solved for gas phase only. The SprayLet model is validated using standard Sandia sprays by comparing penetration lengths and fuel mixture fractions with experimental data.}, language = {en} } @misc{MannaSabiaShresthaetal., author = {Manna, Maria Virginia and Sabia, Pino and Shrestha, Krishna Prasad and Seidel, Lars and Ragucci, Raffaele and Mauß, Fabian and De Joannon, Mara}, title = {NH3NO interaction at low-temperatures: an experimental and modeling study}, series = {Proceedings of the Combustion Institute}, volume = {39}, journal = {Proceedings of the Combustion Institute}, number = {1}, issn = {1873-2704}, doi = {10.1016/j.proci.2022.09.027}, pages = {775 -- 784}, abstract = {The present work provides new insight into NH3single bondNO interaction under low-temperature conditions. The oxidation process of neat NH3 and NH3 doped with NO (450, 800 ppm) was experimentally investigated in a Jet Stirred Flow Reactor at atmospheric pressure for the temperature range 900-1350 K. Results showed NO concentration is entirely controlled by DeNOx reactions in the temperature range 1100-1250 K, while NH3single bondNO interaction does not develop through a sensitizing NO effect, for these operating conditions. A detailed kinetic model was developed by systematically updating rate constants of controlling reactions and declaring new reactions for N2H2 isomers (cis and trans). The proposed mechanism well captures target species as NO and H2 profiles. For NH3single bondNO mixtures, NO profiles were properly reproduced through updated DeNOx chemistry, while NH2 recombination reactions were found to be essential for predicting the formation of H2. The role of ammonia as a third-body species is implemented in the updated mechanism, with remarkable effects on species predictions. For neat NH3 mixture, the reaction H+O2(+M)=HO2(+M) was crucial to predict NO formation via the reaction NH2+HO2double bondH2NO+OH.}, language = {en} } @misc{MantePrehnTheileetal., author = {Mante, Till and Prehn, Sascha and Theile, Martin and Seidel, Lars and Mestre, Laura and Buchholz, Bert and Mauß, Fabian}, title = {Investigation of An Ammonia Diesel Dual-Fuel Combustion Process on a Heavy-Duty Single Cylinder Research Engine for the Development of Suitable Simulation Tools for Maritime Applications}, series = {Heavy-Duty-, On- und Off-Highway-Motoren 2022 : Stand der Energiewende im Heavy-Duty-Bereich}, journal = {Heavy-Duty-, On- und Off-Highway-Motoren 2022 : Stand der Energiewende im Heavy-Duty-Bereich}, editor = {Heintzel, Alexander}, publisher = {Springer Vieweg}, address = {Wiesbaden}, isbn = {978-3-658-41477-1}, doi = {10.1007/978-3-658-41477-1_3}, pages = {24 -- 39}, abstract = {This paper discusses the adaption of a single cylinder research engine for a retrofit application with an ammonia diesel dual-fuel combustion process and the build of an ammonia fuel system. The gaseous ammonia will be injected in the air intake pipe and the premixed ammonia air mixture will enter the combustion chamber. The diesel injection is carried out via a high-pressure common rail system. All relevant parameters can be freely adjusted via a freely programmable control unit. With the help of experimental data from a single cylinder research engine at the chair of piston machines and internal combustion engines of the University of Rostock (LKV), a dual-fuel combustion model based on detailed chemistry will be developed and optimized. This model will be integrated in a full research engine model, which ensures the best possible representation of the real engine. The combustion model is being developed by LOGE Deutschland GmbH. The full research engine model is developed by FVTR GmbH. The analysis of the combustion process starts with pure diesel operating points and is successively substituted by ammonia in the course of the measurement campaigns. Both the combustion characteristics are relevant, as they significantly influence the resulting performance and engine operation, as well as the exhaust emissions, as the carbon emissions can be reduced, but the nitrogen oxides and ammonia slip increase significantly in relevance due to the ammonia. The results obtained will be used to derive initial recommendations for action and to estimate the potential for application in the inland waterway shipping. In addition, the development of the systematic simulation tools covers a broad spectrum of research questions and aims to increase the efficiency of the necessary R\&D.}, language = {en} } @misc{Turquandd'AuzayShapiroProuvieretal., author = {Turquand d'Auzay, Charles and Shapiro, Evgeniy and Prouvier, Matthieu and Winkler, Axel and Seidel, Lars and Borg, Anders and Mauß, Fabian}, title = {Evaluation of Fast Detailed Kinetics Calibration Methodology for 3D CFD Simulations of Spray Combustion}, series = {SAE Technical Paper}, journal = {SAE Technical Paper}, number = {2022-01-1042}, issn = {0148-7191}, doi = {10.4271/2022-01-1042}, abstract = {Meeting strict current and future emissions legislation necessitates development of computational tools capable of predicting the behaviour of combustion and emissions with an accuracy sufficient to make correct design decisions while keeping computational cost of the simulations amenable for large-scale design space exploration. While detailed kinetics modelling is increasingly seen as a necessity for accurate simulations, the computational cost can be often prohibitive, prompting interest in simplified approaches allowing fast simulation of reduced mechanisms at coarse grid resolutions appropriate for internal combustion engine simulations in design context. In this study we present a simplified Well-stirred Reactor (WSR) implementation coupled with 3D CFD Ricardo VECTIS solver. A detailed evaluation of benchmark ECN spray problem is presented demonstrating that a single point calibration of such a model using a bulk reaction multiplier approach can provide correct representation of the solution across a wide range of temperatures on grid sizes typically employed for RANS internal combustion engine simulations with tabulated kinetics or zonal combustion models.}, language = {en} } @misc{VanTreekLubranoLavaderaSeideletal., author = {Van Treek, Lisa and Lubrano Lavadera, Marco and Seidel, Lars and Mauß, Fabian and Konnov, Alexander A.}, title = {Experimental and modelling study of laminar burning velocity of aqueous ethanol}, series = {Fuel}, volume = {257}, journal = {Fuel}, issn = {1873-7153}, doi = {10.1016/j.fuel.2019.116069}, abstract = {Laminar burning velocities of ethanol-water-air mixtures have been determined using the heat flux method. Aqueous ethanol contained 0-40\% of water by mole fraction. Laminar premixed flat flames were stabilized on a perforated burner under adiabatic conditions for the equivalence ratio range from 0.7 to 1.4. Burning velocity measurements were performed for the initial gas temperature of 358 K and at atmospheric pressure. The results for ethanol-air flames are in good agreement with the previous data obtained using the same heat flux method. The present and literature experimental data were compared against predictions using four different kinetic models. All models show uniform behaviour over the range of ethanol dilution by water covered in the present study. However, model predictions significantly diverge from the experimental data obtained in spherical flames. To quantify the effect of dilution on the laminar burning velocity, an empirical dimensionless correlation has been derived from the experimental data and predictions of the models tested. Further numerical analyses were performed to identify the effects of water addition on laminar burning velocities. Results suggested that water strongly interacts with the H2/O2 and C1 oxidation/recombination routes.}, language = {en} } @misc{HilbigMalliotakisSeideletal., author = {Hilbig, Martin and Malliotakis, Zisis and Seidel, Lars and Vourliotakis, George and Keramiotis, Christos and Mauß, Fabian and Founti, Maria}, title = {The effect of base chemistry choice in a generated n-hexane oxidation model using an automated mechanism generator}, series = {International Journal of Chemical Kinetics}, volume = {51}, journal = {International Journal of Chemical Kinetics}, number = {10}, issn = {1097-4601}, doi = {10.1002/kin.21309}, pages = {786 -- 798}, abstract = {The present study describes the utilization of a reaction mechanism generator for the development of chemical kinetic models. The aim of the investigation is twofold. The in-house developed mechanism generator is updated with reaction classes reported in the literature, and the effect of the lower hydrocarbon chemistry, that is, base chemistry, on the generation process is assessed. For this purpose, the algorithm is implemented on two different base chemistry mechanisms, that have previously been validated against a different range of hydrocarbons, that is, the mechanisms of the groups coauthoring the study. n-Hexane has been used as a modeling target due to its important role in combustion studies as a surrogate for engine and aviation applications. The steps of the generation process are given in detail as this is the first time the current algorithm is utilized. The two generated mechanisms are compared against speciation data, ignition delay times, and flame velocities from the literature. The overall agreement of the generated mechanisms is satisfying; discrepancies exist in the negative temperature coefficient regime. Reaction path analysis and sensitivity analysis were performed, revealing the reactions that cause the different mechanism performance. Among others, the study reveals that the generated schemes pose a fast and adequate alternative to literature mechanisms; it is however evident that the latter may include more detailed reaction paths and are therefore superior in terms of validation.}, language = {en} } @misc{RichterGuentherMauss, author = {Richter, Jana and G{\"u}nther, Vivien and Mauß, Fabian}, title = {Reaction mechanism development and investigation on the convergence influence in a 1D catalyst model for a γ-alumina stabilized three-way catalyst}, series = {The Proceedings of the International symposium on diagnostics and modeling of combustion in internal combustion engines}, journal = {The Proceedings of the International symposium on diagnostics and modeling of combustion in internal combustion engines}, issn = {2424-2918}, doi = {10.1299/jmsesdm.2022.10.A10-3}, abstract = {Accurate and computational cost-effective modeling tools for the optimization of processes and devices of all kinds are needed in nearly all scientific fields. While experimental optimization entails high expenses in terms of cost and time virtual optimization may be a promising alternative. In this work, the suitability and accuracy of a 1D heterogeneous catalytic model is investigated. First, the influence of cell discretization and residence time on the convergence in a 1D catalyst model are investigated. Second, the catalyst model is investigated and validated with use of a stoichiometric steady state three-way catalyst experiment. With the help of these investigations the reaction mechanism is further developed and new reaction rates for two reactions are presented. The modeling results are compared to a 2D simulation approach in terms of computational time and catalyst conversion behavior. The presented model is capable to capture the experimental results with a drastically reduced computational time in comparison to the 2D simulation presented in literature.}, language = {en} } @misc{MaiBuiNhungetal., author = {Mai, Tam V.-T. and Bui, Thanh Q. and Nhung, Nguyen Thi Ai and Quy, Phan Tu and Shrestha, Krishna Prasad and Mauß, Fabian and Giri, Binod Raj and Huynh, Lam Kim}, title = {An Ab Initio RRKM-Based Master Equation Study for Kinetics of OH-Initiated Oxidation of 2-Methyltetrahydrofuran and Its Implications in Kinetic Modeling}, series = {Energies}, volume = {16}, journal = {Energies}, number = {9}, issn = {1996-1073}, doi = {10.3390/en16093730}, abstract = {Cyclic ethers (CEs) can be promising future biofuel candidates. Most CEs possess physico-chemical and combustion indicators comparable to conventional fuels, making them suitable for internal combustion engines. This work computationally investigates the kinetic behaviors of hydrogen abstraction from 2-methyl tetrahydrofuran (2MTHF), one of the promising CEs, by hydroxyl radicals under combustion and atmospheric relevant conditions. The various reaction pathways were explored using the CCSD(T)/cc-pVTZ//M06-2X/aug-cc-pVTZ level of theory. The Rice-Ramsperger-Kassel-Marcus-based master equation (RRKM-ME) rate model, including treatments for hindered internal rotation and tunneling, was employed to describe time-dependent species profiles and pressure and temperature-dependent rate coefficients. Our kinetic model revealed that the H-abstraction proceeds via an addition-elimination mechanism forming reaction complexes at both the entrance and exit channels. Eight different reaction channels yielding five radical products were located. The reaction exhibited complex kinetics yielding a U-shaped Arrhenius behavior. An unusual occurrence of negative temperature dependence was observed at low temperatures, owing to the negative barrier height for the hydrogen abstraction reaction from the C-H bond at the vicinity of the O-atom. A shift in the reaction mechanism was observed with the dominance of the abstraction at Cα-H of 2MTHF ring (causing negative-T dependence) and at CH3 (positive-T dependence) at low and high temperatures, respectively. Interestingly, the pressure effect was observed at low temperatures, revealing the kinetic significance of the pre-reaction complex. Under atmospheric pressure, our theoretical rate coefficients showed excellent agreement with the available literature data. Our model nicely captured the negative temperature-dependent behaviors at low temperatures. Our predicted global rate coefficients can be expressed as k (T, 760 Torr) = 3.55 × 101 × T-4.72 × exp [-340.0 K/T] + 8.21 × 10-23 × T3.49 × exp [918.8 K/T] (cm3/molecule/s). Our work provides a detailed kinetic picture of the OH-initiated oxidation kinetics of 2MTHF. Hence, this information is useful for building a kinetic me chanism for methylated cyclic ethers.}, language = {en} } @misc{SiddareddyFrankenPasternaketal., author = {Siddareddy, Reddy Babu and Franken, Tim and Pasternak, Michal and Leon de Syniawa, Larisa and Oder, Johannes and Rottengruber, Hermann and Mauß, Fabian}, title = {Real-Time Simulation of CNG Engine and After-Treatment System Cold Start. Part 1: Transient Engine-Out Emission Prediction Using a Stochastic Reactor Model}, series = {SAE Technical Paper}, journal = {SAE Technical Paper}, issn = {2688-3627}, doi = {10.4271/2023-01-0183}, abstract = {During cold start of natural gas engines, increased methane and formaldehyde emissions can be released due to flame quenching on cold cylinder walls, misfiring and the catalyst not being fully active at low temperatures. Euro 6 legislation does not regulate methane and formaldehyde emissions. New limits for these two pollutants have been proposed by CLOVE consortium for Euro 7 scenarios. These proposals indicate tougher requirements for aftertreatment systems of natural gas engines. In the present study, a zero-dimensional model for real-time engine-out emission prediction for transient engine cold start is presented. The model incorporates the stochastic reactor model for spark ignition engines and tabulated chemistry. The tabulated chemistry approach allows to account for the physical and chemical properties of natural gas fuels in detail by using a-priori generated laminar flame speed and combustion chemistry look-up tables. The turbulence-chemistry interaction within the combustion chamber is predicted using a K-k turbulence model. The optimum turbulence model parameters are trained by matching the experimental cylinder pressure and engine-out emissions of nine steady-state operating points. Subsequently, the trained engine model is applied for predicting engine-out emissions of a WLTP passenger car engine cold start. The predicted engine-out emissions comprise nitrogen oxide, carbon monoxide, carbon dioxide, unburnt methane, formaldehyde, and hydrogen. The simulation results are validated by comparing to transient engine measurements at different ambient temperatures (-7°C, 0°C, 8°C and 20°C). Additionally, the sensitivity of engine-out emissions towards air-fuel-ratio (λ=1.0 and λ=1.3) and natural gas quality (H-Gas and L-Gas) is investigated.}, language = {en} } @misc{LeondeSyniawaSiddareddyOderetal., author = {Leon de Syniawa, Larisa and Siddareddy, Reddy Babu and Oder, Johannes and Franken, Tim and G{\"u}nther, Vivien and Rottengruber, Hermann and Mauß, Fabian}, title = {Real-Time Simulation of CNG Engine and After-Treatment System Cold Start. Part 2: Tail-Pipe Emissions Prediction Using a Detailed Chemistry Based MOC Model}, series = {SAE Technical Report}, journal = {SAE Technical Report}, issn = {2688-3627}, doi = {10.4271/2023-01-0364}, abstract = {In contrast to the currently primarily used liquid fuels (diesel and gasoline), methane (CH4) as a fuel offers a high potential for a significant reduction of greenhouse gas emissions (GHG). This advantage can only be used if tailpipe CH4 emissions are reduced to a minimum, since the GHG impact of CH4 in the atmosphere is higher than that of carbon dioxide (CO2). Three-way catalysts (TWC - stoichiometric combustion) and methane oxidation catalysts (MOC - lean combustion) can be used for post-engine CH4 oxidation. Both technologies allow for a nearly complete CH4 conversion to CO2 and water at sufficiently high exhaust temperatures (above the light-off temperature of the catalysts). However, CH4 combustion is facing a huge challenge with the planned introduction of Euro VII emissions standard, where stricter CH4 emission limits and a decrease of the cold start starting temperatures are discussed. The aim of the present study is to develop a reliable kinetic catalyst model for MOC conversion prediction in order to optimize the catalyst design in function of engine operation conditions, by combining the outputs from the predicted transient engine simulations as inputs to the catalyst model. Model development and training has been performed using experimental engine test bench data at stoichiometric conditions as well as engine simulation data and is able to reliably predict the major emissions under a broad range of operating conditions. Cold start (-7°C and +20°C) experiments were performed for a simplified worldwide light vehicle test procedure (WLTP) driving cycle using a prototype gas engine together with a MOC. For the catalyst simulations, a 1-D catalytic converter model was used. The model includes detailed gas and surface chemistry that are computed together with catalyst heat up. In a further step, a virtual transient engine cold start cycle is combined with the MOC model to predict tail-pipe emissions at transient operating conditions. This method allows to perform detailed emission investigations in an early stage of engine prototype development.}, language = {en} } @misc{RakhiGuentherMauss, author = {Rakhi, Rakhi and G{\"u}nther, Vivien and Mauß, Fabian}, title = {A detailed surface reaction mechanism to investigate oxidation of methane over nickel catalyst}, series = {Proceedings in Applied Mathematics \& Mechanics : PAMM}, volume = {22}, journal = {Proceedings in Applied Mathematics \& Mechanics : PAMM}, number = {1}, issn = {1617-7061}, doi = {10.1002/pamm.202200055}, abstract = {We have developed a kinetically consistent detailed surface reaction mechanism for modeling the oxidation of methane over a nickel-based catalyst. A one-dimensional model, LOGEcat based on the single-channel 1D catalyst model, is used to perform the simulations. The original multi-step reaction mechanism is thermodynamically consistent and consists of 52 reactions. By thermodynamic consistency, we mean that the equilibrium is achieved with the support of the Arrhenius parameters and does not depend on the thermochemistry of the species involved in the considered reactions. The detailed mechanism developed in this investigation contains 26 reversible reactions. These reactions are obtained with the use of the thermochemistry of the species. The study focuses on ensuring kinetic consistency and this is done with the help of thermodynamic analysis by bringing the thermochemistry of the species in play in order to develop a surface reaction mechanism. The new mechanism can be used to understand the other processes, for example, steam- and dry-reforming of methane over nickel, however, the main focus of the paper is to check the performance of the detailed mechanism for catalytic partial oxidation of methane. The applicability of the mechanism is checked for various reactor conditions in terms of parameters such as temperature and pressure by comparing the results with the available reference data. The detailed mechanism developed in this study is able to accurately express oxidation of methane over the nickel catalyst for the considered reactor conditions.}, language = {en} } @misc{RakhiGuentherMauss, author = {Rakhi, Rakhi and G{\"u}nther, Vivien and Mauß, Fabian}, title = {Insights into dry reforming of methane over nickel catalyst using a thermodynamic model}, series = {Reaction Kinetics, Mechanisms and Catalysis}, journal = {Reaction Kinetics, Mechanisms and Catalysis}, issn = {1878-5204}, doi = {10.1007/s11144-023-02426-8}, pages = {14}, abstract = {A thermodynamic model is developed using a one-dimensional model, LOGEcat to understand the dry reforming of methane over nickel-based catalysts. To do so, we have extended our previously developed mechanism (Rakhi and Shrestha in React Kinet, Mech Catal 135:3059-3083, 2022) which contains 21 reversible reactions by adding 5 more reversible reactions and updating the thermochemistry of one intermediate species. The adjusted mechanism contains 26 reversible reactions obtained with the help of thermodynamic analysis. This study focuses on using the thermodynamic model for dry reforming of methane and insights into the reaction pathways and sensitivity analysis for the kinetically consistent surface reaction mechanism. The applicability of the mechanism is examined for reactor conditions in terms of parameters such as temperature by comparing the results with the available reference data. The mechanism is able to accurately express the reforming conditions of methane over the nickel catalyst for complete range of temperature and also provide useful insights into the reaction pathways established with the thermodynamic model.}, language = {en} } @misc{SiddareddyFrankenLeondeSyniawaetal., author = {Siddareddy, Reddy Babu and Franken, Tim and Leon de Syniawa, Larisa and Pasternak, Michal and Prehn, Sascha and Buchholz, Bert and Mauß, Fabian}, title = {Simulation of CNG Engine in Agriculture Vehicles. Part 1: Prediction of Cold Start Engine-Out Emissions Using Tabulated Chemistry and Stochastic Reactor Model}, series = {SAE Technical Paper}, journal = {SAE Technical Paper}, issn = {0148-7191}, doi = {10.4271/2023-24-0006}, abstract = {Worldwide, there is the demand to reduce harmful emissions from non-road vehicles to fulfill European Stage V+ and VI (2022, 2024) emission legislation. The rules require significant reductions in nitrogen oxides (NOx), methane (CH4) and formaldehyde (CH2O) emissions from non-road vehicles. Compressed natural gas (CNG) engines with appropriate exhaust aftertreatment systems such as threeway catalytic converter (TWC) can meet these regulations. An issue remains for reducing emissions during the engine cold start where the CNG engine and TWC yet do not reach their optimum operating conditions. The resulting complexity of engine and catalyst calibration can be efficiently supported by numerical models. Hence, it is required to develop accurate simulation models which can predict cold start emissions. This work presents a real-time engine model for transient engine-out emission prediction using tabulated chemistry for CNG. The engine model is based on a stochastic reactor model (SRM) which describes the in-cylinder processes of spark ignition (SI) engines including large-scale and lowscale turbulence, convective heat transfer, turbulent flame propagation and chemistry. Chemistry is described using a tabulated chemistry model which calculates the major exhaust gas emissions of CNG engines such as CO2, NOx, CO, CH4 and CH2O. By best practice, the engine model parameters are optimized by matching the experimental cylinder pressure and engine-out emissions from steady-state operating points. The engine model is trained for a non-road transient cycle (NRTC) cold start at 25°C ambient temperature and validated for a NRTC cold start at 10°C ambient temperature. The trained model is evaluated regarding their feasibility and accuracy predicting transient engineout emissions.}, language = {en} } @misc{LeondeSyniawaSiddareddyPrehnetal., author = {Leon de Syniawa, Larisa and Siddareddy, Reddy Babu and Prehn, Sascha and G{\"u}nther, Vivien and Franken, Tim and Buchholz, Bert and Mauß, Fabian}, title = {Simulation of CNG Engine in Agriculture Vehicles. Part 2: Coupled Engine and Exhaust Gas Aftertreatment Simulations Using a Detailed TWC Model}, series = {SAE Technical Paper}, journal = {SAE Technical Paper}, issn = {0148-7191}, doi = {10.4271/2023-24-0112}, abstract = {In more or less all aspects of life and in all sectors, there is a generalized global demand to reduce greenhouse gas (GHG) emissions, leading to the tightening and expansion of existing emissions regulations. Currently, non-road engines manufacturers are facing updates such as, among others, US Tier 5 (2028), European Stage V (2019/2020), and China Non-Road Stage IV (in phases between 2023 and 2026). For on-road applications, updates of Euro VII (2025), China VI (2021), and California Low NOx Program (2024) are planned. These new laws demand significant reductions in nitrogen oxides (NOx) and particulate matter (PM) emissions from heavy-duty vehicles. When equipped with an appropriate exhaust aftertreatment system, natural gas engines are a promising technology to meet the new emission standards. Gas engines require an appropriate aftertreatment technology to mitigate additional GHG releases as natural gas engines have challenges with methane (CH4) emissions that have 28 times more global warming potential compared to CO2. Under stoichiometric conditions a three-way catalytic converter (TWC - stoichiometric combustion) can be used to effectively reduce emissions of harmful pollutants such as nitrogen oxides and carbon monoxide (CO) as well as GHG like methane. The aim of the present study is to understand the performance of the catalytic converter in function of the engine operation and coolant temperature in order to optimize the catalyst operating conditions. Different cooling temperatures are chosen as the initial device temperature highly affects the level of warm up emissions such that low coolant temperatures entail high emissions. In order to investigate the catalyst performance, experimental and virtual transient engine emissions are coupled with a TWC model to predict tail-pipe emissions at transient operating conditions. Engine experiments are conducted at two initial engine coolant temperatures (10°C and 25°C) to study the effects on the Non-Road Transient Cycle (NRTC) emissions. Engine simulations of combustion and emissions with acceptable accuracy and with low computational effort are developed using the Stochastic Reactor Model (SRM). Catalyst simulations are performed using a 1D catalytic converter model including detailed gas and surface chemistry. The initial section covers essential aspects including the engine setup, definition of the engine test cycle, and the TWC properties and setup. Subsequently, the study introduces the transient SI-SRM, 1D catalyst model, and kinetic model for the TWC. The TWC model is used for the validation of a NRTC at different coolant temperatures (10°C and 25°C) during engine start. Moving forward, the next section includes the coupling of the TWC model with measured engine emissions. Finally, a virtual engine parameter variation has been performed and coupled with TWC simulations to investigate the performance of the engine beyond the experimental campaign. Various engine operating conditions (lambda variation for this paper) are virtually investigated, and the performance of the engine can be extrapolated. The presented virtual development approach allows comprehensive emission evaluations during the initial stages of engine prototype development}, language = {en} } @misc{DavidAgnewBanaresAlcantaraetal., author = {David, William I. F. and Agnew, Gerry D. and Ba{\~n}ares-Alc{\´a}ntara, Ren{\´e} and Barth, James and Hansen, John Bogild and Br{\´e}quigny, Pierre and De Joannon, Mara and F{\"u}rstenberg Stott, Sofia and F{\"u}rstenberg Stott, Conor and Guati-Rojo, Andrea and Hatzell, Marta and MacFarlane, Douglas R. and Makepeace, Joshua W. and Mastorakos, Epaminondas and Mauß, Fabian and Medford, Andrew and Mounaim-Rousselle, Christine and Nowicki, Duncan A. and Picciani, Mark A. and Postma, Rolf S. and Rouwenhorst, Kevin H. R. and Sabia, Pino and Salmon, Nicholas and Simonov, Alexandr N. and Smith, Collin and Torrente-Murciano, Laura and Valera-Medina, Augustin}, title = {2023 Roadmap on ammonia as a carbon-free fuel}, series = {Journal of Physics: Energy}, volume = {6}, journal = {Journal of Physics: Energy}, number = {2}, issn = {2515-7655}, doi = {10.1088/2515-7655/ad0a3a}, abstract = {The 15 short chapters that form this 2023 ammonia-for-energy roadmap provide a comprehensive assessment of the current worldwide ammonia landscape and the future opportunities and associated challenges facing the use of ammonia, not only in the part that it can play in terms of the future displacement of fossil-fuel reserves towards massive, long-term, carbon-free energy storage and heat and power provision, but also in its broader holistic impacts that touch all three components of the future global food-water-energy nexus.}, language = {en} } @misc{GiriPalaciosThangarajetal., author = {Giri, Binod Raj and Palacios, Manuel Monge and Thangaraj, Ravikumar and Shrestha, Krishna Prasad and Viskolcz, B{\´e}la and Mauss, Fabian and Szőri, Mil{\´a}n}, title = {An Ab initio based OH initiated oxidation kinetics of glycerol carbonate: A promising biofuel component}, series = {Proceedings of the Combustion Institute}, volume = {40}, journal = {Proceedings of the Combustion Institute}, publisher = {Elsevier}, doi = {10.1016/j.proci.2024.105668}, pages = {1 -- 8}, abstract = {The global energy demand is steadily increasing because of the population explosion and economic growth. Fossil fuels supply around 85 \% of global primary energy demand. On one hand, fulfilling the increasing energy demands is a big challenge for the next few decades. On the other hand, the continued burning of fossil fuels leads to higher CO2 emissions, severely impacting global warming. Therefore, the policymakers vow to shift from conventional fuels to renewable resources for economic, environmental, and future energy security reasons. In this context, biofuels from lignocellulosic biomass and/or carbon-neutral fuels produced in the sustainable carbon cycle can close the carbon cycle and reach net zero-carbon emission. Recently, glycerol carbonate has been proposed as a promising fuel or fuel additive for future sustainability. Therefore, we investigated the hydrogen abstraction reactions of glycerol carbonate (GC) by OH radicals using high-level ab initio and variational transition state theory calculations. We mapped out the potential energy surface using the CCSD(T)/cc-pV(D, T)Z//MP2/cc-pVTZ level of theory. We used the ab initio parameters to obtain the site-specific rate coefficients by employing the variational transition state theory. We observed that every hydrogen atom in GC displays a unique reactivity with OH radicals. We derived branching ratio of each channel that are difficult to access experimentally. The overall rate coefficients exhibit a strong non-Arrhenius behaviour, which can be represented as: This is the first reported rate data for the glycerol carbonate and OH radicals reaction.}, language = {en} } @misc{EckartShresthaGirietal., author = {Eckart, Sven and Shrestha, Krishna P and Giri, Binod R and Fang, Qilong and Li, Wei and Mauss, Fabian and Krause, Hartmut and Li, Yuyang}, title = {Insight into premixed diethoxymethane flames: Laminar burning velocities, temperatures, and emissions behaviour}, series = {Proceedings of the Combustion Institute}, volume = {40}, journal = {Proceedings of the Combustion Institute}, publisher = {Elsevier}, doi = {10.1016/j.proci.2024.105579}, pages = {1 -- 7}, abstract = {Diethoxymethane ((CH3CH2O)2CH2, DEM) is a promising carbon-neutral fuel. DEM is a diether or acetal with a molecular structure similar to oxymethylene ethers (CH3O-(CH2O)n-CH3, OMEn). Thus, DEM can be expected to have a similar combustion behavior to OMEs, reducing harmful emissions such as NOx and particulate matter (PM) in internal combustion engines. From both experimental and kinetic modeling, fundamental studies on DEM are scarce in the literature. More studies are required to gain a detailed insight into the oxidation kinetics of DEM. Laminar burning velocity (LBV) is a critical property that allows a detailed assessment of the potential application of DEM in combustion devices. Unfortunately, the literature on the LBV of DEM is limited. Therefore, in this study we have investigated the LBV of DEM using two reactors for the first time, namely a heat flux burner and a combustion chamber. The experimental data is reported for equivalence ratio between 0.7 and 1.7, initial temperatures of 368-423 K, and initial pressure of 1-5 bar. In addition, we developed a detailed kinetic model extending our recent work of Shrestha et al. (Combust. Flame. 246 (2022) 112,426) to characterize the combustion behavior of DEM utilizing the new experimental data from this work and the literature data. Our model performs remarkably well in capturing the newly measured LBV experimental data over various experimental conditions. We found that DEM and dimethoxy methane (DMM) have similar values of LBVs (within ±1.5 cm/s) for a given condition, which indicates that intermediate chemistry governs the flame chemistry. Despite DEM being a larger molecule that is expected to have slightly lower LBVs than DMM, its effect on the measured values of LBVs is negligible. Finally, we experimentally measured NOx formation in DEM flame for the first time. The stochiometric flame has the highest NOx formation. The proposed model predicted the equivalence ratio dependence of NOx nicely. However, it overestimates the NOx formation for stoichiometric DEM/air mixtures by ∼30 \%. The model suggests that the thermal NO formation route is favored at lean and stochiometric conditions. In contrast, the prompt NO formation route is enhanced for rich mixtures.}, language = {en} } @misc{EckartShresthaGirietal., author = {Eckart, Sven and Shrestha, Krishna P and Giri, Binod R and Fang, Qilong and Chen, Chen and Li, Wei and Krause, Hartmut and Mauss, Fabian and Liu, Dong and Li, Yuyang}, title = {Chemical insights into ethyl acetate flames from experiment and kinetic modeling: Laminar burning velocity, speciation and NOx emission}, series = {Proceedings of the Combustion Institute}, volume = {40 (2024)}, journal = {Proceedings of the Combustion Institute}, publisher = {Elsevier}, doi = {10.1016/j.proci.2024.105487}, pages = {1 -- 7}, abstract = {Oxygenated fuels, such as alcohols, ethers, and esters, are promising alternatives to conventional fuels. These fuels can help reduce detrimental emissions like carbon monoxide and unburned hydrocarbons and enhance octane ratings. Among these oxygenates, ethyl acetate (EA), a small alkyl ester sourced from biomass, emerges as a clean, promising energy carrier. It serves as a surrogate fuel to facilitate investigations into the combustion behaviours of biodiesel. Despite its importance, the literature knowledge of EA combustion characteristics is limited. Therefore, this study aims to broaden the knowledge of the combustion behaviour of this type of oxygenated fuel compound. In this study, we measured the laminar burning velocities of EA by employing a heat flux burner and a closed combustion vessel over the equivalence ratios of 0.7 - 1.7, pressures of 1 - 10 bar and temperatures ranging from 353 - 423 K. Further, we also measured the NOx emissions in exhaust gas of the premixed flames fueled by EA/air for the first time over the equivalence ratio of 0.8 - 1.2. Additionally, we employed a non-premixed counterflow flame setup for extensive characterisation of species and their concentration under diverse conditions encompassing various strain rates and oxygen concentrations. Finally, we utilized these newly measured data to construct and validate a detailed kinetic model developed as part of this work. The newly developed model will help characterize the combustion properties of EA.}, language = {en} } @misc{ThomasShresthaMaussetal., author = {Thomas, Daniel E and Shrestha, Krishna P and Mauss, Fabian and Northrop, William F}, title = {Extinction and NO formation of ammonia-hydrogen and air non-premixed counterflow flames}, series = {Proceedings of the Combustion Institute}, volume = {39}, journal = {Proceedings of the Combustion Institute}, number = {2}, publisher = {Elsevier}, doi = {10.1016/j.proci.2022.08.067}, pages = {1803 -- 1812}, abstract = {Green ammonia, produced using renewable energy, is a promising carbon-free energy vector and fuel. This work studies combustion of ammonia-hydrogen fuel mixtures with air in counterflow diffusion flame experiments and provides an improved kinetic mechanism for modeling ammonia combustion. The extinction strain rate is measured for a range of 0 to 15\% hydrogen in the fuel blend. The flame structure is also investigated with quantitative laser-induced fluorescence (LIF) measurements of nitric oxide (NO) for the same hydrogen concentrations and strain rate range from 26 to 134 s. For these conditions, NO concentration increases with both strain rate and fuel hydrogen content. The previously published kinetic model developed by the authors is used to perform one-dimensional flame simulations of the experimental setup and conditions, and results are compared to three other recently published ammonia mechanisms. None of the selected models satisfactorily predict both the measured extinction strain rate and flame NO concentration. The models mainly fail to predict extinction strain rate at higher Hfraction and NO formation at the highest experimental strain rates and H fraction. The reaction rate parameters for some of the key reactions in the published model developed by authors were updated to improve agreement with experimental results. The updated model results are closely aligned with extinction strain rate measurements, and have improved prediction of flame NO concentration. The model reveals that the reactions from the NH and NH sub-mechanism are sensitive in predicting the extinction strain rate as well as NO. In particular, the reaction NH+NO=NO+H had significant impact on NO predictions.}, language = {en} } @misc{PasternakSiddareddydeSyniawaetal., author = {Pasternak, Michał and Siddareddy, Reddy Babu and de Syniawa, Larisa Le{\´o}n and Guenther, Vivien and Picerno, Mario and Andert, Jakob and Franken, Tim and Mauss, Fabian and Adamczyk, Wojciech}, title = {Plant modelling of engine and aftertreatment systems for X-in-the-loop simulations with detailed chemistry}, series = {CONAT 2024 International Congress of Automotive and Transport Engineering.}, journal = {CONAT 2024 International Congress of Automotive and Transport Engineering.}, publisher = {Springer Nature Switzerland}, address = {Cham}, isbn = {978-3-031-77626-7}, doi = {10.1007/978-3-031-77627-4_14}, pages = {151 -- 163}, abstract = {Use of numerical simulations at early stage of engine and aftertreatment systems development helps in evaluating their different concepts and reducing the need for costly building of prototypes. In this work, we explore the feasibility of fully physical and chemical-based tool-chain for co-simulating engine in-cylinder and aftertreatment processes. Detailed gas-phase reaction kinetics and surface chemistry mechanisms are applied for the modeling of combustion, pollutants formation and aftertreatment, respectively. Engine in-cylinder performance parameters are simulated using a stochastic reactor model and multi-component fuel surrogate. The engine model is coupled with an aftertreatment model capable of simulating diesel oxidation catalyst (DOC), selective catalytic reduction catalyst, lean NOx trap, ammonia slip catalyst, and three-way catalyst. Both the engine and aftertreatment models are embedded within the Simulink framework. They work in co-simulation and are coupled using Functional Mock-up Interface (FMI) technology. The coupled framework acts as a virtual test bench that is developed given its application for X-in-the-Loop (XiL) simulations. The framework can be applied to engine steady state or transient operating conditions. Here, exemplary calculations are performed using a Model-in-the-Loop (MiL) approach. Simulations are conducted under transient conditions of Worldwide Harmonized Light Vehicle Test Cycle for a compression ignition engine coupled with a DOC. The presented framework is considered a first step towards complex engine plant modeling using detailed chemistry for the virtualization of the development of engine, fuels and aftertreatment systems.}, language = {en} } @misc{MaussRakhi, author = {Mauss, Fabian and Rakhi, Rakhi}, title = {Numerical study of catalytic methanation reactions using a kinetic model}, series = {SAE Technical Paper}, journal = {SAE Technical Paper}, number = {2024-24-0022}, issn = {0148-7191}, doi = {10.4271/2024-24-0022}, pages = {5}, abstract = {Even if huge efforts are made to push alternative mobility concepts, such as, electric cars (BEV) and fuel cell powered cars, the importance and use of liquid fuels is anticipated to stay high during the 2030s. The biomethane and synthetic natural gas (SNG) might play a major role in this context as they are raw material for chemical industry, easy to be stored via existing infrastructure, easy to distribute via existing infrastructure, and versatile energy carrier for power generation and mobile applications. Hence, biomethane and synthetic natural gas might play a major role as they are suitable for power generation as well as for mobile applications and can replace natural gas without any infrastructure changes. In this paper, we aim to understand the direct production of synthetic natural gas from CO2 and H2 in a Sabatier process based on a thermodynamic analysis as well as a multi-step kinetic approach. For this purpose, we thoroughly discuss CO2 methanation to control emission in order to maximize the methane formation and minimize the CO formation and to understand the complex methanation process. We have considered an equilibrium and kinetic modelling study on the NiO-SiO2 catalyst for methanation focusing on CO2 derived SNG. In this work, a comprehensive thermodynamic analysis of CO2 hydrogenation is preformed to define the optimum process parameters followed by the kinetic simulations. Further, the simulations can be performed at various conditions, for example, catalyst mass, mass flow, pressure, temperature etc. to optimize the methanation process.}, language = {en} } @misc{MaussRakhi, author = {Mauss, Fabian and Rakhi, Rakhi}, title = {Numerical investigation of equilibrium and kinetic aspects for hydrogenation of CO2}, series = {Catalysts}, volume = {14}, journal = {Catalysts}, publisher = {MDPI}, doi = {10.3390/catal14090562}, pages = {1 -- 20}, abstract = {Even if huge efforts are made to push alternative mobility concepts, such as electric cars and fuel-cell-powered cars, the significance and use of liquid fuels is anticipated to stay high during the 2030s. Biomethane and synthetic natural gas (SNG) might play a major role in this context, as they are raw material for chemical industry that is easy to be stored and distribute via existing infrastructure, and are a versatile energy carrier for power generation and mobile applications. Since biomethane and synthetic natural gas are suitable for power generation and for mobile applications, they can therefore replace natural gas without any infrastructure changes, thus playing a major role.In this paper, we aim to comprehend the direct production of synthetic natural gas from CO2 and H2 in a Sabatier process based on a thermodynamic analysis as well as a multi-step kinetic approach. For this purpose, we thoroughly discuss CO2 methanation to control emissions in order to maximize the methane formation along with minimizing the CO formation and to understand the complex methanation process. We consider an equilibrium and kinetic modeling study on the NiO-SiO2 catalyst for methanation focusing on CO2-derived SNG. The thermodynamic analysis of CO2 hydrogenation is preformed to define the optimal process parameters followed by the kinetic simulations for catalyst development. The investigation presented in this paper can also be used for developing machine learning algorithms for methanation processes.}, language = {en} } @misc{SabiaMannaMaussetal., author = {Sabia, Pino and Manna, M.V. and Mauss, Fabian and Ragucci, R.}, title = {MILD Combustion stabilization issues through the analysis of hysteresis behaviors : the case of new energy carriers}, series = {Applications in Energy and Combustion Science}, volume = {19}, journal = {Applications in Energy and Combustion Science}, number = {September 2024}, doi = {10.1016/j.jaecs.2024.100276}, pages = {13}, abstract = {MILD combustion processes are renewed to reveal a strong resilience to extinction phenomena and/or instabilities, whereas the oxidation process is stabilized trough ignition phenomena. Under MILD conditions, igni-diffusive and/or perfectly mixed kernels, forming during the mixing process between hot products and fresh reactants, are so much diluted and pre-heated to escape classical feed-back flammable flames stabilization mechanisms, while ignition and extinction events merge in a unique condition through "anhysteretic" behaviors. So far, considering methane as reference fuel, it has been largely demonstrated the mentioned "anhysteretic" condition is very conservative and defines a sub-domain of MILD combustion processes, following Cavaliere and de Joannon's definition. Furthermore, the coincidence of ignition and extinction phenomena can occur also preserving hysteresis phenomena. In turns, this condition strongly enlarges the stabilization domain of MILD combustion processes, starting from the upper branch of the hysteresis behaviors to the real extinction, with characteristic unstable loci to consider as further/last opportunity to promote stable operative conditions through the formation of local thermo-kinetic conditions in the combustion chamber during hot products/fresh reactants mixing process (injection configuration/burner design), or by forced ignition events. The hysteresis behaviors of renewable/alternative fuels, relevant within the decarbonization policies of several energy sectors, are thoroughly discussed under MILD conditions through numerical studies in model reactors in order to shed light on common and/or different features, and outline practical rules towards the definition of stable MILD combustion domains. Results show that, as MILD combustion is a chemical kinetics-driven processes, stability issues have to be discussed in relation to fuel nature, albeit with common behavior can be derived. The coincidence between extinction/ignition phenomena is reached for extremely diluted conditions, already ascribable to MILD combustion conditions, thus defining a small sub-domain of the process. This condition can be reached through "hysteretic" or "anhysteretic" behaviors.}, language = {en} } @misc{VadivalaFrankenThapaetal., author = {Vadivala, Monang and Franken, Tim and Thapa, Ashish and Mauss, Fabian}, title = {Evaluation of metamodels for prediction of species concentration and reactor outlet temperature of Sabatier reactor}, abstract = {The production of green gases using Power-to-gas in industry and the energy sector is essential for reducing the carbon footprint. In this process, green hydrogen and carbon dioxide are converted into synthetic methane using nickel (Ni) catalysts. A one-dimensional (1D) model of a Sabatier reactor enables the simulation of transport processes in the porous medium and reaction kinetics on the Ni/Al2O3 catalyst.}, language = {en} } @misc{RakhiShresthaGuentheretal., author = {Rakhi, Rakhi and Shrestha, Krishna Prasad and G{\"u}nther, Vivien and Mauß, Fabian}, title = {Kinetically consistent detailed surface reaction mechanism for steam reforming of methane over nickel catalyst}, series = {Reaction Kinetics, Mechanisms and Catalysis}, volume = {135}, journal = {Reaction Kinetics, Mechanisms and Catalysis}, number = {6}, issn = {1878-5204}, doi = {10.1007/s11144-022-02314-7}, pages = {3059 -- 3083}, language = {en} } @misc{RakhiMauss, author = {Rakhi, Rakhi and Mauss, Fabian}, title = {Thermodynamic model : steam and oxidative reforming of methane over nickel catalyst}, series = {Reaction Kinetics, Mechanisms and Catalysis}, volume = {137}, journal = {Reaction Kinetics, Mechanisms and Catalysis}, number = {2}, publisher = {Springer}, doi = {10.1007/s11144-024-02571-8}, pages = {791 -- 812}, abstract = {In this paper, we have used a thermodynamic model for the first time to investigate the steam and oxidative reforming of methane over a nickel catalyst in a wide temperature range, i.e., 400-1200 K. The available literature focus on the kinetic models and hence, thermodynamic models require attention to understand the behaviour of the thermochemistry of the species involved in the mechanism. This study presents the comparison between the species concentration produced using the thermodynamic model against the available kinetic model to validate the results. The investigation is further extended, firstly, to perform the sensitivity analysis of the reactions involved in a thermodynamic model to figure out the most influential reactions at various temperatures and pressures. This allows us to compare the most influencing reactions in reforming process for kinetic and thermodynamic model to optimize the processes. Secondly, the reaction flow analysis is carried out for the thermodynamic model to comprehend the effect of the thermochemistry of the species and the major difference in the reaction pathways for both the models are noted.}, language = {en} } @misc{RakhiMauss, author = {Rakhi, and Mauss, Fabian}, title = {Optimising production of synthetic natural gas (SNG) from methane synthesis}, series = {Proceedings in applied mathematics and mechanics : PAMM}, volume = {25}, journal = {Proceedings in applied mathematics and mechanics : PAMM}, number = {1}, publisher = {Wiley-VCH GmbH}, address = {Weinheim}, issn = {1617-7061}, doi = {10.1002/pamm.202400044}, pages = {1 -- 5}, language = {en} } @misc{ShresthaMaiGirietal., author = {Shrestha, Krishna Prasad and Mai, Tam V.-T. and Giri, Sushant and Reddy, V. Mahendra and Szőri, Mil{\´a}n and Verma, Rakhi and Mauss, Fabian and Giri, Binod Raj and Huynh, Lam Kim}, title = {Reaction kinetics of NH₂ with H₂CO and CH₃CHO : modeling implications for NH₃-dual fuel blends}, series = {International journal of chemical kinetics}, volume = {57}, journal = {International journal of chemical kinetics}, number = {7}, publisher = {Wiley}, address = {New York}, issn = {0538-8066}, doi = {10.1002/kin.21781}, pages = {403 -- 416}, abstract = {Carbon-free fuels like ammonia (NH₃) and hydrogen (H₂) offer significant potential in combating global warming by reducing greenhouse gas emissions and moving toward zero carbon emissions. Over the past few years, our research has focused on understanding the combustion behavior of carbon-neutral and carbon-free fuels. In particular, we have explored the combustion characteristics of NH₃ when blended with various hydrocarbons and oxygenates. Our investigation revealed that carbon-nitrogen cross-chemistry plays a crucial role in shaping the combustion properties of NH3-hydrocarbon/oxygenate blends. Specifically, the chemistry of amino (NH₂) radicals is vital in influencing the low-temperature reactivity of these blends. Understanding the interactions between carbon and nitrogen is essential for optimizing combustion processes and improving the emissions profile of NH₃-based fuels. Recognizing the significance of this cross-chemistry, we investigated the reaction kinetics of NH₂ radicals with formaldehyde (H₂CO) and acetaldehyde (CH₃CHO) using high-level ab initio and transition state theory calculations. We computed the potential energy profiles of these reactions at the CCSD(T)/CBS//M06-2X/aug-cc-pVTZ level of theory to analyze the reactivity of NH2 radicals at various C─H bond sites. The newly derived rate constants have proven to be highly sensitive for modeling the low-temperature oxidation of NH₃-dual fuel blends, significantly enhancing the predictive accuracy of our previously published kinetic models. This work offers valuable insights into the role of NH₂ radicals, thereby advancing the development of NH₃-dual fuel systems.}, language = {en} } @misc{GiriMaiShresthaetal., author = {Giri, Binod Raj and Mai, Tam V.-T. and Shrestha, Krishna Prasad and Giri, Sushant and Naik, R. Thirumaleswara and Verma, Rakhi and Mauss, Fabian and Huynh, Lam K.}, title = {Theoretical kinetic study of NH₂ reactions with dimethyl ether and diethyl ether : implications for kinetic modeling}, series = {International journal of chemical kinetics}, volume = {57}, journal = {International journal of chemical kinetics}, number = {6}, publisher = {Wiley}, address = {Hoboken, NJ}, issn = {0538-8066}, doi = {10.1002/kin.21779}, pages = {353 -- 363}, abstract = {Ammonia (NH₃) and hydrogen (H₂) have emerged as promising carbon-free fuels to help mitigate global warming by reducing greenhouse gas emissions. Our ongoing research currently focuses on understanding the combustion characteristics of NH₃ blends with oxygenates and hydrocarbons, uncovering the critical role of carbon-nitrogen cross-reactions in accurately modeling their combustion behavior. Amino (NH₂) radicals, which are abundant in ammonia and nitrogen-rich environments, strongly influence the low-temperature reactivity of NH₃-hydrocarbon/oxygenate mixtures, affecting overall reactivity and emission characteristics. Recognizing the importance of NH₂ radicals, we investigated the reaction kinetics of NH₂ with dimethyl ether (DME, CH₃OCH₃) and diethyl ether (DEE, CH₃CH₂OCH₂CH₃) using appropriate high-level ab initio and statistical rate theory methods. We computed the potential energy profiles at the CCSD(T)/cc-pV(T, Q)Z//M06-2X/aug-cc-pVTZ level of theory, analyzing the reactivity of NH₂ radicals at various C─H sites of these diethers. Incorporating these newly derived rate parameters, our updated kinetic model successfully captures previous experimental data, addressing the modeling challenges encountered in our earlier studies. Our findings, including insights into the impact of NH₂ radicals, contribute to an understanding of ammonia combustion and its potential in achieving carbon-neutral energy systems.}, language = {en} } @misc{WernerKimMauss, author = {Werner, Adina and Kim, Jongmin and Mauss, Fabian}, title = {Pressure and temperature dependent UNIQUAC model for methanol - water mixtures}, series = {Fluid phase equilibria : an international journal}, volume = {599}, journal = {Fluid phase equilibria : an international journal}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {0378-3812}, doi = {10.1016/j.fluid.2025.114533}, pages = {1 -- 13}, abstract = {A pressure dependency is included in a quadratic temperature dependent binary interaction parameter of the UNIQUAC model. The obtained activity coefficients for methanol-water mixtures are compared with only temperature dependent UNIQUAC and UNIFAC, and with calculated activity coefficients based on experimental data between 298.15 - 373.15 K and 0.1519 - 1.01325 bar produced with vapor-liquid equilibrium calculations and Wilson method. This model exhibits an overall good agreement. The predicted activity coefficients are more adaptable than those from models without pressure dependence, indicating potential for further improvement.}, language = {en} } @misc{FrankenMaussSharmaetal., author = {Franken, Tim and Mauss, Fabian and Sharma, Saurabh and Brueger, Arnim and Lepka, Marco}, title = {Optimization of oxyfuel biogas combustion in combined heat and power plants : a multi-criteria study}, series = {32. Deutscher Flammentag - Paderborn, Germany: 15th - 17th September 2025}, journal = {32. Deutscher Flammentag - Paderborn, Germany: 15th - 17th September 2025}, abstract = {This paper investigates the influence of oxygen addition on the combustion of biogas and biomethane in a combined heat and power plant using numerical methods. A multi-objective optimization platform was established, employing a stochastic engine model with detailed chemistry to predict oxyfuel combustion and emission formation. Additionally, a hybrid optimization algorithm, combining NSGA-II and metamodels, was utilized to conduct the optimization. The optimization results indicate that the lowest indicated specific fuel consumption was achieved with biomethane, while the lowest NOx emissions were attained with biogas. An increase in oxygen addition proved beneficial for reducing specific fuel consumption. However, higher oxygen addition rates resulted in increased NOx emissions.}, language = {en} } @misc{AsgarzadeFrankenMauss, author = {Asgarzade, Rufat and Franken, Tim and Mauss, Fabian}, title = {Experimental investigation of CH4/O2/CO2 mixtures in a single-cylinder spark ignition engine}, pages = {1}, abstract = {The Power-to-X-to-Power (P2X2P) technology involves producing synthetic methane from renewable hydrogen and captured CO2, which is then used for cogeneration of electricity and heat through oxyfuel combustion. With the P2X2P energy system demonstrator, NOx-free and carbon neutral heat and electricity generation as well as storage of excess renewable energy are realized. This work presents the experimental investigation of combustion characteristics for CH4/O2/CO2 mixtures in a single cylinder spark ignition engine that is a part of the P2X2P system.}, language = {en} } @misc{AsgarzadeFrankenMauss, author = {Asgarzade, Rufat and Franken, Tim and Mauss, Fabian}, title = {Development of an oxyfuel engine test bench for power-to-X-to-power application}, series = {12th European Combustion Meeting}, journal = {12th European Combustion Meeting}, pages = {1}, abstract = {This work presents the development of an oxyfuel engine test bench which is integrated into a Power-to-X-to-Power energy storage system demonstrator. These storage systems are considered carbon-free because they recirculate carbon without emitting it into the atmosphere.}, language = {en} } @misc{AsgarzadeFrankenMauss, author = {Asgarzade, Rufat and Franken, Tim and Mauss, Fabian}, title = {Oxyfuel combustion process development for an SI engine in a power-to-X-to-power energy system}, pages = {1}, abstract = {This work presents the development of an oxyfuel engine test bench which is to be integrated to a Power-to-X-to-Power energy storage system demonstrator. Such storage systems are considered carbon-neutral because they recirculate carbon without emitting it into the atmosphere.}, language = {en} } @misc{WernerKimMauss, author = {Werner, Adina and Kim, Jongmin and Mauss, Fabian}, title = {Excess volumes calculated from UNIQUAC model using the example of methanol - water mixtures}, series = {Fluid phase equilibria}, volume = {603}, journal = {Fluid phase equilibria}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {0378-3812}, doi = {10.1016/j.fluid.2025.114650}, pages = {1 -- 13}, abstract = {Excess volumes can be calculated generally via equations of state. In this work, the excess volumes are obtained using the UNIQUAC model with two approaches of a temperature- and pressure-dependent binary interaction parameter. The pressure dependency is required as the excess volume is derived from the pressure dependency of the excess free enthalpy. Both UNIQUAC approaches are successfully able to predict the vapor-liquid equilibrium as well as the excess volume of methanol-water mixtures over a temperature range between 288.15-473 K and a pressure range between 0.1519-134 bar using a single optimized parameter set.}, language = {en} } @misc{FrankenVermaSharmaetal., author = {Franken, Tim and Verma, Rakhi and Sharma, Saurabh and Gloesslein, Tobias and Brueger, Arnim and Mauss, Fabian}, title = {Modeling of synthetic methane production using Gaussian processes regression}, series = {CYPHER Workshop on "Digital Twins for the Decarbonization of hard-to-abate industries"}, journal = {CYPHER Workshop on "Digital Twins for the Decarbonization of hard-to-abate industries"}, abstract = {The production of green gases using Power-to-gas in industry and the energy sector is essential for reducing the carbon footprint. In this process, green hydrogen and carbon dioxide are converted into synthetic methane using nickel catalysts. The carbon dioxide can be obtained from the environment or from point sources such as waste-to-energy plants, combined heat and power plants or industrial furnaces. A one-dimensional model of methane synthesis in the Sabatier reactor enables the simulation of transport processes in the porous medium and the reaction kinetics on the active surface of the nickel catalyst. Despite the low dimensionality, the reactor model is still computationally intensive, as it must solve the reaction mechanism of heterogeneous surface reactions and the mass and heat transport. The introduction of Gaussian processes regression can help to significantly reduce the computational effort for the prediction of species and temperature in the Sabatier reactor under different thermodynamic conditions. This allows for faster turnaround times, enables the application of advanced methods like optimization and more. The accuracy of a Gaussian processes regression is investigated in this work.}, language = {en} } @misc{ShresthaGiriPeleetal., author = {Shrestha, Krishna Prasad and Giri, Binod Raj and Pel{\´e}, Ronan and Aljohani, Khalid and Brequigny, Pierre and Mauss, Fabian and Halter, Fabien and Huynh, Lam K. and Mouna{\"i}m-Rousselle, Christine}, title = {A comprehensive chemical kinetic modeling and experimental study of NH₃-methanol/ethanol combustion towards net-zero CO₂ emissions}, series = {Combustion and flame}, volume = {274}, journal = {Combustion and flame}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {0010-2180}, doi = {10.1016/j.combustflame.2024.113954}, pages = {1 -- 21}, abstract = {Ammonia is gaining attention as a green fuel with the potential to reduce carbon emissions. Its versatility allows it to be used directly in combustion engines, fuel cells, and as a hydrogen carrier, making it a key candidate for sustainable energy applications. This study provides a comprehensive analysis of the oxidation kinetics of ammonia (NH3) blends with methanol (CH3OH) and ethanol (C2H5OH) under diverse conditions. We measured laminar flame speeds of different NH3-alcohol blends — varying CH3OH/C2H5OH ratios (0-100 \%) — using a constant volume combustion chamber across temperatures from 503 to 645 K and pressures of 2-11.3 bar. We also obtained the ignition delay times for NH3/C2H5OH blends with 10 \% and 30 \% (by mole) C2H5OH using a shock tube at pressures of 1, 10, and 20 bar and temperatures of 1100-1500 K. Our results show that incorporating CH3OH and C2H5OH into NH3 increases the laminar flame speed, with C2H5OH being a more effective promoter than CH3OH due to its higher contribution to the formation of reactive radicals (OH, H, and O). Our model suggests that at high temperatures, both CH3OH and C2H5OH contribute to increased NO formation, with C2H5OH being more effective in reducing N2O emissions than CH3OH. In shock tube experiments, adding C2H5OH significantly shortens ignition delay times of NH3. At low temperatures (in the rapid compression machine case), the sensitivity to ignition delay times decreases when the CH3OH/C2H5OH content exceeds 5 \% in NH3-alcohol blends. C2H5OH is a more effective combustion promoter, enhancing NH3 reactivity and reducing NOx emission more efficiently than CH3OH. We developed a detailed kinetic model, building on our previous work, and validated it against new experimental and literature data. Our model accurately predicts the combustion behavior of neat NH3 and NH3 fuel blends and serves as a base for future research on NH3 blended with higher hydrocarbons and/or oxygenated blends.}, language = {en} } @misc{PasternakPrzybyłaSiddareddyetal., author = {Pasternak, Michał and Przybyła, Grzegorz and Siddareddy, Reddy and Lewandowski, Michał and Bj{\o}rgen, Karl and Mauss, Fabian and Nadimi, Ebrahim and Peczkis, Grzegorz and Zhou, Min-min and Adamczyk, Wojciech}, title = {Development of ammonia-biodiesel fueled agricultural tractor : aspects of retrofitting a compression ignition engine to direct ammonia injection}, series = {Energy}, volume = {327}, journal = {Energy}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {0360-5442}, doi = {10.1016/j.energy.2025.136255}, pages = {1 -- 14}, abstract = {The automotive industry has shown growing interest in ammonia as a carbon-free fuel, which holds potential for mitigating the greenhouse effect. Nonetheless, adapting current combustion engines to use ammonia necessitates prior modifications. This paper introduces a retrofitting technique for converting an existing compression ignition engine into one powered by a direct injection of ammonia and biodiesel. The development results from collaboration between Polish and Norwegian research teams as part of the ACTIVATE project (Ammonia as carbon-free fuel for internal combustion engine-driven agricultural vehicles). The new technology is grounded on experimental and numerical research involving a single-cylinder engine installed in a small agricultural tractor. Biodiesel was directly injected to initiate ammonia combustion. Experimental activities were performed on engine test benches and a chassis dynamometer, complemented by 0D and 3D simulations using the stochastic reactor model and CFD code Converge, respectively. A comprehensive exploration of engine operating conditions and fuel injection strategies was undertaken experimentally and numerically to assess the potential benefits and drawbacks of various designs. A segment of the research focused on analyzing nitrous oxide formation, given its significant impact on global warming. The investigations resulted in a method for combusting ammonia with biodiesel as an ignition enhancer. It was determined that maintaining a stable engine operation in a tractor under real driving scenarios requires 47\% of the energy sourced from ammonia. Optimal engine performance occurs when ammonia and biodiesel are injected near the end of the compression stroke, closely followed by the ignition promoter. A prolonged interval between these injections impairs combustion efficiency and raises ammonia emissions. The integrated numerical and experimental research resulted in a demonstration tractor fueled by directly injected biodiesel and ammonia.}, language = {en} } @misc{HemaiziaVermaGuanetal., author = {Hemaizia, Abdelkader and Verma, Rakhi and Guan, Wei and Mauss, Fabian and Th{\´e}venin, Dominique}, title = {The influence of hydrocarbon additives on laminar burning velocity and NOx emissions in hydrogen-air combustion}, series = {Proceedings in applied mathematics and mechanics : PAMM}, volume = {25}, journal = {Proceedings in applied mathematics and mechanics : PAMM}, number = {4}, editor = {Mauss, Fabian}, publisher = {Wiley}, address = {Weinheim}, issn = {1617-7061}, doi = {10.1002/pamm.70028}, pages = {1 -- 13}, abstract = {Hydrogen is a promising carbon-free fuel but faces challenges due to combustion instability and nitrogen oxide () emissions during combustion. This study investigates the potential of blending hydrocarbons (methane, propane) or ammonia with hydrogen-air flames in order to minimize these challenges. Simulations were performed using a one-dimensional, freely-propagating, adiabatic premixed flame (FPPF) model in Cantera, incorporating detailed kinetic and thermodynamic modeling. Updated, detailed, and reduced reaction mechanisms were utilized to accurately represent the chemical kinetics of the selected fuel blends. We analyzed laminar flame velocity (LFV), flame structure, and emissions of and CO across a range of inlet pressures, temperatures, equivalence ratios, and blend ratios of /, /, and /. The results were validated against experimental data. Propane addition (10\% -60\% vol.) was found to be the most effective solution to reduce emissions by promoting reburning pathways that convert NO to , while moderately reducing LFV. Methane exhibits a comparable effect in suppressing thermal while slightly reducing LFV. Ammonia drastically lowers via fuel-bound nitrogen pathways but sharply increases CO emissions and destabilizes flames at high concentrations. By identifying key reaction pathways governing formation (thermal, prompt, , NNH, and reburning), propane is finally selected as the optimal additive for achieving low- hydrogen combustion, despite its trade-off with LFV, providing critical insights for designing cleaner and more stable combustion systems.}, language = {en} } @misc{VermaGuentherGirietal., author = {Verma, Rakhi and G{\"u}nther, Vivien and Giri, Binod Raj and Hemaizia, Abdelkader and Th{\´e}venin, Dominique and Mauss, Fabian}, title = {Kinetic modeling of CO₂ methanation for methane production : a comprehensive study}, series = {IFAC-PapersOnLine}, volume = {59}, journal = {IFAC-PapersOnLine}, number = {29}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {2405-8963}, doi = {10.1016/j.ifacol.2025.12.175}, pages = {18 -- 23}, abstract = {To understand the complex methanation reaction, experiments have been conducted at various operating conditions, for instance, temperature, inlet gas dilution, and inlet composition. In addition, a detailed surface reaction mechanism is developed to conduct the study numerically by validating the simulation results with the experimental data. The kinetic model developed in this study is able to capture the experimental trends successfully for all conditions considered for the analysis.}, language = {en} } @misc{VermaGuentherGirietal., author = {Verma, Rakhi and G{\"u}nther, Vivien and Giri, Binod Raj and Mauss, Fabian}, title = {Effect of pressure and nitrogen dilution on surface species and reaction kinetics in CO₂ methanation over Ni catalyst}, series = {IFAC-PapersOnLine}, volume = {59}, journal = {IFAC-PapersOnLine}, number = {29}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {2405-8963}, doi = {10.1016/j.ifacol.2025.12.172}, pages = {1 -- 5}, abstract = {The CO2 methanation process is studied under varying pressures to support the development of efficient and sustainable technologies aligned with emission reduction and hydrogen economy goals. Experiments at two pressures, followed by pressure-dependent simulations, show strong agreement. Additionally, surface species coverage is analyzed, offering insights into catalytic behavior. These findings aid in optimizing methanation by deepening understanding of reaction mechanisms and guiding the design of improved catalysts.}, language = {en} } @misc{VermaMauss, author = {Verma, Rakhi and Mauss, Fabian}, title = {Equilibrium analysis for methanation focusing on CO₂ derived substitute natural gas}, series = {Proceedings of the Second SIMS EUROSIM Conference on Modelling and Simulation, SIMS EUROSIM 2024}, volume = {211}, journal = {Proceedings of the Second SIMS EUROSIM Conference on Modelling and Simulation, SIMS EUROSIM 2024}, publisher = {Link{\"o}ping University Electronic Press}, address = {Link{\"o}ping}, isbn = {978-91-8075-984-7}, issn = {1650-3686}, doi = {10.3384/ecp212.022}, pages = {162 -- 167}, abstract = {In this study the methanation of synthesis gas (syngas) is investigated with a focus on achieving maximum methane and minimum CO by full methanation of CO2. For this study, we have considered a comprehensive thermodynamics analysis of CO2 hydrogenation. This will help us to understand the thermodynamic behaviour of the reactions involved in the methanation process. We have discussed the behavior of the species, CO2, H2, CH4, and H2O at the equilibrium with temperature, pressure, and fuel ratio variation in order to get the desired output. The preliminary study will focus on selecting the optimum conditions (temperature, pressure, and H2/CO2 ratio) for performing the experiments and for catalyst development.}, language = {en} } @misc{HemaiziaVermaMaussetal., author = {Hemaizia, Abdelkader and Verma, Rakhi and Mauss, Fabian and Th{\´e}venin, Dominique}, title = {On the impact of swirl number on premixed C3H8/air combustion in a bluff-body burner}, series = {IFAC-PapersOnLine}, volume = {59}, journal = {IFAC-PapersOnLine}, number = {29}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {2405-8963}, doi = {10.1016/j.ifacol.2025.12.201}, pages = {174 -- 179}, abstract = {Utilizing ANSYS-Fluent 21.0, large eddy simulations (LES) of the reactive flow in the Volvo bluff-body burner under various swirl intensities were performed. The Eddy Dissipation Concept (EDC) model coupled with a reduced chemical mechanism was employed to simulate premixed combustion. Results show thatLES is able to capture the interaction between swirl strength and fame stabilization behind the bluff-body. High swirl numbers generate strong central recirculation zones (CRZ), which enhance fame anchoring and combustion efficiency through increased hot gas recirculation and improved turbulent mixing.}, language = {en} } @misc{SiddareddyPasternakdeSyniawaetal., author = {Siddareddy, Reddy Babu and Pasternak, Michał and de Syniawa, Larisa Le{\´o}n and Guenther, Vivien and Seidel, Lars and Mauss, Fabian and Przybyła, Grzegorz and Adamczyk, Wojciech}, title = {Simulations of the SCR catalyst in ammonia-biodiesel fuelled CI engine using virtual test bench with detailed chemistry}, series = {Renewable energy}, volume = {251}, journal = {Renewable energy}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {0960-1481}, doi = {10.1016/j.renene.2025.123169}, pages = {1 -- 12}, abstract = {The use of ammonia as an alternative fuel in the automotive industry is not yet fully established. Further research and development are required to account for both engine and aftertreatment systems, as well as their integration and control to ensure the most efficient use of ammonia. In this work, we present a fully physics and chemistry-based toolchain for co-simulating an ammonia-biodiesel fuelled compression ignition engine with a selective catalytic reduction catalyst. The investigations refer to experimental data from a single-cylinder research engine. This is a direct injection engine that was retrofitted to run on ammonia and biodiesel, the latter acting as a combustion promoter. Engine in-cylinder processes were simulated using a stochastic reactor model. Detailed gas phase chemistry is used to simulate the combustion process and pollutants formation. The catalyst model employs detailed surface chemistry that is trained using available data from literature. Eventually, the co-simulation toolchain was applied to investigate numerically the impact of the properties of the catalyst on ammonia reduction under engine-relevant operating conditions}, language = {en} } @misc{WelpRudolphGirietal., author = {Welp, Alexandra and Rudolph, Charlotte and Giri, Binod Raj and Shrestha, Krishna Prasad and Verma, Rakhi and Mauss, Fabian and Atakan, Burak}, title = {Oxidation kinetics of ammonia methanol blends : an experimental and kinetic modeling study}, series = {Combustion and flame}, volume = {278}, journal = {Combustion and flame}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {0010-2180}, doi = {10.1016/j.combustflame.2025.114210}, pages = {1 -- 11}, abstract = {Ammonia is emerging as a key hydrogen energy carrier for decarbonization. However, its low reactivity necessitates blending with hydrocarbons and/or oxygenates, such as alcohols, to improve combustion properties. Understanding the oxidation kinetics of such blends is essential for evaluating ammonia's potential as a sustainable fuel. The experimental data on ammonia blended with simple alcohols like methanol remains scarce. This study investigates the oxidation kinetics of ammonia/methanol blends for the first time using a plug-flow reactor coupled with a time-of-flight mass spectrometer setup. This advanced setup enabled simultaneous quantification of temperature-dependent reactant conversion and product distribution over a temperature range of 373-973 K, a pressure of 3 bar, and equivalence ratios of 1 and 2. Adding 10 \% methanol significantly enhances radical formation, reducing oxidation onset temperature compared to neat ammonia. Interestingly, the conversion onset temperature was only slightly influenced by the mixture composition or the equivalence ratio. The temperature dependence of the product distribution as a function of the equivalence ratio was further analyzed. Experimental results were compared to simulation using selected kinetic models from the literature, revealing significant disparities in predicting capabilities. Among the kinetic models, Shrestha 2025, He 2023 and Wang 2024 performed well, capturing our experimental data for NH3/CH3OH blends. Reaction flux and sensitivity analyses highlighted some key reactions involving the reactive combustion species (OH, HO2 and NH2), such as CH3OH+HO2 ⇌ CH2OH+H2O2 and CH3OH+NH2, governing the oxidation kinetics of NH3/CH3OH blends. This combined experimental and kinetic modeling approach provides valuable insights into fundamental reaction mechanisms of NH3/CH3OH blends, aiding the development of cleaner and more efficient combustion systems.}, language = {en} } @misc{RotheBikasMauss, author = {Rothe, Paul and Bikas, Georgios and Mauss, Fabian}, title = {Investigation of the combustion process of a thermally conditioned active prechamber in monovalent operation with ammonia}, series = {SAE technical papers}, journal = {SAE technical papers}, publisher = {SAE International}, address = {Warrendale, PA}, issn = {0148-7191}, doi = {10.4271/2025-24-0028}, pages = {13}, abstract = {The debate over synthetic fuels is intense especially in sectors with a high energy demand like maritime [1, 2]. Hydrogen production from renewable sources is growing, but immediate measures for decarbonization are needed [3, 4]. In this context, the project MethMag was funded, and a gas engine for methane combustion with an innovative cooling concept and a purged prechamber (PC) spark plug was virtually developed [5, 6]. Validation with data from the test bench demonstrates that the simulations accurately represent the operating conditions [7, 8]. This combustion process is adapted for ammonia, which is being considered as a climate-friendly fuel of the future, particularly in maritime transportation [4, 9]. This fuel faces significant combustion challenges and is therefore mostly considered in complex, bivalent systems [10]. In particular, the prechamber is examined regarding the ignitability of ammonia. The overarching objective is to eliminate the necessity for a secondary fuel system, thereby reducing system complexity and associated costs. The transition to ammonia highlights the need for further adjustments. The geometry of the PC cap significantly affects turbulence and mixture formation in the prechamber [11]. While swirl caps generate high turbulence, the mixture formation is inadequate. Tumble caps, on the other hand, provide advantages in mixture formation by achieving an earlier increase in turbulence, even though the maximum turbulence is lower. For ammonia combustion, PC wall conditioning is not essential, given the inherently low combustion temperatures. However, conditioning can improve cold-start behavior by accelerating PC combustion and offering greater flexibility in ignition timing [12]. Direct injection into the prechamber enhances fuel mixing and reduces sensitivity to ignition timing adjustments. This leads to higher efficiency and better combustion characteristics, particularly at lean air-fuel ratios [13, 14]. Operating with a lean ammonia-air mixture is challenging but offers benefits for non-selective catalytic reduction (non-SCR) of nitrogen oxides. Simulations show that operation with λ = 1.2 and λ = 1.4 is feasible, although efficiency decreases at leaner mixtures [15].}, language = {en} } @misc{UdaybhanuGiriLeeetal., author = {Udaybhanu, Gadi and Giri, Binod R. and Lee, Bok Jik and Shrestha, Krishna P. and Roberts, William L and Mauss, Fabian and Reddy, V. Mahendra}, title = {Investigation of staging techniques for hydrocarbon-assisted ammonia flames in a novel dual-stage combustor}, series = {Combustion and flame}, volume = {284}, journal = {Combustion and flame}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {0010-2180}, doi = {10.1016/j.combustflame.2025.114607}, pages = {1 -- 12}, abstract = {Ammonia presents itself as a high-hydrogen dense and carbon-free alternative for industrial heating, power generation, and transportation. Nevertheless, the challenges of its low flame speed and elevated NOx (nitrogen oxides) emissions pose significant challenges in combustor applications. This study investigates a novel two-stage burner employing a radial injection staging technique and explores various NOx reduction strategies for hydrocarbon-assisted ammonia flames. These strategies include premixing, fuel staging, balanced fuel staging, air staging, and sequential premixing. The focus is on LPG (liquid petroleum gas)-stabilized ammonia flames. The experiments are conducted at a constant thermal input of 20 kW (10 kW LPG + 10 kW NH3), with global equivalence ratios ranging from 0.7 to 1.4. This approach aims to provide valuable insights into the effectiveness of different staging strategies for NOx reduction in ammonia combustion. Experimental analysis is undertaken to ascertain the flame stabilization, flame temperature and its reaction zone, intermediate species and major emissions like NOx and NH3 of the burner. Staging configuration strongly influenced flame stabilization, heat release distribution, and thermal field, with downstream-shifted combustion zones lowering peak temperatures and NOx formation. Among the tested strategies, fuel staging and sequential premixing consistently achieved the greatest NOx reduction across the entire operating range compared to the premixed baseline, without compromising flame stability. Chemical kinetics analysis further reveals the dominant NO formation pathways, highlighting the key roles of HNO and NHi radicals. Additionally, this analysis helps identify dominant reaction routes and the role of intermediate species in NO formation and reduction processes. The combined experimental and kinetic insights provide a mechanistic basis for optimizing staged combustion of ammonia-hydrocarbon blends for lower NOx emissions.}, language = {en} } @misc{AsgarzadeFrankenMauss, author = {Asgarzade, Rufat and Franken, Tim and Mauss, Fabian}, title = {Multi-objective optimization of oxyfuel gas engine using stochastic engine model and detailed chemistry}, series = {SAE technical papers}, journal = {SAE technical papers}, editor = {Hemaizia, Abdelkader}, publisher = {SAE International}, address = {Warrendale, PA, United States}, issn = {0148-7191}, doi = {10.4271/2025-01-0529}, pages = {13}, abstract = {The energy transition initiatives in Germany's renown coal mining region Lusatia have driven research into Power-to-X-to-Power technologies, where synthetic fuel is produced from renewably sourced hydrogen and captured CO2, and converted to electricity and heat through oxyfuel combustion. This work investigates the multi-objective optimization of oxyfuel gas engine using a stochastic engine model and detailed chemistry. Exhaust gas recirculation (EGR) rate, initial cylinder temperature and pressure, spark timing, piston bowl radius and depth are selected as design parameters to minimize the exhaust temperature at exhaust valve opening and indicated specific fuel consumption (ISFC) corresponding to oxyfuel operation with different dry and wet EGR rates. The optimization problem is solved for a dry EGR and four wet EGR cases with various CO2/H2O fractions, aiming to achieve comparable performance as in conventional natural gas / air operation, and energy-efficient carbon capture. The case with the lowest humidity (T10deg) had the lowest temperature of 1537 K, while the one with the highest vapor fraction (T70deg) attained the minimum 260 g/kWh ISFC. The superiority of the T10deg case is offset by much higher cooling demand (3.06 kW) for CO2 separation than that for T70deg case (0.81 kW). The constraint for combustion efficiency (>65\%) limited the solution space towards high ISFC values, while the constraint for low indicated mean effective pressure (IMEP) (>7 bar) and the constraint for high IMEP (<8 bar) limited the solution space in between the two distinct clusters of feasible designs, and towards high exhaust temperature, respectively. The optimized designs from all the cases could outperform the reference case in terms of IMEP, nevertheless they fell below 31\% indicated efficiency, which is associated with stoichiometric combustion.}, language = {en} } @misc{ElHarrabAskarFrankenetal., author = {El Harrab, Hayat and Askar, Enis and Franken, Tim and Mauss, Fabian}, title = {Experimental and reaction kinetic study of hydrogen ignition behavior at ignition limits}, series = {Proceedings of the Combustion Institute}, volume = {41}, journal = {Proceedings of the Combustion Institute}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {1540-7489}, doi = {10.1016/j.proci.2025.105980}, pages = {1 -- 7}, abstract = {The paper presents the results of an experimental and reaction kinetic investigation of hydrogen ignition at different pressures in a closed vessel, highlighting its non-linear behavior and the effects of radical wall termination. The reaction kinetic simulation predicts the three characteristic ignition limits of hydrogen caused by radical and thermal auto-ignition and is in close agreement with the experimental measurements. The first ignition limit is determined by the chain branching reaction . This limit shows strong sensitivity towards the wall termination of O, H and OH radicals. The second ignition limit is influenced by the wall termination of O, H, OH, HO2 and H2O2 radicals. The third ignition limit is dominated by the reaction paths and , which is why it shows strong sensitivity towards wall termination of HO₂ and H₂O₂ radicals. Increasing the radical wall termination rate by increasing the sticking coefficient of the radicals at the wall or the surface-to-volume-ratio leads to an increase of the auto-ignition temperature at the same pressure. The introduction of radical wall termination reactions improved the prediction of ignition limits and highlighted the profound effect of the autoclave wall and vessel size on the hydrogen ignition behavior.}, language = {en} }