TY - GEN A1 - Rakhi, Rakhi A1 - Giri, Binod Raj A1 - Günther, Vivien A1 - Mauss, Fabian T1 - Insight into the thermodynamic model for reforming of methane over nickel catalyst T2 - Proceedings of the 64th International Conference of Scandinavian Simulation Society, SIMS 2023 Västerås, Sweden, September 25-28, 2023 N2 - The reforming of light hydrocarbons to produce synthesis gas, H2 and CO, is an important intermediate for manufacturing valuable basic chemicals and synthesis fuels. In order to understand these reforming processes better, elementary step reaction mechanisms are developed. In the available literature, the surface reaction mechanisms are usually achieved with the help of reaction kinetic parameters without using the thermochemistry of the species referred to kinetic models due to the unavailability of the thermochemistry of the intermediate species involved in the multi-step reaction mechanism. In this work, investigations are made to obtain the thermochemistry of the intermediate species to establish thermodynamic equilibrium in order to develop a thermodynamic model for steam reforming of methane over nickel. The thermochemistry of the surface bound species is taken from different sources available in the literature and after that a detailed sensitivity analysis is performed to match the results with experiments. The simulation set up is adapted from the literature experiments given in [1]. The results produced with the one-dimensional tool using the thermodynamic model developed in the present investigation consisting of 21 reversible reactions are compared with the kinetic scheme with 42 irreversible reactions from reference simulation along with their experimental results. Both the models show some major differences in the reaction pathways which provides a useful insight into the key rate determining steps and needs further investigations. Y1 - 2023 UR - https://ecp.ep.liu.se/index.php/sims/article/view/766 U6 - https://doi.org/10.3384/ecp200025 SP - 192 EP - 197 ER - TY - GEN A1 - Richter, Jana A1 - Günther, Vivien A1 - Mauß, Fabian T1 - Reaction mechanism development and investigation on the convergence influence in a 1D catalyst model for a γ-alumina stabilized three-way catalyst T2 - The Proceedings of the International symposium on diagnostics and modeling of combustion in internal combustion engines N2 - 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. Y1 - 2022 UR - https://www.jstage.jst.go.jp/article/jmsesdm/2022.10/0/2022.10_A10-3/_article/-char/en U6 - https://doi.org/10.1299/jmsesdm.2022.10.A10-3 SN - 2424-2918 ER - TY - GEN A1 - Leon de Syniawa, Larisa A1 - Siddareddy, Reddy Babu A1 - Oder, Johannes A1 - Franken, Tim A1 - Günther, Vivien A1 - Rottengruber, Hermann A1 - Mauß, Fabian T1 - 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 T2 - SAE Technical Report N2 - 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. KW - Exhaust Emissions KW - Tail Pipe Emissions KW - Three Way Catalyst KW - Gas Engines KW - Cold Start KW - Simulation KW - Detailed Chemistry KW - Methane Oxidation Catalyst KW - Methane KW - Co-Simulation KW - Catalysts Y1 - 2023 U6 - https://doi.org/10.4271/2023-01-0364 SN - 2688-3627 SN - 0148-7191 ER - TY - GEN A1 - Rakhi, Rakhi A1 - Günther, Vivien A1 - Mauß, Fabian T1 - A detailed surface reaction mechanism to investigate oxidation of methane over nickel catalyst T2 - Proceedings in Applied Mathematics & Mechanics : PAMM N2 - 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. Y1 - 2023 U6 - https://doi.org/10.1002/pamm.202200055 SN - 1617-7061 N1 - Special Issue: 92nd Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM) VL - 22 IS - 1 ER - TY - GEN A1 - Rakhi, Rakhi A1 - Günther, Vivien A1 - Mauß, Fabian T1 - Insights into dry reforming of methane over nickel catalyst using a thermodynamic model T2 - Reaction Kinetics, Mechanisms and Catalysis N2 - 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. Y1 - 2023 U6 - https://doi.org/10.1007/s11144-023-02426-8 SN - 1878-5204 SN - 1878-5190 ER - TY - GEN A1 - Leon de Syniawa, Larisa A1 - Siddareddy, Reddy Babu A1 - Prehn, Sascha A1 - Günther, Vivien A1 - Franken, Tim A1 - Buchholz, Bert A1 - Mauß, Fabian T1 - Simulation of CNG Engine in Agriculture Vehicles. Part 2: Coupled Engine and Exhaust Gas Aftertreatment Simulations Using a Detailed TWC Model T2 - SAE Technical Paper N2 - 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 KW - CNG KW - Cold start KW - Afterteatment KW - Three-Way Catalyst KW - Surface chemistry KW - Simulation Y1 - 2023 U6 - https://doi.org/10.4271/2023-24-0112 SN - 0148-7191 SN - 2688-3627 ER - TY - GEN A1 - Richter, Jana A1 - Rachow, Fabian A1 - Israel, Johannes A1 - Roth, Norbert A1 - Charlafti, Evgenia A1 - Günther, Vivien A1 - Flege, Jan Ingo A1 - Mauß, Fabian T1 - Reaction Mechanism Development for Methane Steam Reforming on a Ni/Al2O3 Catalyst T2 - Catalysts N2 - In this work, a reliable kinetic reaction mechanism was revised to accurately reproduce the detailed reaction paths of steam reforming of methane over a Ni/Al2O3 catalyst. A steady-state fixed-bed reactor experiment and a 1D reactor catalyst model were utilized for this task. The distinctive feature of this experiment is the possibility to measure the axially resolved temperature profile of the catalyst bed, which makes the reaction kinetics inside the reactor visible. This allows for understanding the actual influence of the reaction kinetics on the system; while pure gas concentration measurements at the catalytic reactor outlet show near-equilibrium conditions, the inhere presented temperature profile shows that it is insufficient to base a reaction mechanism development on close equilibrium data. The new experimental data allow for achieving much higher quality in the modeling efforts. Additionally, by carefully controlling the available active surface via dilution in the experiment, it was possible to slow down the catalyst conversion rate, which helped during the adjustment of the reaction kinetics. To assess the accuracy of the revised mechanism, a monolith experiment from the literature was simulated. The results show that the fitted reaction mechanism was able to accurately predict the experimental outcomes for various inlet mass flows, temperatures, and steam-to-carbon ratios. KW - kinetic reaction mechanism development KW - 1D modeling KW - reaction rates KW - methane steam reforming KW - fixed-bed reactor experiments KW - nickel catalyst Y1 - 2023 U6 - https://doi.org/10.3390/catal13050884 SN - 2073-4344 VL - 13 IS - 5 ER - TY - GEN A1 - Rakhi, Rakhi A1 - Shrestha, Krishna Prasad A1 - Günther, Vivien A1 - Mauß, Fabian T1 - Kinetically consistent detailed surface reaction mechanism for steam reforming of methane over nickel catalyst T2 - Reaction Kinetics, Mechanisms and Catalysis KW - Nickel-based catalyst KW - Kinetic consistency KW - Thermodynamic analysis KW - Steam reforming KW - Detailed surface reaction mechanism Y1 - 2022 UR - https://link.springer.com/article/10.1007/s11144-022-02314-7 U6 - https://doi.org/10.1007/s11144-022-02314-7 SN - 1878-5204 SN - 1878-5190 VL - 135 IS - 6 SP - 3059 EP - 3083 ER - TY - GEN A1 - Franken, Tim A1 - Rachow, Fabian A1 - Charlafti, Evgenia A1 - Flege, Jan Ingo A1 - Jenssen, Martin A1 - Verma, Rakhi A1 - Günther, Vivien A1 - Mauss, Fabian T1 - Numerical investigation of oxy-methane combustion for stationary engines T2 - 40th International Symposium on Combustion N2 - This work presents a numerical investigation of turbulent oxyfuel combustion of methane in a gas engine with passive pre-chamber. The experimental data of a motored operating point at 1600 rpm and natural gas fired operating point at 2450 rpm, 6 bar IMEP and λ=1.5 are provided by TU Freiberg to validate the simulation model. The performance of the detailed chemistry model of Shrestha et al. predicting laminar burning velocity of premixed methane-oxygen flames is evaluated using the experiments of Mouze-Mornettas et al. The detailed chemistry model predicts the laminar flame speed within an accuracy range of ±10% for elevated pressure, temperature, and different equivalence ratios. For predicting the turbulent combustion in the gas engine, a three-dimensional (3D) Large Eddy Simulation (LES) with G Equation model and laminar flame speed look-up tables is used. The chemistry in the unburnt and burnt gas is solved using a constant volume detailed chemistry solver. The 3D LES model shows a good match of the motored and natural gas fired in-cylinder pressure profile. Subsequently the fuel is switched to methane and oxygen is used as oxidizer. The 3D LES results show an increase of maximum cylinder pressure up to 100 bar for λ=1.5, and the turbulent flame regime is shifted towards high Damköhler numbers compared to combustion with air. Diluting the cylinder gas with 50 mole-% CO2 or 65 mole-% H2O shows a significant reduction of peak cylinder pressure, and lower Damköhler and higher Karlovitz numbers compared to methane-oxygen combustion. KW - Oxyfuel KW - Simulation KW - Engines Y1 - 2024 ER - TY - GEN A1 - Verma, Rakhi A1 - Günther, Vivien A1 - Charlafti, Evgenia A1 - Rachow, Fabian A1 - Giri, Binod Raj A1 - Hemaizia, Abdelkader A1 - Thévenin, Dominique A1 - Flege, Jan Ingo A1 - Mauss, Fabian T1 - Development of detailed surface reaction mechanism for methanation process based on experiments T2 - Proceedings in applied mathematics and mechanics : PAMM N2 - The pressure to reduce greenhouse gas emissions is growing, which demands new and innovative technologies to produce mobile as well as stationary energy. The methanation offers a pathway to reduce greenhouse gas emissions by directly converting to . This also plays a crucial role in “power‐to‐gas” (P2G) technologies by providing an approach to store excess renewable energy in the form of methane in an existing natural gas infrastructure. However, methanation is a complex process due to its exothermic nature, interaction of the gas species with the catalyst, and possible catalyst degradation. Therefore, a deeper understanding is required for the methanation reaction, its different reaction pathways, and side reactions. In this work, we aim to understand the direct production of synthetic natural gas from and in a Sabatier process with the help of experiments over a Ni/ catalyst. A detailed surface reaction mechanism is developed to extend the study numerically by validating the simulation results with the experimental data. A one‐dimensional model, LOGEcat, based on a single‐channel catalyst model, is used for kinetic modeling. Experiments as well as simulations have been performed at various conditions, such as temperature variation and dilution to the inlet composition. We have successfully captured the experimental trends using the kinetic model developed for the conditions considered for the analysis. Y1 - 2026 U6 - https://doi.org/10.1002/pamm.70061 SN - 1617-7061 VL - 26 IS - 1 SP - 1 EP - 6 PB - Wiley CY - Weinheim ER - TY - GEN A1 - Verma, Rakhi A1 - Günther, Vivien A1 - Giri, Binod Raj A1 - Hemaizia, Abdelkader A1 - Thévenin, Dominique A1 - Mauss, Fabian T1 - Kinetic modeling of CO₂ methanation for methane production : a comprehensive study T2 - IFAC-PapersOnLine N2 - 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. Y1 - 2025 U6 - https://doi.org/10.1016/j.ifacol.2025.12.175 SN - 2405-8963 VL - 59 IS - 29 SP - 18 EP - 23 PB - Elsevier BV CY - Amsterdam ER - TY - GEN A1 - Verma, Rakhi A1 - Günther, Vivien A1 - Giri, Binod Raj A1 - Mauss, Fabian T1 - Effect of pressure and nitrogen dilution on surface species and reaction kinetics in CO₂ methanation over Ni catalyst T2 - IFAC-PapersOnLine N2 - 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. KW - Kinetic modeling KW - CO₂ methanation KW - Sabatier reaction KW - Power to gas (P2G) KW - Synthetic natural gas (SNG) Y1 - 2025 U6 - https://doi.org/10.1016/j.ifacol.2025.12.172 SN - 2405-8963 VL - 59 IS - 29 SP - 1 EP - 5 PB - Elsevier BV CY - Amsterdam ER -