@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{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{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{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{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{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{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{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} }