TY - GEN A1 - Shrestha, Krishna Prasad A1 - Eckart, Sven A1 - Elbaz, Ayman M. A1 - Giri, Binod Raj A1 - Fritsche, Chris A1 - Seidel, Lars A1 - Roberts, William L. A1 - Krause, Hartmut A1 - Mauß, Fabian T1 - A comprehensive kinetic model for dimethyl ether and dimethoxymethane oxidation and NOx interaction utilizing experimental laminar flame speed measurements at elevated pressure and temperature T2 - Combustion and Flame N2 - Laminar flame speeds of dimethyl ether and dimethoxymethane at pressures from 1 to 5 bar and initial temperatures from 298 to 373 K were determined experimentally using a constant volume spherical vessel and a heat flux burner setup. This study is the first to report dimethoxymethane laminar flame speeds at a pressure higher than 1 bar. Using these experimental data along with data available in the literature, a new kinetic model for the prediction of the oxidation behavior of dimethyl ether and dimethoxymethane in freely propagating and burner stabilized premixed flames, in shock tubes, rapid compression machines, flow reactors, and a jet-stirred reactor has been developed. The experimental results from the present work and literature are interpreted with the help of the derived kinetic model. This newly developed reaction mechanism considers the redox chemistry of NOx to accommodate the influence of the oxygen level on the onset of fuel conversion and interconversion of NO and NO2. The current model suggests that an increased O2 level promotes the HO2 production, which in turn leads to the formation of OH radicals, which promotes the combustion of the fuel/air mixture under lean conditions. The increase of OH radical concentrations is mainly via the NO/NO2 interconversion reaction channel, NO+HO2=NO2+OH, NO2+H=NO+OH, CH3OCH3+NO2=CH3OCH2+HONO, followed by the thermal decomposition of HONO. This work extends the kinetic database and helps to improve the understanding of dimethyl ether and dimethoxymethane combustion behavior. The kinetic model presented in this work can serve as a base model for hydrocarbons and oxygenated fuels higher than C2. KW - Dimethyl ether KW - Dimethoxymethane KW - Laminar flame speed KW - Kinetic modeling KW - NOx Y1 - 2020 U6 - https://doi.org/10.1016/j.combustflame.2020.04.016 SN - 1556-2921 VL - 218 SP - 57 EP - 74 ER - TY - GEN A1 - Shrestha, Krishna Prasad A1 - Lhuillier, Charles A1 - Barbosa, Amanda Alves A1 - Brequigny, Pierre A1 - Contino, Francesco A1 - Mounaïm-Rousselle, Christine A1 - Seidel, Lars A1 - Mauß, Fabian T1 - An experimental and modeling study of ammonia with enriched oxygen content and ammonia/hydrogen laminar flame speed at elevated pressure and temperature T2 - Proceedings of the Combustion Institute N2 - Laminar flame speeds of ammonia with oxygen-enriched air (oxygen content varying from 21 to 30 vol.%) and ammonia-hydrogen-air mixtures (fuel hydrogen content varying from 0 to 30 vol.%) at elevated pressure (1–10 bar) and temperature (298–473 K) were determined experimentally using a constant volume combustion chamber. Moreover, ammonia laminar flame speeds with helium as an inert were measured for the first time. Using these experimental data along with published ones, we have developed a newly compiled kinetic model for the prediction of the oxidation of ammonia and ammonia-hydrogen blends in freely propagating and burner stabilized premixed flames, as well as in shock tubes, rapid compression machines and a jet-stirred reactor. The reaction mechanism also considers the formation of nitrogen oxides, as well as the reduction of nitrogen oxides depending on the conditions of the surrounding gas phase. The experimental results from the present work and the literature are interpreted with the help of the kinetic model derived here. The experiments show that increasing the initial temperature, fuel hydrogen content, or oxidizer oxygen content causes the laminar flame speed to increase, while it decreases when increasing the initial pressure. The proposed kinetic model predicts the same trends than experiments and a good agreement is found with measurements for a wide range of conditions. The model suggests that under rich conditions the N2H2 formation path is favored compared to stoichiometric condition. The most important reactions under rich conditions are: NH2+NH=N2H2+H, NH2+NH2=N2H2+H2, N2H2+H=NNH+H2 and N2H2+M=NNH+H+M. These reactions were also found to be among the most sensitive reactions for predicting the laminar flame speed for all the cases investigated. KW - Ammonia KW - Laminar flame speed KW - Kinetic modeling KW - Ammonia-hydrogen KW - NOx Y1 - 2020 UR - https://www.sciencedirect.com/science/article/pii/S1540748920302881#! U6 - https://doi.org/10.1016/j.proci.2020.06.197 SN - 1540-7489 VL - 2020 SP - 1 EP - 12 ER - TY - GEN A1 - Shrestha, Krishna Prasad A1 - Seidel, Lars A1 - Zeuch, Thomas A1 - Moréac, Gladys A1 - Dagaut, Philippe A1 - Mauß, Fabian T1 - On the implications of nitromethane – NOx chemistry interactions for combustion processes T2 - Fuel N2 - In this work, we report a detailed investigation of the CH3NO2 chemistry effect on fuel-NO interactions for the fuels methane and n-heptane using a recently developed and extensively validated H2/O2/CO/NOx/NH3/CH3NO2 baseline chemistry. In general, the model predictions show good agreement with temperature profiles of major and intermediate species in jet-stirred reactor experiments and they capture the subtle effect of NO addition. For both fuels, the CH3NO2 kinetics retard the system reactivity in the low temperature range by delaying the production of key radicals like OH and HO2. This explains the retarding effect of NO for n-heptane low temperature ignition and the overprediction of reactivity enhancement by NO in earlier studies on methane combustion. For methane, the recently explored roaming mediated dissociation channel of CH3NO2 to CH3O + NO is a major reaction pathway for CH3NO2 consumption. Our analysis suggests that at higher pressure, relevant to engine conditions, the two key intermediate species HONO and CH3NO2 feature strongly increased concentrations during n-heptane combustion and they may be detectable under such conditions in combustion experiments of this fuel-NOx system. The results of this work call for detailed future investigations of the CH3NO2 chemistry effect in the context of exhaust gas recirculation, also with regard to the suppression of engine knock. KW - Nitromethane KW - NOx KW - Fuel-NOx KW - Kinetic modeling KW - EGR Y1 - 2021 UR - https://www.sciencedirect.com/science/article/pii/S001623612032857X#! U6 - https://doi.org/10.1016/j.fuel.2020.119861 SN - 0016-2361 VL - 289 ER - TY - GEN A1 - Shrestha, Krishna Prasad A1 - Giri, Binod Raj A1 - Adil, Mohammad A1 - Seidel, Lars A1 - Zeuch, Thomas A1 - Farooq, Aamir A1 - Mauß, Fabian T1 - Detailed Chemical Kinetic Study of Acetaldehyde Oxidation and Its Interaction with NOx T2 - Energy & fuels N2 - This work entails a detailed modeling and experimental study for the oxidation kinetics of acetaldehyde (CH3CHO) and its interaction with NOx. The ignition behavior of CH3CHO/O2/Ar has been investigated in a shock tube over the temperature range of 1149 to 1542 K, with equivalence ratios of 0.5 and 1.0 and pressures near 1.2 bar. Absorbance−time profiles of acetaldehyde were recorded using a mid-IR laser during the autoignition measurements. A comprehensive kinetic model has been developed to quantitatively predict the oxidation of acetaldehyde and its interaction with NOx. The kinetic model has been validated using experimental data of this work and available literature data from shock tube, plug flow, and jet-stirred reactors, freely propagating, and burner-stabilized premixed flames. For better accuracy of the kinetic model, the thermochemistry of 14 important species in the acetaldehyde submechanism was calculated using ab initio methods. The heat of formation of these species was computed using atomization and isodesmic reaction schemes. For the first time, this modeling study examines the effect of NO on acetaldehyde oxidation behavior over a wide range of experimental conditions. In most cases, the proposed kinetic model captures the experimental trends remarkably well. Interestingly, the doping of NO in CH3CHO did not perturb the NTC behavior of CH3CHO in contrast to other fuels, such as n-heptane and dimethyl ether. However, for flow reactor conditions at 1 atm, doping with 504 ppm of NO was found to promote the reactivity of acetaldehyde by lowering the onset temperature for CH3CHO oxidation by ∼140 K. The hydroxyl radical is the main cause of this shift, which originates from the NO + HO2 = OH + NO2 reaction. Further evolution of hydroxyl radicals occurs via the “NO−NO2” looping mechanism and expedites the reactivity of the system. This experimental and modeling work sheds new light on acetaldehyde oxidation behavior and its interaction with NOx under combustion-relevant conditions. KW - NOx KW - Kinetic modeling KW - Acetaldehyde KW - Ignition delay time Y1 - 2021 UR - https://pubs.acs.org/doi/10.1021/acs.energyfuels.1c01948?ref=pdf U6 - https://doi.org/10.1021/acs.energyfuels.1c01948 SN - 1520-5029 SN - 0887-0624 VL - 35 IS - 18 SP - 14963 EP - 14983 ER - TY - GEN A1 - Shrestha, Krishna Prasad A1 - Giri, Binod Raj A1 - Seidel, Lars A1 - Farooq, Aamir A1 - Mauß, Fabian T1 - A Kinetic Modeling Study for the Effect of NOx on Oxymethylene ethers (OMEn, n = 0 and 1) oxidation T2 - 10th European Combustion Meeting, Neapel N2 - We present a detailed kinetic model for the oxidation of dimethyl ether (OME0) and dimethoxymethane (OME1) in presence of NOx. We further explored the effect of NOx chemistry on the oxidation kinetics of the two OMEs. Our kinetic model is validated against the recent flow reactor data from Zhang et al. (Combust. Flame. 224 (2021) 94– 107). The results indicated that NO doping severely alters the oxidation kinetics of both fuels. The onset temperature for total fuel consumption is significantly shifted to lower temperatures for both fuels, which is in line with the experimental observation. We found that the addition of NO significantly inhibited the NTC behaviour of dimethyl ether. This inhibiting effect appears to stem from the competition between CH3OCH2O2 radical consumption by NO directly and the isomerization/dissociation reactions of CH3OCH2O2. Unlike dimethyl ether, dimethoxymethane does not exhibit a strong NTC behavior, and NO addition completely inhibited its weak NTC behavior. KW - DME KW - DMM KW - Oxymethylene ethers KW - NOx KW - Kinetic Modeling Y1 - 2021 UR - https://www.researchgate.net/publication/353620538_A_Kinetic_Modeling_Study_for_the_Effect_of_NOx_on_Oxymethylene_ethers_OMEn_n_0_and_1_oxidation CY - Neapel ER -