TY - GEN A1 - Issayev, Gani A1 - Giri, Binod Raj A1 - Elbaz, Ayman M. A1 - Shrestha, Krishna Prasad A1 - Mauß, Fabian A1 - Roberts, William L. A1 - Farooq, Aamir T1 - Combustion behavior of ammonia blended with diethyl ether T2 - Proceedings of the Combustion Institute N2 - Ammonia (NH3) is recognized as a carbon-free hydrogen-carrier fuel with a high content of hydrogen atoms per unit volume. Recently, ammonia has received increasing attention as a promising alternative fuel for internal combustion engine and gas turbine applications. However, the viability of ammonia fueling future combustion devices has several barriers to overcome. To overcome the challenge of its low reactivity, it is proposed to blend it with a high-reactivity fuel. In this work, we have investigated the combustion characteristics of ammonia/diethyl ether (NH3/DEE) blends using a rapid compression machine (RCM) and a constant volume spherical reactor (CVSR). Ignition delay times (IDTs) of NH3/DEE blends were measured using the RCM over a temperature range of 620 to 942 K, pressures near 20 and 40 bar, equivalence ratios (Φ) of 1 and 0.5, and a range of mole fractions of DEE, χDEE, from 0.05 to 0.2 (DEE/NH3 = 5 – 20%). Laminar burning velocities of NH3/DEE premixed flames were measured using the CVSR at 298 K, 1 bar, Φ of 0.9 to 1.3, and χDEE from 0.1 to 0.4. Our results indicate that DEE promotes the reactivity of fuel blends resulting in significant shortening of the ignition delay times of ammonia under RCM conditions. IDTs expectedly exhibited strong dependence on pressure and equivalence ratio for a given blend. Laminar burning velocity was found to increase with increasing fraction of DEE. The burnt gas Markstein length increased with equivalence ratio for χDEE = 0.1 as seen in NH3-air flames, while the opposite evolution of Markstein length was observed with Φ for 0.1 < χDEE ≤ 0.4, as observed in isooctane-air flames. A detailed chemical kinetics model was assembled to analyze and understand the combustion characteristics of NH3/DEE blends. KW - Ammonia KW - Diethyl ether KW - Ignition delay times KW - Laminar flame speed Y1 - 2020 U6 - https://doi.org/10.1016/j.proci.2020.06.337 SN - 1540-7489 VL - 38 (2021) IS - 1 SP - 499 EP - 506 ER - TY - GEN A1 - Elbaz, Ayman M. A1 - Giri, Binod Raj A1 - Issayev, Gani A1 - Shrestha, Krishna Prasad A1 - Mauß, Fabian A1 - Farooq, Aamir A1 - Roberts, William L. T1 - Experimental and Kinetic Modeling Study of Laminar Flame Speed of Dimethoxymethane and Ammonia Blends T2 - Energy & Fuels N2 - Ammonia (NH3) is considered a promising carbon-neutral fuel, with a high hydrogen content, that can diversify the global energy system. Blending ammonia with a highly reactive fuel is one possible strategy to enhance its combustion characteristics. Here, an investigation of blends of NH3 and dimethoxymethane (DMM), a biofuel with high fuel-born oxygen content and no carbon–carbon bonds, is reported. Unstretched laminar burning velocity (SL) and Markstein length of different NH3/DMM blends were experimentally determined using spherically propagating premixed flames. The DMM mole fraction was varied from 0.2 to 0.6 while measuring SL at 298 K, 0.1 MPa, and equivalence ratios (Φ) over the range of 0.8–1.3. The addition of DMM was found to immensely enhance the combustion characteristics of ammonia. DMM 20% (by mole fraction) in the NH3/DMM blend increased SL by more than a factor of 3 over neat ammonia; such enhancement was found to be comparable to 60% CH4 in NH3 (Φ = 0.9–1.1) blends. Increasing Φ was found to significantly decrease the burned gas Markstein length for lean cases, whereas a negligible effect was observed for rich mixtures. A composite chemical kinetic model of DMM/NH3, aimed at interpreting the high-temperature combustion chemistry, was able to reliably predict SL for neat NH3 and DMM flames. Also, the predictive capability of the kinetic model to describe SL for DMM/NH3 blends is reasonably good. Sensitivity analysis and reaction path analysis indicated that the NH3/DMM blends could be understood as dual oxidation processes of the individual fuels that are competing for the same radical pool. KW - Ammonia KW - Dimethoxymethane KW - Laminar flame speed KW - Kinetic modeling Y1 - 2020 UR - https://pubs.acs.org/doi/abs/10.1021/acs.energyfuels.0c02269 U6 - https://doi.org/10.1021/acs.energyfuels.0c02269 SN - 1520-5029 VL - 34 IS - 11 SP - 14727 EP - 14740 ER - TY - GEN A1 - Issayev, Gani A1 - Giri, Binod Raj A1 - Elbaz, Ayman M. A1 - Shrestha, Krishna Prasad A1 - Mauß, Fabian A1 - Roberts, William L. A1 - Farooq, Aamir T1 - Ignition delay time and laminar flame speed measurements of ammonia blended with dimethyl ether: A promising low carbon fuel blend T2 - Renewable Energy N2 - Ammonia (NH3) has recently received much attention as a promising future fuel for mobility and power generation. The use of ammonia as a fueling vector can help curb global warming by cutting CO2 emissions because it is a carbon-free fuel and a hydrogen carrier with a high percentage of hydrogen atoms per unit volume. Liquid ammonia contains a higher volumetric density of hydrogen than liquid hydrogen. The low reactivity of ammonia, however, hinders its direct usage as a combustible fuel. One feasible way to boost the reactivity of ammonia is to target a dual-fuel system comprising of ammonia and a suitable combustion promoter. In this work, combustion properties of ammonia were investigated by blending it with various proportions of dimethyl ether (DME) using a rapid compression machine (RCM) and a constant volume spherical reactor (CVSR) over a wide range of experimental conditions. DME is a highly reactive fuel that may be produced in a sustainable carbon cycle with a net zero-carbon emission. Ignition delay times (IDTs) of NH3/DME blends were measured over a temperature (T) range of 649e950 K, pressures (P) of 20 and 40 bar, equivalence ratios (F) of 0.5 and 1 for a range of DME mole fractions (cDME) of 0.05e0.5 in the blends. In addition, the laminar burning velocities of NH3/DME blends were measured at P ¼ 1, 3 and 5 bar, F ¼ 0.8e1.3 and T ¼ 300 K for cDME ranging from 0.18 to 0.47. Our results suggest that DME is a good ignition promoter, resulting in a significant shortening of IDTs and an increase of flame speeds of NH3. A detailed chemical model has been developed and validated against the experimental data. Overall, our kinetic model offered reasonable predictive capabilities capturing the experimental trends over a wide range of conditions. In the worst-case scenario, our model underpredicted IDTs by a factor of ~2.5 while overpredicting laminar flame speed by ~20%. KW - DME KW - Lamianr flame speed KW - Ignition delay time KW - Kinetic modeling KW - Ammonia Y1 - 2022 UR - https://www.sciencedirect.com/science/article/pii/S0960148121014440?via%3Dihub#! U6 - https://doi.org/10.1016/j.renene.2021.09.117 SN - 1879-0682 VL - 181 SP - 1353 EP - 1370 ER - TY - GEN A1 - Shrestha, Krishna Prasad A1 - Giri, Binod Raj A1 - Elbaz, Ayman M. A1 - Issayev, Gani A1 - Roberts, William L. A1 - Seidel, Lars A1 - Mauß, Fabian A1 - Farooq, Aamir T1 - A detailed chemical insights into the kinetics of diethyl ether enhancing ammonia combustion and the importance of NOx recycling mechanism T2 - Fuel Communications N2 - In this work, we investigated the combustion characteristics of ammonia (NH3) by blending it with various proportions of diethyl ether (DEE). We measured laminar flame speed of various NH3/DEE blends (DEE, 10–40% by mole) using a constant volume spherical vessel at Ti = 298 K and Pi = 3 and 5 bar and Φ = 0.8–1.3. We developed a detailed kinetic model to describe the trends of the current and previously published experimental data. For the robustness of the model, we first developed a comprehensive diethyl ether kinetic mechanism to accurately characterize neat DEE oxidation behavior. We validated the kinetic model using a large pool of experimental data comprising shock tube, rapid compression machine, jet-stirred and flow reactors, freely propagating, and burner-stabilized premixed flames. The developed kinetic model performs remarkably in capturing the combustion behavior of pure DEE and NH3. Importantly, our model captures the experimental data of laminar flame speed and ignition delay times of various NH3/DEE blends over a wide range of conditions. We found that DEE is a promising candidate to promote the combustion characteristics of NH3. A small portion of DEE (10%) enhances the laminar flame speed of NH3 by a factor of 2 at Pi = 1 bar, Ti = 298 K, and Φ = 1.0. A further doubling of the DEE mole fraction to 20% did not enhance the laminar flame speed of NH3 with the same propensity. At low temperatures, adding 5% DEE in NH3 blend has significantly expedited the system reactivity by lowering the autoignition temperature. A further 5% increment of DEE (i.e., 10% DEE in NH3) lowers the autoignition temperature by ∼120 K to achieve the same ignition delay time. The “NOsingle bondNO2” looping mechanism predominantly drives such reactivity accelerating effect. Here, the reactions, NO + HO2 = NO2 + OH and NO2 + H = NO + OH, appear to enhance the reactive radical pool by generating OH radicals. We observed that the HNO path is favored more with increasing DEE content which eventually liberates NO. Other key reactions in “NOsingle bondNO2” looping mechanism are: CH3 + NO2 = CH3O + NO, CH3O2 + NO = CH3O + NO2, C2H5 + NO2 = C2H5O + NO, C2H5O2 + NO = C2H5O + NO2. In addition, CH3 + NH2(+M) = CH3NH2(+M) reaction is also one of the important cross-reactions which leads to the formation of HCN. Therefore, cross-reactions between the nitrogen and carbon family are crucial in accurately predicting autoignition timing. This work provides a detailed chemical insight into the NH3 and DEE interaction, which could be applied to other fuel blends of NH3. The kinetic model is also validated for several C1single bondC3 fuels including their interaction with NOx. KW - DEE KW - Ammonia KW - Kinetic Model KW - Laminar flame speed KW - Ignition delay time Y1 - 2022 U6 - https://doi.org/10.1016/j.jfueco.2022.100051 SN - 2666-0520 VL - 10 ER -