Shock tube and modeling study on autoignition properties of ammonia/ diethyl ether mixtures at high temperatures

Ammonia (NH3) can be used as a fuel in gas turbines and internal combustion engines. However, it exhibits a long ignition delay time (IDT), which could be reduced by mixing highly reactive fuels with it. Few studies have been conducted on the IDT by adding diethyl ether (DEE) as a reactive fuel to NH3 at high temperatures. Therefore, this study explores the influence of DEE on the autoignition characteristics and chemical kinetics of NH3 using experimental, simulation, and theoretical approaches. The IDT of NH3/DEE mixtures were measured using a shock tube considering DEE fractions of 0 %, 5 %, 10 %, and 30 %, equivalence ratios of 0.5, 1.0, and 2.0, pressures of 0.14 and 1.0 MPa, and temperatures of 1220-1980 K. A new NH3-DEE model was developed and validated against experimental data, reliably predicting the IDT. Chemical reaction kinetic analysis using this model reveals a nonlinear decrease in the IDT of NH3 with increasing DEE content, where adding only 5 % DEE reduced the IDT by over 80 %. The rapid consumption of DEE in the initial stages leads to the generation of numerous active radicals crucial for promoting NH3 combustion. With the increase in DEE content, the reaction flux of DEE consumed through H-abstraction reaction increases. Additionally, increasing the proportion of DEE increases the mole fraction of CH3 in the radical pool. This increase in CH3, when reacting with NH2, results in a higher concentration of cyanide, a highly toxic species.