Experimental and kinetic modeling study on auto-ignition properties of ammonia/ethanol blends at intermediate temperatures and high pressures

The auto-ignition properties of ammonia (NH3)/ethanol (C2H5OH) blends close to engine operating con-ditions were investigated for the first time. Specifically, the ignition delay times (IDT) of ammonia/ethanol blends were measured in a rapid compression machine (RCM) at elevated pressures of 20 and 40 bar, fiv e C2H5OH mole fractions from 0% to 100%, three equivalence ratios (& phi;) of 0.5, 1.0 and 2.0, and intermediate temperatures between 820 and 1120 K. The measurements reveal that ethanol can drastically promote the reactivity of ammonia, e.g., the auto-ignition temperature with merely 1% C 2 H 5 OH in fuel decreases accord-ingly around 110 K at 40 bar as compared to that of neat ammonia. Moreover, the promotion efficiency of ethanol is higher than hydrogen and methane with a factor of 5 and 10 under the same condition. Different dependences of IDT on the equivalence ratio were observed with different ethanol fractions in the blends, i.e., the IDTs of the 5%, 10% and 100% C2H5OH in fuel decrease with an increase of & phi;, but an opposite trend was observed in the mixture with 1% C2H5OH. A new chemical kinetic mechanism for NH3 /C2H5OH mixtures was developed and it is highlighted that the addition of cross-reactions between the two fuels is necessary to obtain reasonable simulations. Basically, the newly developed mechanism can reproduce the measurements of IDT very well, whereas it overestimates the reactivity of the stoichiometric and fuel-rich mixture with 1% C2H5OH in fuel. The sensitivity, reaction pathway, as well as rate of production analysis indicated that the ethanol addition to ammonia fuel blends provides key interaction pathways and enriches the O/H radical pool which further promotes the auto-ignition process.& COPY; 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

The auto-ignition properties of ammonia/ethanol blends under engine operating conditions were investigated. Ethanol was found to significantly promote the reactivity of ammonia, leading to a decrease in auto-ignition temperature. The new chemical kinetic mechanism developed for NH3/C2H5OH mixtures could accurately reproduce the ignition delay time measurement results. The addition of ethanol enriched the O/H radical pool and provided key interaction pathways to enhance the auto-ignition process.