An experimental and kinetic modeling study of ammonia/n-heptane blends

Ammonia is carbon free and hence is a promising renewable fuel to achieve a reduction in CO2 emis-sions. However, due to its relatively low reactivity, ammonia is often blended with other high reac-tivity fuels in practical combustors. This study aims to understand the chemical kinetics of ammonia blended with n-heptane, which is a primary reference fuel and an important component in diesel and gasoline surrogate models. A high-pressure shock tube is used to measure the ignition delay times of ammonia/ n-heptane blends with different blending ratios, for stoichiometric mixtures at 10 atm pres-sure in the temperature range 10 0 0-140 0 K. The experimental results show that fuel reactivity de-creases with increasing ammonia concentration. The oxygen concentration also shows a large effect on the reactivity of ammonia/ n-heptane blends. A new detailed kinetic model is developed to simu-late these new ignition delay times in addition to experimental data available in the literature. Overall, the current kinetic model can predict well the auto-ignition behavior and laminar burning velocities of ammonia/ n-heptane blends over a wide range of experimental conditions. Flux and sensitivity analyzes show that the interaction reaction pathways between ammonia and n-heptane via H-atom abstraction from n-heptane by NH2 radicals are important in predicting the fuel reactivity of ammonia/ n-heptane blends.(c) 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

This study investigates the chemical kinetics of ammonia blended with n-heptane fuel and develops a detailed kinetic model to predict the combustion behavior. The results show that increasing ammonia concentration decreases fuel reactivity, and the interaction between ammonia and n-heptane via H-atom abstraction is important in predicting the fuel reactivity.