Abstract
Ammonia is a promising alternative fuel, which is considered to have the potential to substitute conventional fossil fuels. In the present work, auto-ignition characteristics of ammonia substitution on methane are investigated both experimentally and numerically. The auto-ignition procedure of ammonia-substituted methane/air mixtures are measured behind the reflected shock wave in a shock tube experiment system over temperatures from 1355 to 1877 K, pressure up to 5 atm and an equivalence ratio from 0.5 to 2. Numerical simulation studies using a detailed kinetics mechanism are also performed to gain a deep insight into the auto-ignition procedure of ammonia-substituted methane fuel mixtures. The established numerical model is verified with the measured auto-ignition delay time data by experiments. Then, the auto-ignition delay times are predicted under a wider range of conditions such as equivalence ratio, pressure, temperature, etc. In this way, combustion characteristics of such mixtures are investigated. It is found that adding ammonia fuel to methane will not change the autoignition delay time of methane a lot, while it can effectively benefit the reduction of carbon emissions. Finally, sensitivity analyses are performed to provide essential information for the elementary reaction sensitive to the ignition characteristics. The results present in this work can provide fundamental information for combustion application of ammonia-based fuels.