Experimental and kinetic study on the laminar premixed ammonia/n-propanol flames at elevated temperatures and pressures

Alcohols generated from renewable energy can be used as a combustion enhancer for ammonia so the carbon neutrality of burning ammonia can be retained. This study measured the laminar burning velocity of ammonia with n-propanol addition (0, 20%, 50% and 100%) in a constant volume combustion chamber at elevated temperatures up to 473 K and pressures ranging from 1 to 5 atm. It was found that adding n-propanol and increasing the initial temperature both can significantly increase the laminar burning velocity of ammonia whereas increasing initial pressure results in slower laminar burning velocity. Flame morphology shows that flames wrinkles are promoted at richer flames and higher pressures indicating intensified flame instability at these conditions. A compact ammonia/n-propanol mechanism was developed and validated in this study, which can accurately reproduce the measured laminar burning velocities. Kinetic analysis shows that n-propanol promotes ammonia combustion by increasing the radical pool. With 20% n-propanol, both ammonia and n-propanol oxidation are important for controlling laminar burning velocity, while with 50% n-propanol, the laminar burning velocity is prominently controlled by n-propanol oxidation. NOx analysis implies that NO emission has non-monotonic relationship with n-propanol addition and HNO is an important precursor for NO formation.