Effect of intake air temperature on combustion characteristics and operation range of high-pressure ammonia direct injection engine

Ammonia is emerging as a promising carbon-free fuel, particularly for internal combustion engines, due to its high hydrogen content and potential for sustainable production. However, ammonia's low flame speed and narrow flammability limit pose challenges to combustion stability and efficiency, necessitating research into strategies. This study investigates the effects of intake air temperature control on the combustion characteristics of a direct-injection ammonia-fueled spark-ignition engine. Experiments were conducted at engine speeds of 1000 rpm and 1500 rpm under varying load conditions, focusing on combustion stability, thermal efficiency, and emissions. The results indicate that increasing intake air temperature enhances combustion stability at lower engine loads by reducing ignition delay and improving fuel-air mixing. Elevated intake air temperatures resulted in increased NOx emissions due to higher peak combustion temperatures. Unburned NH3 emissions correlated with efficiency losses, increasing significantly at higher loads.