Experimental Study on the Effect of Ammonia on Combustion and Emission Characteristics of a Spark Ignition Engine Fueled with Hydrogen

Using hydrogen and its compounds as fuel is one of the key ways to achieve zero carbon emissions in internal combustion engines. Due to the difference in fuel properties of hydrogen and ammonia, mixing the two can make up for each other's shortcomings in combustion performance. Therefore, this paper studies the effects of ammonia addition on the combustion and emission characteristics of a SI commercial hydrogen engine, and studies the differences in these effects under different excess air ratios. The results indicate that increasing the ammonia mass ratio lengthens both flame development and combustion duration, causing a delay in the combustion center. Under stoichiometric conditions, combustion instability increases, peak cylinder pressure and heat release rate decrease significantly, and exhaust temperatures rise. With a higher ammonia mass ratio, brake-specific fuel consumption first decreases and then increases, reaching a minimum at a 0.4-0.6 ammonia mass ratio. Unburned ammonia and N₂O emissions gradually increase, while NO <i>_X</i> emissions initially rise and then fall, peaking at a low ammonia mass ratio. From the perspective of balancing emissions and fuel economy, for hydrogen-ammonia mixed combustion engines, a 0.6 ammonia mass ratio is recommended under stoichiometric conditions, while lean burn conditions allow for a higher ammonia mass ratio.