Ammonia-Hydrogen Combustion in a Heavy-Duty Diesel Engine Converted to Spark Ignition Operation

Ammonia is a carbon-free fuel alternative for the internal combustion engine decarbonization. However, its toxicity and less advantageous combustion characteristics including higher nitrogen-based engine-out emissions have delayed its use in power generation applications. Therefore, the use of a secondary and also carbon-free fuel such as hydrogen was proposed in the literature as a solution to promote and improve ammonia combustion while minimizing any modifications in engine parameters and control strategy that may be required when compared to using conventional hydrocarbon-based fuels. In addition, the higher resistance to autoignition of ammonia can allow operation at higher compression ratios in spark ignition applications, therefore increasing the thermal efficiency. The study presented here used a single-cylinder heavy-duty research engine converted to spark ignition operation to investigate medium load engine operation with ammonia-hydrogen blends in which hydrogen represented 30% to 60% of the total energy in the fuel blend, at an engine speed of 1000 rpm and an equivalence ratio of 0.8. To find the maximum brake torque (MBT) for each fuel blend, spark timing varied from 35 CAD to -5 CAD ATDC. Then, the effect of energy substitution ratio (defined as the ratio of the hydrogen energy to the total fuel blend energy) on engine performance (i.e., in-cylinder pressure data, apparent heat release rate, and indicated mean effective pressure) was analyzed. Results indicated that retarding the spark timing by 5 CAD was required to achieve the optimum IMEP every time ESR increased by 0.1. Then, hydrogen addition decreased the ignition delay and combustion duration by 37% and 20%, respectively, as ESR increased from 0.3 to 0.6. However, higher hydrogen fractions inside affected the combustion phasing in a negative way, therefore affecting the engine performance at the operating conditions investigated in this work.