Assessment of the co-combustion process of ammonia with hydrogen in a research VCR piston engine

The presented work concerns experimental research of a spark-ignition engine with variable compression ratio (VCR), adapted to dual-fuel operation, in which co-combustion of ammonia with hydrogen was conducted, and the energy share of hydrogen varied from 0% to 70%. The research was aimed at assessing the impact of the energy share of hydrogen co-combusted with ammonia on the performance, stability and emissions of an engine operating at a compression ratio of 8 (CR 8) and 10 (CR 10). The operation of the engine powered by ammonia alone, for both CR 8 and CR 10, is associated with either a complete lack of ignition in a significant number of cycles or with significantly delayed ignition and the related low value of the maximum pressure p_max. Increasing the energy share of hydrogen in the fuel to 12% allows to completely eliminate the instability of the ignition process in the combustible mixture, which is confirmed by a decrease in the IMEP uniqueness and a much lower p_max dispersion. For 12% of the energy share of hydrogen co-combusted with ammonia, the most favorable course of the combustion process was obtained, the highest engine efficiency and the highest IMEP value were recorded. The conducted research shows that increasing the H₂ share causes an increase in NO emissions, for both analyzed compression ratios.