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 H 2 share causes an increase in NO emissions, for both analyzed compression ratios. • For 8 and 10 compression ratios, 12% of hydrogen energy share co-fired with ammonia provided the most favorable. • The engine powered with ammonia alone results in a very high IMEP uniqueness (COV IMEP >5%). • Compared to powering engine by ammonia, 12% of H2 fraction causes 2 times decrease of the ignition delay. • An increase in the proportion of hydrogen causes an increase in NO emissions. • The increase in H2 fraction burned with ammonia requires a reduction in the ignition timing. [ABSTRACT FROM AUTHOR]