Effects of Ammonia on Cycle-by-Cycle Variations in a Spark Ignition Engine Fueled with Hydrogen

Abstract

Hydrogen and its compound ammonia are set to have an important share in the future global energy structure. The co-combustion of hydrogen and ammonia leverages their complementary strengths, aligning with the push for cleaner and more efficient internal combustion engines. Most current research uses ammonia as the primary fuel, exploring hydrogen's role as a combustion promoter. There are few studies focusing on hydrogen as the primary fuel and ammonia as an inhibitor. Thus, this paper investigates the effects of ammonia on cyclic variations in a hydrogen-fueled spark ignition engine. We analyzed the combustion characteristics under stoichiometric and lean conditions while varying the ammonia energy ratio (ER) from 0 to 65%. The results showed that when increasing ammonia ER, the fluctuation of pmax gradually increased while the average values of pmax and (dp/dφ)max decrease. Linear relationships between pmax and (dp/dφ)max and their respective crank angles were detected when spark timing was optimized under both stoichiometric and lean conditions. With an increase in ammonia ER, the mean value of IMEP rose, especially at higher ER levels, and the changes in IMEP between any two consecutive cycles also increased. The addition of ammonia was found to increase cyclic variations, although it showed greater tolerance to ammonia under lean burn conditions in the tested hydrogen engine.

Keywords: hydrogen, Ammonia, primary fuel, combustion promoter, spark ignition engine, Hydrogen engine