Numerical Study on the Combustion Characteristics of an Ammonia/Hydrogen Engine with Active Prechamber Ignition

Both ammonia and hydrogen, as zero-carbon fuels for internal combustion engines, are received growing attention. However, ammonia faces a challenge of low flame propagation velocity. Through injecting hydrogen into active pre-chamber, its jet flame ignition can accelerate the flame propagation velocity of ammonia. The influence of different pre-chamber structures on engine combustion characteristics is significant. In this paper, numerical studies were conducted to assess the impact of various pre-chamber structures and hydrogen injection strategy on the combustion characteristics of ammonia/hydrogen engines while maintaining the equivalent ratio of 1.0. The results indicate that the jet angle significantly affects the position of jet flame and the followed main combustion. The in-cylinder combustion pressure peaks at jet angle of 150°. Meanwhile, the combustion duration of 150° is shortened by 74.3% compared with that of 60°. When the jet angle is 160°, the flame jet is positioned too far up into the slit between the cylinder head and the piston, resulting in a deteriorated combustion. Among the different numbers of pre-chamber jets, the combustion characteristics of the structure with 6 jets is the best. The diameter of the pre-chamber jet has less influence on the combustion. The effect of hydrogen injection on combustion was studied by employing the optimized pre-chamber structure. Misfire occurs when the hydrogen injection timing is -30 °CA ATDC. Advancing the injection timing can avoid the misfire, and is favorable for hydrogen to form the mixture, thus accelerating the combustion speed in the main combustion chamber. When the hydrogen ratio increases from 5.0% to 20.0%, the combustion duration is shortened from 19.2°CA to 5.1°CA.