Optical Investigation and combustion Analysis of Stratified Ammonia-hydrogen Pre-chamber Engine with Variable Injection Timing

This study presents an experimental investigation of a direct injection ammonia-fuelled engine using hydrogen pre-chamber jet ignition. All tests have been conducted in an optically accessible combustion chamber that is installed in the head of a single-cylinder engine. The effect of ammonia injection timing on ignition and combustion characteristics was investigated, with the timing varied from 165 CAD BTDC to 40 CAD BTDC. The experiments were conducted with a fixed spark timing of 14 CAD BTDC while ammonia injection duration was adjusted to maintain a main chamber global equivalence ratio of 0.6. Two pre-chamber nozzle configurations, a single-hole and a multi-hole, were tested. The results show that the later NH3 injection timing (40 CAD BTDC) significantly improved combustion, with a peak in-cylinder pressure of 80 bar measured compared to a peak in-cylinder pressure of 50 bar with earlier injection (165 CAD BTDC). This study indicates the importance of optimising ammonia injection timing in order to enhance combustion stability and efficiency. The hydrogen pre-chamber jet ignition, combined with a late ammonia injection is a promising approach for addressing the combustion challenges of ammonia as a zero-carbon fuel for maritime applications.