Enhancing Ammonia Combustion in Heavy-Duty SI Engines: A 3D-CFD Study on Pre-Chamber Ignition, Methane Addition, and Spark Timing Optimization

Ammonia shows great potential as a zero-carbon fuel for internal combustion engines, but its low flame speed and heat of combustion present challenges for efficient operation. The pre-chamber spark-ignition (PCSI) system offers a promising solution by creating multiple ignition points in the main chamber, enhancing combustion efficiency while enabling lean-burn operation. This study numerically investigates the combustion characteristics and emissions of an active PCSI heavy-duty engine fueled with ammonia and ammonia-methane mixtures using 3D-CFD simulations. Methane, with its higher flame speed, improves combustion propagation and engine performance when mixed with ammonia. A newly developed chemical kinetics mechanism is used to study the interaction between the two fuels. The simulations begin with a methane-fueled case validated against experimental data, followed by an exploration of various ammonia-methane blends. A detailed spark advance (SA) analysis is performed, with SA varied between 14° and 50° BTDC, to determine optimal ignition timing for each blend in terms of both performance and emissions. The results highlight that the optimal configuration occurs with the pre-chamber fully fueled by methane and the main chamber operating with a 50% NH₃ – 50% CH₄ mixture at a SA of 38° BTDC. These findings contribute to the advancement of heavy-duty spark-ignition engines toward higher efficiency and reduced environmental impact, supporting compliance with stringent emissions regulations.