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

Ammonia is a promising fuel for achieving zero-carbon emissions in internal combustion engines. However, its low flame speed and heat of combustion pose significant challenges for efficient combustion. The pre-chamber (PC) spark-ignition (SI) system offers a viable solution by generating multiple ignition points in the main chamber (MC), enhancing combustion efficiency and enabling at the same time lean-burn operation. This study investigates the combustion characteristics and emissions of an active PC spark-ignition heavy-duty engine fueled with ammonia and ammonia-methane mixtures through numerical 3D-CFD simulations performed using the CONVERGE software. These simulations provide an accurate representation of the complex chemical and physical phenomena occurring within the combustion chamber. The study starts from a fully methane-fueled case, validated against experimental data, and subsequently explores different ammonia-methane mixtures. Then, a detailed spark timing (ST) analysis is conducted, varying the ST from 14° to 50° BTDC, to determine the optimal ignition timing for each fuel blend in terms of both performance and emissions. The findings contribute to the ongoing efforts to improve the efficiency and environmental sustainability of heavy-duty spark-ignition engines, aligning with increasingly stringent emissions regulations. The results indicate that optimal performance is achieved with the PC entirely fueled by methane and the MC operating with a 80% NH₃ – 20% CH₄ mixture, with a ST of 38° BTDC.