Design and optimisation of pre-chamber ignition system for heavy-duty hydrogen engine at lean conditions

Strict regulations and legislation for carbon emissions and pollution from heavy-duty engines are pushing towards carbon-free fuels such as Hydrogen as a fuel for internal combustion engines. Moving towards this goal, the engine design needs to fully comply with Hydrogen’s unique characteristics to achieve optimum performance and efficiency. One of the aspects that has the potential to improve combustion efficiency and emissions is adopting the pre-chamber ignition strategy in large bore engines at lean conditions. The pre-chamber is a small cavity, usually 3-6% of the total engine volume, installed on the cylinder head, housing the initial combustion event, which would then be injected into the main chamber via nozzles placed at the bottom of the pre-chamber. This ignition strategy would provide multiple flame fronts into the main chamber, accelerating combustion speed and enhancing engine performance. However, the pre-chamber must be designed dedicatedly for Hydrogen combustion to make the best use of this strategy. In this paper, we aimed to investigate the effects of pre-chamber designs such as throat diameter, number of nozzle holes, injection direction and nozzle diameter on the combustion development in the pre-chamber and, consequently, the combustion in the main chamber along with the engine performance and efficiency of a 2 L single-cylinder heavy-duty engine. The simulations are performed in Star-CD software. This research shows an optimum pre-chamber throat diameter and nozzle number/diameter configuration, which significantly affects engine performance. Throat diameters narrower than the optimum value will slow down the flame development inside the pre-chamber, followed by rapid flame quenching, while wider throat diameters wouldn’t fully use the pre-chamber capabilities for flame development and injection into the main chamber. It was shown that optimum pre-chamber design configuration could significantly improve thermal efficiency, and thus, dedicated pre-chamber design is critical to achieving optimal performance.