Investigation of diesel pilot ignition strategy in a low-speed two-stroke marine hydrogen engine

This study investigates the combustion performance of a low-speed two-stroke marine hydrogen engine (LTMHE) operating with diesel pilot ignition. A skeletal hydrogen/primary reference fuel (PRF) chemical mechanism was developed and validated using ignition delay time (IDT) measurements by rapid compression machine (RCM) under engine-relevant conditions. The mechanism was then implemented in three-dimensional computational fluid dynamics (3D CFD) simulations to optimize combustion system design. Two ignition strategies were examined: direct in-cylinder and pre-chamber pilot diesel injection. Results show that optimal pilot diesel energy fractions are 3 % (97 % hydrogen) and 1 % (99 % hydrogen) for the in-cylinder and pre-chamber configurations, respectively. Under optimal conditions, the engine achieves 83 % of the power output of the prototype diesel engine and indicated thermal efficiency (ITE) of 49 %. Pre-chamber ignition improves lean mixture flammability, accelerates combustion, reduces sensitivity to pilot diesel variation, and mitigates high-temperature regions, offering a promising approach for enhancing efficiency and reducing NOx emissions in LTMHE.