Comparative analysis to assess the effects of hydrogen injection techniques on performance and emission characteristics of a compression-ignition engine

The need to decarbonise transportation has driven research into hydrogen as an alternative fuel for compression ignition engines. This study uses 1D combustion simulations to evaluate hydrogen injection strategies in a diesel engine with a 30 % hydrogen energy share (HES), including port fuel injection, gaseous direct injection (GDI), and blending liquid hydrogen with diesel. Performance metrics such as brake power, torque, brake thermal efficiency (BTE), brake specific fuel consumption (BSFC), brake mean effective pressure (BMEP), heat transfer rate (HTR) and emissions were analysed. Liquid fuels maintain power and torque, while port and direct injections reduce them by 10 % and 15 % due to uneven pressure rise and incomplete energy conversion. BTE remains stable with liquid fuels. However, it drops by up to 17.3 % and 15 % at 1500 rpm with port and direct injection but stabilises at higher speeds. Injection of liquid fuels has little effect on BMEP and HTR, while direct and port injections lower BMEP by 9.6 % and 14 % but increase HTR by over 70 % at high speeds. Port injection achieves the highest emissions reduction, cutting NOx by 54.4 % and CO by 99 %. Liquid fuels offer the best efficiency-performance trade-off, while port and direct injections prioritise emissions reduction at the cost of power. Furthermore, brake power and NOx emissions were evaluated across multiple engine loads (25 %, 50 %, 75 %, and 100 %) to capture load-dependent effects of hydrogen injection strategies.