Experimental study on the effect of micro-addition of hydrogen on diesel ignition and combustion characteristics in an external heating constant volume combustion chamber

In light of the urgent need to reduce greenhouse gas emissions, hydrogen has emerged as a promising alternative fuel for compression ignition engines. Considering the challenges of onboard hydrogen storage and transportation, micro hydrogen addition in marine diesel engines is a viable transitional fuel strategy. This study employs an externally heated constant volume combustion chamber (CVCC) to experimentally investigate hydrogen-diesel combustion under simulated top dead center (TDC) conditions. High-speed photography was utilized to capture the ignition and combustion processes across six injection strategies, systematically varying three key parameters: hydrogen fraction (1.5%–3% vol.), injection pressure (60–120 MPa), and fuel mass (11.27–21.51 mg). The results show that higher injection pressures advance ignition timing (IT) by improving atomization, but excessive pressure (120 MPa) causes spray-wall impingement, reducing combustion efficiency and soot production. Hydrogen addition exhibits a non-linear effect on IT – 1.5% H 2 delays ignition due to oxygen displacement, while 3% H 2 advances IT because hydrogen’s lower heat capacity enhances local temperatures. The 90 MPa condition demonstrates the largest flame area and highest heat release rate (HRR), indicating optimal combustion performance. Increased injection mass prolongs ignition delay and suppresses flame luminosity due to deteriorated air-fuel mixture quality. Hydrogen addition shows a linear influence on combustion intensity, with higher concentrations leading to stronger combustion intensity.