Enhancing hydrogen internal combustion engine efficiency through improvement of injection timing and mixture homogenization dynamics

Abstract

Hydrogen is increasingly investigated as a fuel for internal combustion engines (ICEs) to reduce carbon emissions. However, its low density and large volume during compression pose challenges for mixture homogenization, which is critical for achieving high thermal efficiency and ultra-low NOx emissions. This study examines the influence of piston geometry on mixture formation in hydrogen-fueled ICEs. One dimensional and three dimensional coupled simulations were conducted for different piston designs under part-load and full-load conditions, with a predefined homogeneity index (HI) used to evaluate mixture quality. Results show that with the proposed m-lens piston, hydrogen injection can be retarded by 30 degrees CA at 1000 rpm part load and 20 degrees CA at 1600 rpm full load while maintaining the same HI similar to 80 % and similar to 60 % for part load and full load respectively as the base piston, leading to a 2.74 % improvement in brake thermal efficiency (BTE) for part load and %1.18 % BTE improvement for full load. Computer Fluid Dynamics (CFD) analysis further revealed that m-lens pistons produce a more fragmented mixture and a dominant single vortex with lower spatial flow complexity, while reentrant pistons yield more centralized mixtures with multiple interacting swirl centers, suggesting multidirectional turbulence. Internal energy (IE) distributions were similar under part load but more fragmented under full load, also average IE and standard deviation of IE is slightly lower for m-lens piston, additional to this re-entrant pistons exhibited higher energy peaks near the exhaust valve region, of indicating an increased preignition tendency.