Toward ultra-low emissions combustion in a dual fuel diesel-hydrogen engine under low load condition: a 3D-CFD study

Decarbonising Compression Ignition (CI) engines remains critical in marine, heavy-duty and off-road sectors with long asset lifetimes favouring retrofit solutions. Hydrogen can displace Diesel, yet ultra-high Hydrogen Energy Share (HES) is limited by rapid heat release, NO x formation and excessive pressure rise. This study employs a 3D-CFD model, calibrated against nine experimental operating points, to numerically explore ultra-high HES in a dual fuel Diesel–hydrogen engine at low load (1200 rpm, IMEP = 6 bar). A single-pilot Reactivity Controlled Compression Ignition (RCCI) strategy, with advanced Diesel injection promoting distributed ignition of an ultra-lean H 2 –air mixture, extends hydrogen utilization without violating mechanical or emissions constraints. Two configurations emerge: HES = 96% (SOI = 660°CA) delivers +4.4% gross indicated efficiency, −88.6% CO 2 and −98% NO x ; HES = 98% (SOI = 655°CA) achieves −94% CO 2 and −99.7% NO x . In both cases the peak in-cylinder pressure and the Peak Pressure Rise Rate stay within the structural design limits of the single-cylinder research engine used in this study (180 bar and 20 bar/°CA respectively).