Synergistic effects of gas-to-liquid pilot ignition and high rates of nitrogen-based simulated EGR on PREMIER combustion in dual-fuel hydrogen engines

Hydrogen-fueled compression-ignition engines offer a pathway to decarbonize heavy-duty propulsion but face a trade-off between thermal efficiency, NOx emissions, and narrow knock-free windows. Although EGR dilution and pilot-fuel reactivity control have each been studied independently, their combined effect on hydrogen PREMIER (PREmixed Mixture Ignition in the End-gas Region) combustion has not been systematically characterized. This study addresses that gap by comparing diesel and high-cetane Gas-to-Liquid (GTL) pilot fuels in a supercharged hydrogen dual-fuel engine, while varying nitrogen addition to isolate the inert dilution effect of simulated EGR (0–50%). GTL's superior ignitability shortened ignition delay and enhanced combustion stability versus diesel. Increasing inert EGR (nitrogen) dilution suppressed NOx by over 90% (360 to 30 ppm) via reduced peak temperatures, while sustaining knock-free PREMIER combustion and achieving a peak indicated thermal efficiency of 43.55% at ∼0.80 MPa IMEP. Coupling pilot-fuel reactivity control with EGR dilution enables safe, clean, high-efficiency hydrogen dual-fuel.