Numerical Analysis of Hydrogen combustion in Direct Injection Spark Ignition engine for Off-Road Applications

Hydrogen direct-injection spark-ignition (DI-SI) engines can deliver diesel-class power density, minute-scale refuelling and zero tail-pipe CO₂, an attractive combination for demanding off-road machinery, yet commercial roll-out is held back mainly by infrastructure cost, high fuel price and tank-system complexity rather than by in-cylinder science. Within that strategic context, this work tackles two complementary refinement issues, knock and cycle-to-cycle variability (CCV), whose control remains essential for a market-ready product. Cylinder-pressure-only analysis (CPOA) was performed at 1000 rpm, 200 N·m with λ = 1.8–2.3 and at 1800 rpm, 200 N·m with λ = 1.8–2.5. The low-speed point proved effectively knock-free and exposed CCV and inter-cylinder dispersion, whereas the high-speed point was clearly knock-limited. Knock severity was quantified with Maximum Amplitude of Pressure Oscillations (MAPO), Pressure Intensity (PI) and Integral Derivative (ID); MAPO and PI reproduced trends reported in the hydrogen-engine literature and mutually validated each other, while ID, though noisy on a single-cycle basis, converged on the same trend when 800 cycles were averaged. A start-of-injection sweep showed that neither very early nor very late injection offers a clear benefit; wall-heat losses dominate one extreme and mixture stratification the other, so a mid-range compromise is required. To explain these observations and enable predictive optimisation, Three-Pressure Analysis supplied burn-rate and turbulence data for two reduced-order models: a turbulence model tuned to the motored cycle and a combustion model configured to replicate the measured burn phases together with the experimentally observed knock and variability behaviour. The combined experimental and numerical framework clarifies why higher speed shortens end-gas induction time, why lean mixtures simultaneously suppress and destabilise hydrogen combustion, and why injection timing must balance mixture homogeneity against heat-release phasing, insights directly transferable to hydrogen DI engines intended for robust, knock-free operation in heavy-duty off-road applications.