Dynamic transient control of hydrogen direct-injection SI engines: effects of ramp duration on engine performance and abnormal combustion

Hydrogen internal combustion engines offer a route to near-zero carbon on-road transport while preserving existing engine manufacturing and calibration know-how. Translating that potential into real-world driving, however, depends on transient control; steady-state maps alone cannot guarantee either safe operation or low NOx emissions during load steps. This paper reports a controlled transient sweep on a 0.4 L single-cylinder direct-injection spark-ignition hydrogen research engine. Five ramp durations (1.38, 1.08, 0.84, 0.48 and 0.24 s) were evaluated at a constant engine speed of 2,000 rpm with a target relative air–fuel ratio of 2.75 under closed-loop feedback control. The measurements track injection pulse width, spark timing, boost, lambda, IMEP, peak in-cylinder pressure and the maximum pressure rise rate ( R max ) through each transient. As ramp duration is shortened, lambda excursions and air-path overshoot grow rapidly: at 0.24 s the in-cylinder pressure overshoot approaches the mechanical safety limit, IMEP overshoots the steady-state target by about 22 %, and R max exceeds the 600 kPa/°CA calibrated threshold. With a ramp of 0.48 the most hazardous R max peak at roughly 1,000 kPa/°CA is caused, demonstrating that fastest is not always most damaging. Only the 1.38 s baseline keeps all combustion-severity metrics inside their reliability envelope. A feed-forward fuelling term scaled by the rate of manifold pressure change dP / d t is proposed to close the transient lambda gap; with physical implementation and experimental validation proposed as a future optimisation step. The results identify pressure-gradient management as the binding constraint for transient calibration of lean DI hydrogen engines.