Dynamic Transient Control of Hydrogen Direct-Injection SI Engines: Effects of Ramp Timing on Engine Performance and Abnormal Combustion

Dynamic Transient Control of Hydrogen Direct-Injection SI Engines: Effects of Ramp Timing on Engine Performance and Abnormal Combustion The application of hydrogen combustion engines in real-world transportation offers significant potential for high efficiency with zero carbon emissions. However, the adoption of zero-carbon hydrogen as the primary fuel across a wide operational range will require optimising transient performance to ensure efficient and safe operation, thereby eliminating abnormal combustion. This study investigates the transient control of a 0.4 Litre single-cylinder, downsized direct injection spark ignition (DI-SI) hydrogen engine, focusing on the impact of ramp timing on in-cylinder pressure overshoot, abnormal combustion behaviour, and overall engine performance. Utilising a closed-loop control strategy at a target lambda of 2.75, the research evaluates engine behaviour across a spectrum of transient intensities by varying the ramp timing from 1.38s to 0.24s. A detailed analysis reveals that as the ramp duration decreases, the sensitivity of the pressure rise rate increases significantly. This is primarily attributed to greater lambda variations resulting from the hydrogen-injection offset during lean-burn operation. Experimental results indicate that at the fastest ramp rate of 0.24s, the overshoot ratio of the in-cylinder pressure frequently exceeds mechanical safety limits. Furthermore, a direct correlation was identified between these rapid transients and an increased frequency of abnormal combustion cycles. The study exemplifies the need of maintaining ultra-low NOx emissions while highlighting the critical demand to balance response time with structural integrity. These findings suggest that transient calibration must prioritise the management of the overshooting ratio to ensure commercial viability.