Transient optimization of intake system control of a DI hydrogen engine with a novel evaluation of transient and steady state performance

Enhancing transient performance in hydrogen engines remains a significant challenge due to the high air flow requirements associated with lean-burn operation. In this study, fixed-speed transient tests from 2 to 12 bar BMEP are performed at 2500 and 4500 rpm on a 2.0 L direct-injection hydrogen engine. The torque response at 2500 rpm is comparable to that of conventional gasoline engines, however, transient NOx emissions remained unacceptably high. Different strategies are generated with reducing wastegate (WG) opening and changing variable valve timing (VVT) in the base calibration, and their effects on transient performance are systematically evaluated. Reducing the WG opening, proves effective in rapidly increasing the transient λ, resulting in NOx reduction of 35.8% at 4500 rpm, while delivering a more substantial 71.6% reduction at 2500 rpm where turbocharging is insufficient. Transient VVT adjustment is further implemented to prioritize low NOx emissions over maximum thermal efficiency. By effectively increasing the transient minimum excess air ratio (λmin), this strategy achieved an additional reduction in transient NOx emissions of up to 73.8%, at the cost of only a 1.6% increase in fuel consumption at 4500 rpm. In addition, a comparison of different turbocharger configurations demonstrates turbocharger matching has a pronounced influence on the transient performance of hydrogen engines. Finally, several indicators are introduced to characterize turbocharger response and operational stability, and a novel comprehensive assessment method is established to evaluate both transient and steady-state hydrogen engine performance using the coefficient of variation method under different application scenarios.