Investigation of transient emission control strategies for a turbocharged direct-injection hydrogen engine

Abstract

Hydrogen internal combustion engines (H 2 ICEs) have been demonstrated to achieve high efficiency and near-zero NO x emissions under stable lean-burn operation. However, the low exhaust enthalpy slows turbocharger response, while rapid load increases can cause λ deterioration and intensify NO x formation. Therefore, transient NO x emission peaks remain a key challenge for H 2 ICEs. This study experimentally investigates transient NO x control strategies for a 2.0 L turbocharged DI H 2 ICE during 2–12 bar BMEP ramps at 2500 and 4500 rpm. For the severe 3 s ramp, wastegate pre-closure and load-dependent variable valve timing regulation were first applied to enhance transient air-path response, substantially reducing NO x emissions. Based on this regulation, transition scheduling was then optimized by varying the transition point (TP) and the pre-/post-TP time allocation to further reshape the BSFC–BSNO x trade-off. The entropy weight method combined with TOPSIS was used to identify the optimum strategy. The selected strategies were TP30% with a 0.5 + 2.5 s allocation at 2500 rpm and TP50% with a 1.0 + 2.0 s allocation at 4500 rpm. Compared with the Baseline strategy, the final combined strategies reduced BSNO x from 12.99 to 1.40 g/kWh at 2500 rpm and from above 22.22 to 2.19 g/kWh at 4500 rpm. Meanwhile, BSFC slightly decreased from 83.85 to 83.18 g/kWh and from 88.90 to 88.83 g/kWh, while turbocharger speed-rise attainment increased from 69.58% to 79.37% and from 78.47% to 90.42%, respectively. These results provide a practical approach for reducing transient NO x emissions in automotive turbocharged DI H 2 ICEs without additional boosting hardware.