Lean limit extension Aspects of gasoline direct injection (GDI) engine with hydrogen fraction

An experimental investigation was conducted on a spark-ignition gasoline direct injection (GDI) engine equipped with hydrogen port fuel injection (PFI) to investigate the effects of hydrogen enrichment on combustion characteristics, thermal efficiency, and exhaust emissions under lean-burn operation. Gasoline–hydrogen blends with different hydrogen mass fractions were tested at varying equivalence ratios, while spark timing was adjusted between 14° and 35° bTDC to compensate for hydrogen’s higher flame speed. The results showed that hydrogen addition accelerated combustion, shortened combustion duration, and significantly extended the lean operating limit. However, hydrogen enrichment generally increased nitrogen oxide (NOx) emissions because of higher in-cylinder combustion temperatures. Under homogeneous combustion conditions, hydrogen was supplied through port fuel injection (PFI) in the intake manifold with a start of injection (SOI) of 210° during the suction stroke, while the gasoline direct injection (GDI) SOI was set at 330° during the engine suction stroke. With a spark timing of 22° bTDC, 5.17% hydrogen by mass fraction reduced nitric oxide emissions by 0.29 g/kW-h and improved the hydrocarbon–NOx emission trade-off. Stable engine operation was achieved at an equivalence ratio of 0.55.