Hydrogen Engine Insights: A Comprehensive Experimental Examination of Port Fuel Injection and Direct Injection

Abstract

The environmental and sustainable energy concerns in transport are being addressed through the decarbonisation path and the potential of hydrogen as a zero-carbon alternative fuel. Using hydrogen to replace fossil fuels in various internal combustion engines shows promise in enhancing efficiency and achieving carbon-neutral outcomes. This study presents an experimental investigation of hydrogen (H2) combustion and engine performance in a boosted spark ignition (SI) engine. The H2 engine incorporates both port fuel injection (PFI) and direct injection (DI) hydrogen fuel systems, capable of injecting hydrogen at pressures of up to 4000 kPa in the DI system and 1000 kPa in the PFI operations. This setup enables a direct comparison of the performance and emissions of the PFI and DI operations. The study involves varying the relative air-to-hydrogen ratio (λ) at different speeds to explore combustion and engine limits for categorising and optimising operational regions. Furthermore, load sweep tests are conducted at various engine speeds to evaluate the advantages of the H2 direct injection system over the PFI system and to analyse the characteristics of NOx emissions. Additionally, a matrix of inlet and exhaust valve timings is tested for each injection system to assess the valve timings and their interactions with injection setups on combustion, engine performance and emissions. The main findings of this study demonstrate that both PFI and DI hydrogen systems offer the benefit of zero carbon emissions and improved indicated thermal efficiency (ITE) when used in an engine designed and tuned for gasoline combustion. The DI hydrogen system, in particular, exhibits 2% higher ITE than PFI as well as producing higher power output. This enhancement can be attributed to the DI’s ability to operate under stoichiometric conditions, thanks to higher injection pressure and late injection timing during the intake stroke. This configuration mitigates backfire occurrences and prevents hydrogen from bypassing through the exhaust, thus enhancing combustion efficiency.