Water Injection Effects on a Heavy-Duty Hydrogen SI Engine

Hydrogen engines have gained interest recently, as they present a promising alternative for the decarbonization of heavy-duty transport, aligning with carbon neutrality regulations. This study investigates the effects of inlet manifold water injection on a heavy-duty hydrogen fueled spark ignition single cylinder engine, focusing on moderating abnormal hydrogen combustion and its impact on performance, thermal efficiency and exhaust emissions. Water injection has been identified as a potential solution to mitigate the challenges associated with hydrogen combustion, such as pre-ignition and knock, by reducing the reactivity of the mixture (reducing temperature and increasing the dilution). The lower reactivity of the mixture allows running richer lambdas without spontaneous preignition mitigating boosting requirements for full load and transient performance. Experimental results demonstrate that water injection significantly improves engine performance, thermal efficiency and exhaust emissions. By injecting water into the intake charge, the peak combustion temperature is lowered due to its cooling and dilution effect, leading to a reduction in nitrogen oxide (NOx) exhaust emissions. This also allows a better combustion phasing, because the pre-ignition tendency is reduced, enhancing thermal efficiency and performance. Furthermore, the study explores the possibility of increasing the compression ratio using water injection, to investigate the potential in thermal efficiency. The research highlights water injection effectiveness to control the hydrogen combustion, allowing the possibility to operate at higher loads, with more compression ratio and less boosting requirements. This paper shows the potential of water injection as a viable strategy to act as an enabler for highly efficient SI hydrogen engines capable of high load engine transient operations and low exhaust emissions, which is critical for heavy-duty applications under real-world conditions.