Nitrogen Oxides Reduction Potential Via Water Direct Injection in a Single-Cylinder Hydrogen-Fueled Direct Injection Spark Ignition Engine

In hydrogen-fueled internal combustion engine (H₂ICE), there are some ways to reduce nitrogen oxides (NOx) emissions. Using the wide flammability range of hydrogen, such as conducting lean combustion to reduce nitrogen oxides and employing exhaust gas recirculation (EGR), have been adopted. However, challenges exist in terms of load expansion, and due to the absence of high heat capacity of carbon dioxides in the exhaust, EGR also struggles to exhibit significant effects. In such a scenario, there is growing interest in injecting water into the H₂ICE as an alternative to augment the EGR effect. In this study, the spark ignition (SI) single-cylinder engine equipped with two direct injectors was used to evaluate the hydrogen and the water dual direct injection combustion system. This system involved the direct injection of hydrogen using a wall-guided gasoline direct injector and the direct injection of water into the combustion chamber using a diesel injector. This approach utilizes the vaporized water not only to act as EGR but also to aid in combustion chamber cooling through the latent heat of vaporization of water, thereby reducing the impact on volumetric efficiency. The main variables were injection timing and the amount of water. Engine speed was fixed at 1,500 rpm and there were two excess air ratio conditions at 2.2 and 1.5(richest limit condition). The result emphasized that the maximum NOx reduction potential was 80% when the water amount was 15.8 mg/str under the excess air ratio of 2.2 due to its latent heat and dilution effects. In addition, this value correspondence to EGR 27.4% so that water direct injection was effective to reduce NOx emissions.