Effect of In Cylinder Water Injection Strategies on Performance and Emissions of a Hydrogen Fuelled Direct Injection Engine

The present work examines experimentally the effect of different direct water injection strategies on NOx emissions and performance in a direct injection hydrogen fueled engine. Three water injection strategies were considered including; injection at the suction, compression and expansion strokes. Both injection timing as well as quantity were varied for each strategy. The water injection configuration relative to the spark plug has been also evaluated. The results showed that water injection during expansion stroke has a minor effect on NOx emissions, which has been already formed. Noticeable effect could be achieved when water is injected at the later stages of the compression stroke. Reduction of NOx emissions is strongly dependent on the injection timing as well as quantity of the injected water. Optimum injection timing, for maximum NOx reduction, advances with the increase of the quantity of water being injected. Engine indicated thermal efficiency (ITE) also improves as water is injected during the later stages of the compression stroke. This is attributed to the optimization between the reduction in the compression work due to the inter-cooling effect while avoiding additional compression work due to the added mass. On the other hand, this is also due to the increase in the expansion work as a result of the added mass. The ITE improvement was dependent on water injection timing and injected amount. The range of water injection crank angles which ensure an improvement in the ITE was increased as the water amount increased.