Abstract
In a series of studies, we have proposed a combustion concept aimed at significantly reducing NOx emissions by stratifying water within the engine cylinder. In the first report, under conditions with an indicated mean effective pressure (IMEP) of 0.8 MPa, we demonstrated that when water injection was employed, NOx decreased to 1/4 level under equivalent soot concentration conditions compared to cases without water injection. In this second report, we evaluated engine performance under higher load conditions with an IMEP of 1.2 MPa. Utilizing 3D-CFD analysis, we found that stratifying water at the upper part of the piston cavity results in a 10-point higher reduction in NOx compared to homogeneously distributing water within the cylinder. While Exhaust Gas Recirculation (EGR) strategies pose challenges due to increased soot levels, our NOx reduction strategy using water injection showed a lesser increase in soot, leading to a higher reduction in NOx under equivalent soot concentration conditions. Subsequently, experiments were conducted using a multi-hole fan spray nozzle to achieve the layered distribution of water. The results demonstrated that, under conditions where the water injection quantity was 50% of the fuel amount, the optimization of timings and interval for split water injection led to approximately a 40% reduction in NOx under conditions of equivalent soot concentration. Furthermore, the impact on the heat release rate due to water injection was minimal, and the decrease in heat losses resulted in only a marginal decline of about 0.4 points in indicated thermal efficiency.
