Effects of scavenging port angle and combustion chamber geometry on combustion and emmission of a high-pressure direct-injection natural gas marine engine

Abstract

ABSTRACT HPDI natural gas (HPDI-NA) engines can improve nitrogen oxides and PM emissions while getting better in-cylinder combustion in the comparison of the conventional engines fueled with diesel. In this paper, a three-dimensional (3D) of a HPDI natural gas marine engine is set up. The influence of geometry parameters on mixture flow, combustion, and emissions were presented and discussed. The geometry parameters include scavenging port angle (SPA) and three combustion chamber geometries (shallow-basin-shaped (SBC), shallow-ω-shaped (SWC), and deep-pit-shaped combustion chamber (DPC)). The results show that increasing the SPA can significantly swell the swirl ratio, but too large the swirl ratio is not conducive to improving the scavenging effect. As SPA is varied from 30° to 60°, a richer-than-flammable region gets greater, and the penetration distance is shortened by the larger vortex. Then, the mixing and combustion process get worse. With the increase of the SPA, the emissions of soot, carbonic oxide (CO), and unburned hydrocarbons (HC) can be optimized. Also, a larger scavenge port angle is not conducive to improving nitrogen oxides emission and the fuel consumption efficiency. The combustion chamber geometries have fewer effects on the mixture flow and the pressure profiles and temperature than that of SPA. The CO/HC and soot emissions of the three tested combustion chamber geometries are similar. The effect of the shallow basin-shaped combustion chamber (SBC) is much better than that of the other combustion chamber geometries with respect to NOx emission.