Combined effects of diesel energy ratio and diesel injection nozzle diameter on natural gas high pressure direct injection engine with EGR

The natural gas (NG) high pressure direct injection (HPDI) engine has the advantages of low emission and high thermal efficiency, which is a promising engine type at present. In order to ensure the engine work performance and reduce the emission at the same time, this study analyzes in detail the effect of reducing the diesel injection nozzle diameter on combustion and emission with a reduced diesel energy ratio (DER). The results show that with a reduced DER, reducing the diesel injection nozzle diameter extends the time of diesel ignition for NG but reduces the range of diesel ignition. At different DER, reducing the diesel injection nozzle diameter deteriorates the mixing uniformity of NG and air. The mixing and ignition of NG both affect the combustion of NG. As the diesel injection nozzle diameter is reduced, the phases of peak heat release rate (HRR) and peak cylinder pressure advance. The peak of HRR decreases and the maximum cylinder pressure increases. NOx and HC emissions decrease, but soot emission increases. The Indicated thermal efficiency (ITE) of the engine is maintained at 45% regardless of changing the diesel injection nozzle diameter or DER within the range studied in this paper.