Numerical investigation of the effect of altitude on diesel engine combustion and soot emissions

It is increasing concerned that the plateau environment will potentially increase fuel consumption in engines. Despite this, the current state of research on high altitude engines is still inadequate in providing sufficient and detailed information to counteract the decrease in engine efficiency. In addition, one of the novelty of this study was that the investigated altitudes is up to 4500 m, of which the previous studies was limited. Therefore, this study aims to investigate the effect of altitude on in-cylinder spray, combustion, and soot formation processes in diesel engines. A calibrated three-dimensional (3D) computational fluid dynamics (CFD) model of a single-cylinder, four-strokes, direct injection (DI) compression ignition, intake boost research diesel engine is established. The numerical CFD model used in this study has been validated through comparison with experimental data. It effectively investigates the in-cylinder activities and provides insights into the causes behind combustion and soot emission deterioration. The simulation is operated at altitudes of 0, 1500, 3000, 4500 m with corresponding intake pressure. It has been observed that engine performance and soot emissions deteriorate as altitude increases, and a sharp drop occurs when the altitude exceeds 3000 m, which can be attributed to the dramatic decline in combustion efficiency. The extended spray leads to a decrease in air utilization, which ultimately results in a sudden drop in combustion efficiency at altitudes above 3000 m. Overall, this study has identified that the extended penetration of the spray, caused by reduced pressure and air density, leads to poor air utilization, resulting in decreased performance and increased emissions. Hence, it is recommended that optimization of the combustion chamber geometry and injection strategies of diesel engines operating at high altitudes be undertaken to improve air utilization and combustion quality. This will serve as an avenue for further research in the future.