Effect of injection pressure on the impinging spray and ignition characteristics of the heavy-duty diesel engine under low-temperature conditions

In the heavy-duty diesel engine, the unavoidable impinging spray and ignition during low-temperature ignition have a significant impact on engine performance. In this study, the effects of injection pressure on the impinging spray and ignition characteristics of the heavy-duty diesel engine with a 0.32 mm nozzle were measured visually in a constant volume combustion chamber using Mie-scattering, shadowgraph, and direct photography methods. The results show that at 550 K and 750 K, as the injection pressure increases, the radius, height and area of liquid/vapor impinging spray increase due to the increase in momentum. However, the above parameters show an opposite trend during the post-stage of impinging spray due to the enhanced evaporation at 850 K. In addition, higher injection pressure shortens the lifetime of liquid fuel adhesion, resulting in an increase in the ratio of vapor to the total liquid/vapor spray area. For impinging ignition, the flame rapidly propagates from periphery to the center, but the impinging-point region still misfires due to the mixture that is too rich or too cool. Furthermore, the increased injection pressure shortens the ignition delay especially for larger fuel mass but also reduces the spatially integrated natural luminosity and flame area, that is, more unburned fuel due to excessive evaporation and heat absorption. Therefore, for the heavy-duty diesel engine, it is optimal to appropriately increase the injection pressure to ensure rapid start-up while reducing misfire or incomplete combustion at low temperatures.