Environmental adaptability method for improving the cold start performance of the diesel engine based on pilot injection strategy

The deterioration of cold start performance at high altitudes is one of the main problems that restrict the altitude adaptability of diesel engines. In this study, by adapting the pilot injection strategy to improve cold start performance at different altitudes, the effect of the pilot injection ratio and pilot injection timing on the combustion, performance, and emission characteristics of diesel engines are investigated, and suggestions are proposed for optimizing fuel injection according to the altitude. The experimental results indicated that at high altitudes, the cold start performance was worse and more difficult to reach idle speed, NOx emissions increased due to the longer ignition delay. Compared to the single-injection strategy, the pilot injection strategy can effectively improve the combustion environment in the cylinder and thereby improve the cold start performance. As the altitude increase, decreasing the pilot injection mass can shorten the cold start time. The appropriate advance of pilot injection timing could improve mixture formation, which is conducive to improving the cold start performance and emissions at different altitudes. It can be concluded that advancing the pilot injection timing and increasing the pilot mass is a better injection strategy to improve cold start performance at plain. As the altitude increase, the pilot injection mass should decrease.