Abstract The present study focuses on the experimental investigation on the optimal pilot injection strategy under GCI combustion mode in a multi-cylinder heavy-duty diesel engine. Three experiments were conducted at a high-speed high-load operating point with different operating parameters and emission targets, namely engine-out NOx target, fuel injection pressure, and main injection timing. The engine-out NOx targets were set to 5.0 g/kWh and 1.5 g/kWh, and the gasoline injection pressures were set to 100 MPa and 140 MPa. These high and low values represent different requirements of SCR efficiency and practical capability of fuel supply system when addressing the hypothetical future tailpipe NOx limit of 0.02 g/hp-hr (0.027 g/kWh). The results show that the use of optimized pilot injection always achieves lower pressure rise rate and soot emissions than the single injection baseline. The pilot gasoline fuel with low injection pressure is more ignitable than that with high injection pressures, hence a distinct heat release spike usually occurs for a pilot injection. The optimal pilot mass should be increased for a higher fuel injection pressure because the pilot fuel stratification level decreases. A relatively late pilot timing is preferable for the early main injection timing. For the late main injection timing, however, a relatively early pilot timing with large pilot mass is preferable and brings about a distinct two stage high temperature heat release, which can reduce the fuel consumption and soot emissions simultaneously. The two stage split combustion process obtained by double injection with retard combustion phasing can be considered to be an important way to alleviate the requirement of GCI fuel system.

中文翻译：

---

多缸柴油机汽油压燃（GCI）燃烧的先导喷射策略管理

摘要 本研究的重点是多缸重型柴油机GCI燃烧模式下优化预喷射策略的实验研究。在高速高负荷工况下进行了三个实验，分别具有不同的运行参数和排放目标，即发动机输出 NOx 目标、燃料喷射压力和主喷射正时。发动机输出的 NOx 目标设定为 5.0 g/kWh 和 1.5 g/kWh，汽油喷射压力设定为 100 MPa 和 140 MPa。这些高值和低值代表了在解决假设的未来尾管 NOx 限值 0.02 g/hp-hr (0.027 g/kWh) 时对 SCR 效率和燃料供应系统实际能力的不同要求。结果表明，与单次喷射基线相比，使用优化的先导喷射总是能实现更低的压力上升率和碳烟排放。低喷射压力的引燃汽油比高喷射压力的燃油更易点燃，因此引燃通常会出现明显的放热尖峰。由于引燃燃料分层水平降低，因此对于更高的燃料喷射压力应该增加最佳引燃质量。对于较早的主喷射正时，优选相对较晚的先导正时。然而，对于较晚的主喷射正时，较早的先导质量较大的先导正时是优选的，并且带来明显的两阶段高温放热，这可以同时降低燃料消耗和烟尘排放。