Experimental Investigation of Homogeneous Charge Induced Ignition (HCII) with Low-Pressure Injection to Reduce PM Emissions in a Heavy-Duty Engine

Homogeneous Charge Induced Ignition (HCII) combustion utilizes a port injection of high-volatile fuel to form a homogeneous charge and a direct injection of high ignitable fuel near the Top Dead Center (TDC) to trigger combustion. Compared to Conventional Diesel Combustion (CDC) with high injection pressures, HCII has the potential to achieve diesel-like thermal efficiency with significant reductions in NOx and PM emissions with relatively low-pressure injections, which would benefit the engine cost saving remarkably. In the first part of current investigation, experiments were conducted at medium load with single diesel injection strategy. HCII exhibited great potential of using low injection pressures to achieve low soot emissions. But the engine load for HCII was limited by high heat release rate. Thus, in the second and third part, experiments were performed at high and low load with double diesel injection strategy. At high load, HCII with relatively low injection pressures (600-1000 bar) could obtain the same level of soot emissions as CDC with relatively high injection pressures (1200-1400 bar). The soot reduction could be over 50%. The particle number-size distribution analyses of PM emissions illustrated that the accumulation mode particulates were significantly reduced in HCII. Compared to CDC, indicated thermal efficiency for HCII was improved about 1-2% at high engine load. In addition, HCII could achieve Low Temperature Combustion (LTC) when combined with EGR, especially at low load. NOx emissions for HCII increased slightly at medium and high load, but decreased considerably at load low.