Partially Premixed Combustion of Gasoline Type Fuels Using Larger Size Nozzle and Higher Compression Ratio in a Diesel Engine

If fuels that are more resistant to auto-ignition are injected near TDC in compression ignition engines, they ignite much later than diesel fuel and combustion occurs when the fuel and air have had more chance to mix. This helps to reduce NO_X and smoke emissions at much lower injection pressures compared to a diesel fuel. However, PPCI (Partially Premixed Compression Ignition) operation also leads to higher CO and HC at low loads and higher heat release rates at high loads. These problems can be significantly alleviated by managing the mixing through injector design (e.g. nozzle size and centreline spray angle) and changing CR (Compression Ratio). This work describes results of running a single-cylinder diesel engine on fuel blends by using three different nozzle design (nozzle size: 0.13 mm and 0.17 mm, centreline spray angle: 153° and 120°) and two different CRs (15.9:1 and 18:1). The engine could be run on such blends with extremely low smoke and low NO_X at speeds and loads of up to 4000 rpm and 10 bar IMEP. The smoke at comparable NO_X levels was extremely high with diesel fuel at these conditions. The engine could also be run at near-idle conditions on these blends with levels of HC and CO emissions comparable with the diesel fuel. The wider volatility range with high compression ratio shows a benefit in avoiding over-mixing and over-leaning which could lead to poor combustion stability. The efficiency of PCCI combustion vehicle is expected to be about the same as for a diesel engine. PPCI combustion can be achieved more easily by using fuels with higher resistance to auto-ignition than conventional diesel fuel. Additionally, a successful commercial development of PCCI combustion vehicles could open the way for more efficient vehicles in markets where diesel fuel is not widely available for passenger car applications.