Experimental examination of the effects of fuel octane and diluent on HCCI combustion

Homogenous Charge Compression Ignition (HCCI) combustion promotes higher thermodynamic efficiencies and lower oxides of nitrogen emissions in internal combustion engines, when compared to spark ignition and compression ignition combustion processes. Experiments on a single cylinder engine are conducted to examine the effect of fuel octane and mixture dilution on HCCI. Engine parameters, cylinder pressure and exhaust emissions are measured for three Octane Numbers (ON) while varying Exhaust Gas Recirculation (EGR) and air/fuel ratio. Results show that both the Start of Combustion (SOC) and burn duration are best influenced using dilution, rather than ON. However, the ON is effective in increasing the HCCI load range. A comparison of excess air and EGR dilution shows that EGR is a more effective at controlling the SOC and burn duration. HCCI combustion can result in a highly efficient engine with very low oxides of nitrogen emissions while using a low octane fuel.