Effects of Fuel Properties on Premixed Charge Compression Ignition Combustion in a Direct Injection Diesel Engine

Effects of fuel distillation characteristics and cetane number on premixed charge compression ignition (PCCI) combustion were investigated for the purpose of reducing NOx and PM emissions from a direct injection diesel engine. The test engine had a hole type injection nozzle for conventional diesel combustion at high load operation. A low compression ratio and cooled EGR were applied to the test engine in order to reduce the compression temperature for avoiding pre-ignition. The investigation results show that, in the case of ignition control by EGR, a light fuel with lower distillation characteristics had an advantage of reducing smoke at higher loads. This means that high volatility fuel is effective in promoting lean mixture formation of fuel and air during the ignition delay. Moreover, lowering the cetane number was effective in reducing NOx emissions by suppression of combustion temperature. But it was understood that an optimum cetane number exists, because excessive suppression of ignitability induced an increase in HC emissions and fuel consumption under a light load. From these results, it was found that PCCI combustion could be achieved up to middle load by using a fuel with low distillation temperatures and an optimum cetane number.