Influence of EGR and Pilot Injection on PCCI Combustion in a Single-Cylinder Diesel Engine 2011-01-1823

The effect of pilot injection and exhaust gas recirculation (EGR) on premixed charge compression ignition (PCCI) combustion was investigated in a single-cylinder direct-injection diesel engine with low engine speed and low load. The injection timing of PCCI combustion was fixed at 25 ~ 30 crank angle degree before top dead center (°CA BTDC) based on the ignition delay and power output. The level of oxides of nitrogen (NOx) emissions of PCCI combustion was 68% lower than that of conventional diesel combustion owing to the reduction of near-stoichiometric region which is well known as the main source of NOx formation. However, the indicated mean effective pressure (IMEP), hydrocarbon (HC), particulate matter (PM) and carbon monoxide (CO) emissions deteriorated compared with conventional diesel combustion because of early injection, advanced combustion phase and lowered combustion temperature.

EGR has been applied to PCCI combustion. As EGR rate increased, IMEP was increased due to the decrease of negative work during the compression stroke and NOx emissions was decreased because of dilution and thermal effects of EGR.

The pilot injection with a variation of split ratio and dwell time was also explored to enhance the mixing of fuel and fresh air. Certain conditions of pilot injection were effective for increase of IMEP and decrease of CO, HC and PM emissions because in-cylinder temperature was raised due to pilot injection, and this temperature rise enhanced the evaporation of the main injected fuel. The level of NOx emissions was higher than that of single injection because of raised in-cylinder temperature.

Consequently, the power output and emissions could be improved by applying pilot injection and EGR simultaneously in PCCI combustion.