Improvement of Engine Performance With Lean Mixture Ignited By Diesel Fuel Injection and Internal Egr

The uniform lean methanol-air mixture was provided to the diesel engine and was ignited by the direct diesel fuel injection. The internal EGR is added to this ignition method in order to activate the fuel in the mixture and to increase the mixture temperature. The test engine was a 4-stroke, single- cylinder direct-injection diesel engine. The cooling system was forced-air cooling and displacement volume was about 211 (cm³). The compression ratio was about 19.9:1.

The experiment was made under constant engine speed of 3000 (r/min). The boost pressure was maintained at 101.3 (kPa). Five values of mass flow rate of diesel fuel injection were selected from 0.060 (g/s) to 0.167 (g/s) and five levels of back pressure: 0), 26.7, 53.3, 80.0 and 106.6 (kPa) were selected for the experiment. The effect of internal EGR is varied by the back pressure level. It is confirmed that the lean methanol-air mixture of air-fuel ratio between 130 and 18 could be ignited and burned when the back pressure of 106.6 (kPa) is applied. The ignition delay reduces and the maximum combustion pressure increases as the back pressure increases. Fluctuation of maximum combustion pressure is gradually decreased as back pressure increases. However, the brake mean effective pressures decreases as the back pressure increases because the pumping loss and the reduction of the rate of specific heat cause the output power reduction. Therefore, the ignition and combustion characteristics can be improved by applying the internal EGR, however, the engine performance is deteriorated. When the back pressure of 106.6 (kPa) is applied, a lot of CO is emitted, and HC and NOx concentration decrease as back pressure increases. The stabilization of ignition and combustion caused by internal EGR makes HC concentration reduce.