Minaji Inayoshi

Achieving Lower Exhaust Emissions and Better Performance in an HSDI Diesel Engine with Multiple Injection

The effects of multiple-injection on exhaust emissions and performance in a small HSDI (High Speed Direct Injection) Diesel engine were examined. The causes for the improvement were investigated using both in-cylinder observation and three-dimensional numerical analysis methods. It is possible to increase the maximum torque, which is limited by the exhaust smoke number, while decreasing the combustion noise under low speed and full load conditions by advancing the timing of the pilot injection. Dividing this early-timed pilot injection into two with a small fuel amount is effective for further decreasing the noise while suppressing the increase in HC emission and fuel consumption. This is realized by the reduced amount of adhered fuel to the cylinder wall. At light loads, the amount of pilot injection fuel must be reduced, and the injection must be timed just prior to the main injection in order to suppress a possible increase in smoke and HC. After-injection, which injects a small amount of fuel immediately after the end of the main injection, reduces smoke, HC and fuel consumption. This is because the jet flame of the after-injection carries the remaining soot of the main injection to the squish area, and then oxidizes that together with the soot which previously existed in the squish area by promoted atmospheric temperature and enhanced mixing with fresh air.

Combustion Improvement for Reducing Exhaust Emissions in IDI Diesel Engine

Means for reducing PM from a swirl chamber type diesel engine were examined and the mechanisms of the PM reduction were investigated using both a multi-cylinder and an optically accessible single-cylinder engine. The following points were clarified. (1) At light load, suppression of initial injection rate reduces PM, because of both the change of ignition point to reduce SOF, and the retarded flowout of dense soot from the swirl chamber to reduce smoke. (2) Over medium load, the main cause of the exhaust smoke is hard spray-wall impingement which leads to both fuel adhesion on the wall and the stagnation of rich fuel-air mixture.