Hybrid Charging System for Heavy Duty Diesel Engines

In Japan, the next stage exhaust gas emission registration will be introduced around 1994. In case of heavy duty diesel engines, the level of NOx will be limited to 6.0g/kWh and the limit of particulate will be added to it. Its limit will be 0.7g/kWh. In U.S.A, regulation of particulate was already effective in 1988 and it will be tightened in 1991 and 1994. To pass these regulations, turbocharging with an intercooler is recommended to increase air flow, because reduction of black smoke at high load condition will be achieved by the improvement of combustion process. Also it will reduce negative effects by retard of injection timing that reduce NOx level. Although this improvement will be effective over approximate 1000rpm of engine speed, it will not be effective under 1000rpm because an engine can not get sufficient air flow due to poor performance of a turbocharger at this range. This is still one of unsolved problems at present. Systems to improve this defect are wastegate and variable geometry turbine. But wastegate system is suffered by poor fuel consumption at the high speed range of an engine. Variable geometry turbine system is also suffered by poor boost pressure at the very low engine speed. On the other hand, a supercharger, which is a positive displacement type compressor, can produce theoretically constant boost pressure throughout whole engine speed range because it is driven directly by a crank shaft and does not follow the flow characteristics of a turbine. It may be therefore possible to obtain a high performance system by combining these two boosting devices. That is “Hybrid system”. In this paper, the test results will be reported that obtained by applying this hybrid system to a diesel engine for trucks. Smoke level, specific fuel consumption, shaft torque and acceleration were improved.