We have realized ultra low exhaust emission that meets U-LEV standards in Japan by applying a simultaneous reduction system of NOx and particulate matter (hereinafter referred to as PM) to the diesel engine for light-duty trucks. This system has been introduced to the Japanese market since September 2003.
The basic technologies comprise Diesel Particulate-NOx Reduction system (DPNR), common rail injection system necessary for accurately controlling the catalyst bed temperature and the air to fuel ratio, electrically controlled EGR system, high-efficiency EGR cooler, and the fuel injector installed on the upper stream of catalyst that feeds over-rich fuel-air mixture for NOx reduction with DPNR catalyst and SOx discharging.
To realize simultaneous reduction of NOx and PM with DPNR, the important issues include the clogging of PM to the filters after continuous driving at low vehicle speed and the sulfur poisoning of the catalyst. In the current development, we have constructed system control measures and verified that it is possible to make forced PM oxidation and SOx discharging under various conditions simulating real world driving.
Another important issue to clear in applying the after-treated system to the light-duty trucks is to retain catalytic durability. In the current development, durability tests were conducted for an extended period of time using 40ppm and 7ppm sulfur fuels. As a result, we have successfully met the U-LEV (75% reduced level from the new short-term regulation) in Japan and the standard value 85% reduced from the new short-term regulation for PM by using 7ppm sulfur fuel.
In order to accomplish further reduction of exhaust emissions in the future for the benefit of a better environment, the availability of ultra-low sulfur fuel is essential.