Toshiaki Tanaka, Toyota Motor Corp. Power Train Engineering Div.2, Toshio Fujimura, Toyota Motor Corp. Engine Engineering Div.2, Souichi Matsushita, Toyota Motor Corp. Power Train Engineering Div.2, Akira Shoji, Toyota Motor Corp. Power Train Engineering Div.2, Seiji Okawara, Toyota Motor Corp. Material Engineering Div.1

 

1． Summary
Diesel engines with excellent fuel economy are receiving attention as an effective method of reducing CO2 emission to suppress global warming. However on the other hand, suppression of particularly particulate matter (hereinafter referred to as PM) and NOx emissions is the major issue from the aspect of improving urban environment.  To cope with this issue, we have developed a practical catalyst system (Diesel Particulate - NOx Reduction System: DPNR) that is a world first simultaneously reduction system of PM and NOx - a task that was previously considered impossible. This was accomplished by combining system control technology that realizes diesel engines to drive with a rich air-fuel ratio and catalyst technology (a NOx storage and reduction catalyst and a new highly porous filter substrate).

 

2．Technology
This system applies a DPNR catalyst, with a NOx storage and reduction catalyst uniformly coated on the wall surface and in the fine pores of a highly porous filter substrate, on a base comprised of a direct injection diesel engine with a newly-developed fuel injector installed on the upper stream of catalyst for adding fuel to the exhaust system, along with a common-rail fuel injection system capable of carrying out high-pressure, high-precision fuel injection control, plus a electrically controlled EGR system, in order to make it possible to drive with a rich air-fuel ratio, and to achieve precious catalyst temperature control (Fig. 1, Fig. 2).

Particulate matter emitted from the engine is temporarily caught in the fine pores of a highly porous filter substrate and then, starting at a low temperature of about 300?C, it is continuously by an active form of oxygen produced on the catalyst by repeated switching between a lean air-fuel ratio and rich air-fuel ratio and the oxygen contained in the exhaust gas. NOx is stored in the DPNR catalyst in the lean air-fuel ratio condition and is reduced in the rich air-fuel ratio condition. In this way , we have achieved the simultaneous reduction of particulate matter and NOx by this technology, which had previously been considered impossible in diesel engines (Fig. 3).
We applied this system to the diesel engine-powered light-duty trucks with a load capacity of 2 to 3 tons (Toyota Dyna, Hino Dutro) that are commonly used in urban logistics and started sales in Oct. 2003. Their figures for NOx emissions reached a 75% reduction level with respect to the Japan new short-term regulation implemented in Oct. 2003, and as to PM, they reached an 85% reduction level with respect to that regulation (in line with the new long-term regulation scheduled to take effect in October of 2005). Furthermore, in Europe, we applied this system to a passenger vehicle (Toyota Avensis) and after a large-scale field trials in Europe and Japan, started sales in Oct. 2003. This vehicle achieved a exhaust emission level much lower than that specified in the Euro 4 regulation, which will be implemented in 2005.

 

3．Conclusion
We demonstrated the possibility of realizing clean diesel vehicles with low CO2 emissions, by introducing in Japan and Europe with this system, which have extremely low emissions far below the regulation figures governing NOx and PM. In future, we hope to make wide application of this technology and contribute to improving the urban environment.