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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.

A new after-treatment system called DPNR (Diesel Particulate-NOx Reduction System) has been developed for simultaneous and continuous reduction of particulate matter (PM) and nitrogen oxides (NOx) in diesel exhaust gas. This system consists of both a new catalytic technology and a new diesel combustion technology which enables rich operating conditions in diesel engines. The catalytic converter for the DPNR has a newly developed porous ceramic structure coated with a NOx storage reduction catalyst. A fresh DPNR catalyst reduced more than 80 % of both PM and NOx. This paper describes the concept and performance of the system in detail. Especially, the details of the PM oxidation mechanism in DPNR are described.

Effects of fuel distillation characteristics and cetane number on premixed charge compression ignition (PCCI) combustion were investigated for the purpose of reducing NOx and PM emissions from a direct injection diesel engine. The test engine had a hole type injection nozzle for conventional diesel combustion at high load operation. A low compression ratio and cooled EGR were applied to the test engine in order to reduce the compression temperature for avoiding pre-ignition. The investigation results show that, in the case of ignition control by EGR, a light fuel with lower distillation characteristics had an advantage of reducing smoke at higher loads. This means that high volatility fuel is effective in promoting lean mixture formation of fuel and air during the ignition delay. Moreover, lowering the cetane number was effective in reducing NOx emissions by suppression of combustion temperature.

A new diesel after-treatment system, Diesel Particulate and NOx Reduction System (DPNR), is being developed for reducing PM and NOx emissions. We examined the effects of sulfur content in lubricants on exhaust NOx emission from DPNR catalyst, and examined the PM reduction ability using sulfur-free and aromatics-free fuel. After vehicle durability testing of 40,000 km without forced regeneration of PM and sulfur poisoning on DPNR catalyst, deterioration of DPNR was lower than using higher sulfur contents in fuel and oil. In addition to decreasing fuel sulfur, decreasing oil sulfur was also effective to maintain high NOx conversion efficiency. Although the catalyst was poisoned by sulfur in the lubricants, the influence of oil sulfur poisoning on the catalyst was lower than fuel sulfur poisoning. On the other hand, engine out PM emissions decreased by 70 % because of aromatics-free fuel. The pressure drop of DPNR did not increase during the 40,000 km vehicle durability test.

An analytical study has been carried out to investigate how the factors affecting ignition and formation of NOx and smoke can be influenced in indirect injection (IDI) diesel engines in order to increase engine output and reduce idling noise. It was found that controlling the heat release ratio between the swirl and main chambers was effective in reducing smoke and NOx emissions and in improving engine output. It vas also found that making the air jet flow counter to the fuel spray injected into the swirl chamber was effective in dispersing and atomizing fuel. This shortened the ignition delay period and reduced idling noise as a result. These factors have been incorporated into a newly developed dual-throat jet combustion system in which a sub-throat is provided in the swirl chamber, in line with the center axis of the fuel injection nozzle, in addition to the ordinary main throat.

The effects of gasoline fuel properties on exhaust emissions were investigated. Port injection LEVs, a ULEV, a prototype SULEV which were equipped with three–way (3–way) catalysts and also two vehicles with direct injection spark ignition (DISI) engines equipped with NOx storage reduction (NSR) catalysts were tested. Fuel sulfur showed a large effect on exhaust emissions in all the systems. In the case of the DISI engine with the NSR catalyst, NOx conversion efficiency and also regeneration from sulfur poisoning were dramatically improved by reducing sulfur from 30ppm to 8ppm. Distillation properties also affected the HC emissions significantly. The HC emissions increased in both the LEV and the ULEV with a driveability index (DI) higher than about 1150 (deg.F). The ULEV was more sensitive than the LEV. These results show that fuel properties will be important for future technologies required to meet stringent emission regulations.