Search Results

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.

Fischer-Tropsch Diesel (FTD) fuel is expected to be a promising clean diesel fuel in the future because of its characteristics of zero sulfur, zero aromatics and a high cetane number. However, the optimum fuel properties for diesel engines have not been realized. In this study, the effects of cetane number and distillation characteristics on engine-out PM emissions from a conventional direct injection diesel engine were investigated by using paraffinic fuels which were made to simulate FTD fuel. From the results of the vehicle exhaust emissions test and engine dynamometer test, it was found that the narrow distillation characteristics (which eliminates heavy hydrocarbon fraction) could reduce the soluble organic fraction (SOF) in PM emissions, and the excess high cetane number characteristic promoted the formation of insoluble organic fraction (ISOF).

The white smoke generated by a diesel engine was analyzed and found to consist mainly of hydrocarbons. Test results indicated that the emission level depends on ambient temperature. A compact white smoke meter was developed to enable emission levels to be accurately measured. The internal temperature of this meter is controlled so that white smoke is generated within the measuring device. The meter was used to evaluate the effectiveness of various white smoke emission control devices for the DI diesel engine. The results indicated that an intake air heater offers the greatest potential. Accordingly, a new intake air heater with ceramic PTC thermistor having a very high heating efficiency was developed to reduce white smoke emission.

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.

Influence of sulfur poisoning on NOx storage - reduction catalysts (NSR catalysts) was examined using both model gas and an actual vehicle. Deterioration of NSR catalysts is explained as the balance of sulfate formation in lean operating conditions and the amount of sulfate decomposed under rich operating conditions. This study focused on sulfate decomposition characteristics of NSR catalysts. First, sulfate decomposition characteristics of an NSR catalyst were examined in a model gas test. It was found that the initial temperature of SOx release was higher than the sulfur poisoning temperature. Crystal growth of sulfate by increasing temperature was assumed, and hence suppressed SOx release. Second, various sulfur concentrations (8 - 500 ppm) in gasoline were used for vehicle durability. The duration of one durability cycle was 1,260 seconds, including a 60 second regeneration of sulfur poisoning (AFR 14.2, 700 °C).