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The aim of this study is to develop a plasma-assisted after-treatment system for simultaneous reduction of NOx and PM in diesel exhaust, which is less sensitive to the fuel sulfur. The work presented focuses on development of a high-frequency dielectric barrier discharge reactor for oxidation of NO to NO2 in diesel exhaust and low-temperature oxidation of diesel soot with NO2. The first part of this paper describes the combustion characteristics of carbonaceous matters with pure NO2 and discusses the difference when oxygen is used as oxidation agent. The second part focuses on the development of a high-frequency dielectric barrier plasma reactor and describes the effects of plasma reactor configuration, energy density and gas composition on the NO conversion into NO2, and last part describes the soot oxidation with the plasma gas. The results reveal that NO can be efficiently oxidized into NO2 using the developed plasma reactor.

Effects of water-emulsified fuel on diesel combustion and emission reduction process were investigated under various ambient temperatures, equivalence ratios and water addition ratios using a rapid compression machine and a total-gas sampling device. The results indicate that promoted diffusion combustion of emulsified fuels offers a shorter combustion duration and an increase in amount of heat release when compared with those of gas oil. NOx concentration decreases with increasing the water content in emulsion fuels. This reduction is due to low NO formation rate and short duration of NO formation. Laser extinction measurement of the in-chamber KL factor shows that soot oxidation is promoted for emulsified fuels during the diffusion combustion stage.

This study investigates the effects of fuel properties on combustion characteristics and emissions such as NOx, smoke, THC and particulates in a direct-injection diesel engine. Fuel properties, such as cetane number and aromatic content, are varied independently in the experiments to separate their effects. The engine tests are carried out at steady operation with changed load, injection timing and injection pressure. The results show that reducing cetane number results in the increase of NOx and decrease of particulate emission at high load. This is because the low cetane number fuel has the long ignition delay and causes the high maximum heat release rate and the short combustion duration. However, high THC emission is produced at low load for the low cetane number fuel.

In this study it is tried to reduce NOx and particulate emissions simultaneously in a direct injection diesel engine based on the concept of two-stage combustion. At initial combustion stage, NOx emission is reduced with fuel rich combustion. At diffusion combustion stage, particulate emission is reduced with high turbulence combustion. The high squish combustion chamber with reduced throat diameter is used to realize two-stage combustion. This combustion chamber is designed to produce strong squish that causes high turbulence. When throat diameter of the high squish combustion chamber is reduced to some extent, simultaneous reduction of NOx and particulate emissions is achieved with less deterioration of fuel consumption at retarded injection timing. Further reduction of NOx emission is realized by reducing the cavity volume of the high squish combustion chamber. Analysis by endoscopic high speed photography and CFD calculation describes the experimental results.