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As a research of low temperature regeneration of DPF, combustion mechanism of diesel particulate matter (PM) trapped in DPF was investigated. For the assumption of PM combustion mechanism, the relationship between PM combustion characteristics and the physical properties of PM particles was investigated by using thermal and spectroscopic analysis methods. Experimental PM samples were produced under typical engine operating conditions using three representative fuels, two commercial diesel fuels containing aromatics (JIS-2 and Class 1) and a paraffin fuel that was prepared in a gas-to-liquid (GTL) process and did not contain any aromatics. Based upon these characteristics and combustion test results of the PM samples, a mechanism of the PM combustion was assumed. And the crystallinity of PM particles and existence of some surface functional groups containing oxygen are thought to be the important factors to lower the temperature of PM combustion., independent of the fuel type.

Experimental investigations were previously conducted with a direct-injection diesel engine with the aim of reducing exhaust emissions, especially nitrogen oxides (NOx) and particulate matter (PM). As a result of that work, a combustion concept, called Modulated Kinetics (MK) combustion, was developed that reduces NOx and smoke simultaneously through low-temperature combustion and premixed combustion to achieve a cleaner diesel engine. In subsequent work, it was found that applying a low compression ratio was effective in expanding the MK combustion region on the high-load side. The MK concept was then combined with an exhaust after-treatment system and applied to a test vehicle. The results indicated the attainment of ULEV emission levels, albeit in laboratory evaluations. In the present work, the combination of the MK combustion concept and certain fuel properties has been experimentally investigated with the aim of reducing exhaust emissions further.

A new auto-ignition combustion model for performing multi-zone engine cycle simulations has been developed to investigate the characteristics of compression ignition combustion in gasoline engines. In this combustion model, the auto-ignition timing is predicted with a modified shell model and combustion speed is calculated with a three-region (burned, ignited and unburned) model. Engine cycle simulations performed with this model were used to analyze the effect of engine operating parameters, i.e., temperature and air-fuel distributions in the cylinder, on combustion characteristics. It was found that the air-fuel distribution in the cylinder has a large impact on combustion characteristics and knocking was prevented by creating a fuel-rich zone at the center of the cylinder under high load conditions. The fuel-rich zone works as an ignition source to ignite the surrounding fuel-lean zone. In this way, two-step combustion is accomplished through two separate auto-ignitions.

There have been strong demands recently for reductions in the fuel consumption and exhaust emissions of diesel engines from the standpoints of conserving energy and curbing global warming. A great deal of research is being done on new emission control technologies using direct-injection (DI) diesel engines that provide high thermal efficiency. This work includes dramatic improvements in the combustion process. The authors have developed a new combustion concept called Modulated Kinetics (MK), which reduces smoke and NOx levels simultaneously by reconciling low-temperature combustion with pre-mixed combustion [1, 2]. At present, research is under way on the second generation of MK combustion with the aim of improving emission performance further and achieving higher thermal efficiency [3]. Reducing heat rejection in the combustion chamber is effective in improving the thermal efficiency of DI diesel engines as well as that of MK combustion.

Nitrogen oxide (NOx) and particulate matter (PM) emissions of diesel vehicles are regarded as a source of air pollution, and there is a global trend to enforce more stringent regulations on these exhaust gas constituents in the early years of the 21st century. On the other hand, the excellent thermal efficiency of diesel engines is certainly a welcome attribute from the standpoints of conserving energy and curbing global warming. Recently, many research institutes around the world have been using high-efficiency direct-injection (DI) diesel engines to research emission control technologies. The authors have also been engaged in such research [1,2]. As a result of this work, we have developed a new combustion concept, called Modulated Kinetics (MK), that reduces NOx and smoke simultaneously due to low-temperature and premixed combustion characteristics, respectively, without increasing fuel consumption [3,4].