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We already found that PM layer deposited on the cooled wall in an EGR cooler was separated from the wall under cold start condition. In this study, effects of cooled wall temperature and hydrocarbon (HC) concentration in exhaust gas on the separation behavior of PM deposit layer in a test EGR cooler were investigated experimentally. As a result, it was found that the PM layers which were deposited with high wall temperature was hard to separate from the wall compared with the layers deposited with low wall temperature during the cold start test. As for the HC concentration in exhaust gas, PM layer deposited in higher HC concentration, which was achieved by addition of diesel fuel to the test exhaust gas, was easily separated during the cold start test.

Among the emerging technologies in order to meet ever stringent emission and fuel consumption regulations, Exhaust Gas Recirculation (EGR) system is becoming one of the prerequisites particularly for diesel engines. Although EGR cooler is considered to be an effective measure for further performance enhancement, exhaust gas soot deposition may cause degradation of the cooling. To address this issue, the authors studied the visualization of the soot deposition and removal phenomena to understand its behavior. Based on thermophoresis theory, which indicates that the effect of thermophoresis depends on the temperature difference between the gas and the wall surface exposed to the gas, a visualization method using a heated glass window was developed. By using glass with the transparent conductive oxide: tin-doped indium oxide, temperature of the heated glass surface is raised.

In this study, formation behaviors of soot in laminar diffusion flames of diesel fuel with fatty acid or fatty acid methyl ester (FAME) were investigated. Oleic acid and oleic acid methyl ester were selected as fatty acid and fatty acid methyl ester. Combustion gas emitted from the laminar diffusion flame was sampled, and PM composition in the gas was analyzed. Laser induced incandescence (LII) and laser induced fluorescence (LIF) techniques were applied to measure soot and polycyclic aromatic hydrocarbon (PAH) distributions in the laminar diffusion flames. As the results, soot emission and soot incandescence distributions were decreased by the addition of fatty acid or fatty acid methyl ester. Moreover, PAH concentration in the closed flame became high by addition of fatty acid or fatty acid methyl ester.

Recently, for reduction of PM emission from diesel engine, low sulfur diesel fuel was introduced and commercialized. There are some reports for effect of fuel sulfur on PM characteristics by using engine dynamometer tests. However, it is difficult to understand mechanism of PM formation and effect of fuel sulfur on PM formation process. Thus, investigation by a simple flame is effective way for understanding detail PM formation process. In this paper, effect of sulfur content in fuel on PM characteristics was investigated by using laboratory-scale PM generator. Test fuels were diesel and surrogate diesel fuel, and sulfur concentration in the surrogate fuel was controlled with thiophene addition. Effects of fuel sulfur on PM were clarified with characteristics of PM obtained from PM number distribution measurements and PM compositions analysis.

In this study, using a droplet dripping and evaporation test rig, over ten thousands droplets of diesel and bio-diesel fuels were dripped on a hot surface repeatedly, and evaporation deposits formed from them were quantitatively analyzed. Results show that wet-dry condition and hot surface temperature were main controlling factors of deposits development. Empirical equations of deposits development were derived from the experimental results. Further carbonaceous evaporation deposits from RME were around ten times serious than diesel fuel. The main reason of it was that bio-diesel fuel was produced from various plant oils through esterification and it was liquid phase chemical reaction process with no hot distillation, so that thermal stability of bio-diesel fuel was poor.

In this study, compositions, size distributions and activation energy in oxidation of diesel PM were investigated. Benzene (C6H6) was mixed to diesel fuel as a promoter of PM formation, and further, ferrocene (Fe(C5H5)2) was added as a promoter for oxidation processes during in-cylinder combustion and after-treatment. The effect of those additions on the PM characteristics was discussed on the basis of measured results such as SOF and dry-soot ratio in PM, primary and aggregate particle size distributions of PM, activation energy of PM oxidation, and PM components with elemental analysis. As a result, it was shown that ferrocene had special effect on the PM size distribution and the activation energy.

The formation mechanism of Particulate Matter (PM) in a flame and fuel effect on this mechanism, are still under unclear problems. In this study, a fundamental pool combustion flame of diesel fuel was formed and PM emission from the flame was analyzed. As a result, though emission of soot from the flame was not observed, significant number of nuclei mode PM was emitted. From a flame of incomplete combustion, aggregate mode particles increased and nuclei mode particles reduced drastically. When a little mount of lubricant oil was contaminated into diesel fuel, number concentration of nuclei mode particle increased.