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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.

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.

The objective of this paper is to summarize experimental results which were previously reported by the authors and to derive many useful empirical equations concerning the diesel fuel sprays. The empirical equations for break-up length, spray angle, spray tip penetration and drop size distribution of the diesel sprays are introduced to discuss the internal structure of the spray. According to the effect of injection pressure and ambient pressure on the break-up length and drop size of the diesel spray, the spray structure can be divided into two categories; incomplete and complete sprays. The equations which express the break-up length and mean diameter of the incomplete and complete sprays were obtained using different techniques according for the dominance of one or more break-up mechanisms.

Effects of fumigated fuel on the initial combustion stage of a diesel spray were studied by measuring an ignition delay period and rate of heat release, clarifying a self-ignition limit of a fumigated fuel. Combustion experiments on both fumigated diesel fuel and methanol in a direct injection diesel engine gave the following results; a rapid combustion occurs with the methanol fumigation, while, the diesel fuel fumigation slightly changes the combustion of the main spray of diesel fuel injected directly into the combustion chamber. Regarding the rate of heat release, the maximum rate in the initial combustion stage increases rapidly with an increase in methanol fumigation, while for the fumigated diesel fuel, the maximum rate changes only slightly. The ignition delay period affected by fumigated diesel fuel is shorter than that affected by methanol at the same fumigation equivalence ratio and intake temperature.

A six-stroke DI diesel engine proposed by the authors had second compression and combustion processes which were added on a conventional four-stroke diesel engine. This engine had the first and second power strokes before the exhaust stroke. Numerical predictions and experiments previously carried out had shown that this six-stroke diesel engine could reduce NO exhaust emission. Further, the ignition delay of the second combustion process could be shortened by a high temperature effect in the second compression stroke. This advantage of short ignition delay could be utilized for an ignition improvement of a fuel with low cetane number. In the engine system reported here, a conventional diesel fuel was supplied as the fuel of first combustion process, and in the second combustion process, methanol was supplied.

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.