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Particulate matter (PM) emission from direct-injection (DI) gasoline engines are caused by pool combustion of fuel adhering on a piston wall. It is necessary to clarify the formation process of liquid fuel film. In this study, temporal change of fuel mass adhered on the wall was evaluated to understand the adhesion process of a liquid fuel film by using total internal reflection laser-induced fluorescence (TIR-LIF) technique. As a result, the mass of the liquid film increased during the fuel injection period, and it decreased rapidly during the period that spray tail after the end of injection reached the wall surface.

A glow plug is the promising way for improvement for ignition of fuel under cold start condition in high-speed diesel engines. The configuration of a glow plug and a diesel spray in a combustion chamber is important factor to maintain ignitability of fuel at cold start. In this study, flow structure of the spray interfered with a circular cylinder instead of the glow plug was investigated by changing of location of the circular cylinder with respect to the spray. As results, the vortex around the circular cylinder was formed with interference of the spray with the circular cylinder, and appearance position of its vortex was related to interference position of the spray periphery with the circular cylinder was clarified.

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.

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.

Impingement of a spray flame on the periphery of the piston cavity strongly affects heat loss to the wall. The heat release rate history is also closely correlated with the indicated thermal efficiency. For further thermal efficiency improvement, it is thus necessary to understand such phenomena in state of the art diesel engines, by observation of the actual behavior of an impinging spray flame and measurement of the local temperature and flow velocity. A top-view optically accessible engine system, for which flame impingement to the cavity wall can be observed from the top (vertically), was equipped with a high speed digital camera for direct observation. Once the flame impinged on the wall, flame tip temperature decreased roughly 100K, compared to the temperature before impingement.

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.