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Recently, the use of ethanol blended fuel is growing worldwide. Therefore, there is increasing needs for addressing issues relating to ethanol blended fuel use in gasoline engine fuel supply systems. In this paper, we focused on one of such issues, which is the reduced life of a multi-layered fuel filter used at inlet side of a fuel pump when it is used with ethanol blended fuel. In this study, we clarified that ethanol blended fuel tends to disperse dust particles contained in fuel to a greater extent than gasoline, and that it has a mechanism to accelerate clogging by concentrating the clogging only on the finest layer of the multi-layered filter. Also, in the process of clarifying this principle, we confirmed that dust particles dispersed by ethanol are coagulated when passing through the filter layers.

Recently, the electronic fuel injection systems have been widely applied to small motorcycles including scooters. In the high pressure fuel lines, plastic hoses have been increasingly used instead of conventional rubber hoses. As the plastic hose is less elastic than the rubber hose, the fuel pressure pulsates more in the plastic hose. To cope with this issue, we have conducted researches on how the fuel pressure pulsation in the plastic hose affects the accuracy of fuel injection. Keeping our eyes on the pulsation damping effects derived from the changes of volume due to the expansion and contraction of hose when the pressure changes, we have established the analysis method for optimization of the inner diameter and the thickness of the hose utilizing CAE analysis. The newly-developed plastic hose is applicable to motorcycles having a single cylinder 250 cm3 engine using an injector of a high static flow rate.