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Reduction of fossil fuel consumption is necessary with regards to global warming and energy security. Motorcycle has great potential to play an important role for these demands due to its light weight. Reduction of environmental impact is also an important factor as well as the fuel efficiency. Mixture formation is one of the key issues for both aspects. Port fuel injection system is getting popular due to better control ability of fuel supply than by carbureter that is still used widely due to the benefit of cost and simplicity. Port fuel injection system is widely used for automotive application in many years. Compared to automobile, motorcycle has severe limitations about cost and space. Demand for specific power is higher instead of less stringent emission regulation. Considering these differences, it is important to establish appropriate guide for motorcycle applications with regard to injector layout and injector specification to satisfy regulation for environment without deterioration of advantages. One of the most important issues is generation of wall film. It is enhanced by shorter distance between injection hole and wall against it, shorter duration to evaporate due to higher engine speed, and lower evaporation

Experimental and numerical investigations of shock-compression ignition induced by a disturbance have been carried out. Experiments were performed in a square cross-section shock tube behind reflected shock waves at temperature between 1 401 and 1 681 K and the total densities were kept constant at around 30 mol/m 3. The mixture used was a stoichiometric methane/oxygen/argon with 89.5 percent argon dilution. A thin plate or a fine wire was installed apart from the tube-end of the shock tube to generate density disturbance. The shape of shock-compression ignition flame under different disturbance was observed by direct and schlieren high-speed photography. The disturbance in the shape of a vortex appeared after the reflected shock wave passes through the obstacles. Ignition appears in the vicinity downstream of the obstacle in the tube-end side. The ignition flame is the same shape of the density disturbance. These disturbances made with obstacles promote ignition delay and fixes the position of ignition. The temperature in the disturbed region was evaluated using the temperature-dependent molar extinction coefficients of CO 2 at 220 nm. An infrared absorption method with an infrared He-Ne laser (3.39 µm) was used for measuring the density in the disturbed region. The second order explicit MacCormack-TVD scheme is used to solve two-dimension Navier-Stokes equations. The density of the downstream side of the obstacle is lower than that of the upstream side. Temperature in the disturbed region was higher than others; this high temperature was caused by reflected shock wave acceleration in a rarefaction wave region at the rear of the obstacle.

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