Fuel Injection System of Air-cooled Engines for Small Displacement Motorcycles

With the interest in global environmental issues growing in recent years, the demand for the reduction of exhaust gas emission and improvement in fuel consumption for small motorcycles has increased greatly. Recently, small motorcycles have been marketed equipped with an electronically controlled fuel injection system effective in reducing emissions and enhancing fuel consumption by accurately controlling the air-fuel ratio. The small motorcycles' market comprises mainly ASEAN countries, and the majority of the motorcycles consist of reasonably priced models with air-cooled engines. Fuel injection systems have already been adopted for motorcycles equipped with water-cooled engines in the markets of advanced countries, mostly in EU. Given the above situation, two issues must be addressed to adopt a successful fuel injection system for air-cooled, low-priced small motorcycles. First, the fuel injection systems' components must be protected from the thermal influence of air cooled engines. Due to higher ambient temperatures around the air cooled engine as compared to the water-cooled engine, vaporization of fuel must be prevented. Second, the cost of the fuel supply system must be minimized to permit manufacturing of a low price motorcycle. The developed fuel injection system has addressed above-mentioned issues with modifications of the major component parts of the fuel feed system, the fuel pump module, high-pressure fuel piping and injector, and by eliminating the return pipe from fuel feed system. This paper presents details of design technologies employed to create each component and the results obtained from a performance test of a comparing vehicle, 125 cm³ motorcycle.