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For handheld power tools, a four-stroke engine allows compliance with exhaust emissions regulations although four-stroke engines available tend to have unfavorable power to weight. The requirement for a low cost diecast block compromises valve sizes and port flow. While dynamic valve train limitations restrict maximum engine speeds. The use of a rotary valve as opposed to poppet valves avoids these issues and results in an engine with competitive performance. The engine block can be diecast and the engine can operate up to 14,000 rpm without valve related issues. This paper describes the evolution of a rotary valve concept and its application to two 35cc handheld development engines. The HRCV35 is based on a belt driven rotary valve horizontally mounted parallel to the crankshaft axis. The VRCV35 is based on a gear driven rotary valve vertically mounted on the cylinder axis. In both configurations, the rotary valve exposes inlet and exhaust ports providing unrestricted flow.

In the automotive industry, computer simulation techniques have been developed to improve the 4-stroke engine development process. The objectives are to reduce engine development time, optimise engine performance, improve refinement, and to achieve legislative noise and emissions requirements. The application of these methods to a 4 stroke scooter engine has been evaluated. This paper describes how computer simulation techniques have been used to assist with the development of a new 125cc 2 valve 4 stroke scooter engine built by Piaggio Veicoli Europei Spa, and to evaluate an advanced 4-stroke scooter engine concept. A single dimensional fluid dynamic analysis code WAVE has been used to simulate engine performance and inlet/exhaust noise during prototype development. To support this analysis, pseudo-static valve train analysis using a multi-polynomial camshaft design approach has been used to optimise valve train performance.

A preliminary test bed evaluation of a potentially simple and low cost stratified charging concept is presented for small capacity 2-stroke scooter engines. The end development objectives of the concept are to reduce engine out hydrocarbon emissions and to improve fuel economy while providing engine fuelling by a simple carburettor type fuel metering device. Such a concept, when combined with a catalyst, could achieve significant vehicle emissions reductions with potentially improved catalyst durability. The results presented in this paper, from a preliminary test bed evaluation of the stratified charging concept using electronic fuel injection to provide the fuelling, have shown that engine out hydrocarbon emissions can be effectively reduced at medium to high load without a loss in wide open throttle torque.