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Design of a Direct Injection Retrofit Kit for Small Two-Stroke Engines
Published October 12, 2005 by Society of Automotive Engineers of Japan in Japan
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Carbureted 2-stroke engines are a worldwide pandemic. There are over 50 million 2-stroke cycle engines in Asia alone, powering motorbikes, mopeds, “three-wheelers”, “auto-rickshaws”, “tuk-tuks”, and “tricycles”. These carbureted 2-stroke engines are characterized by high levels of hydrocarbon (HC), carbon monoxide (CO), and particulate matter (PM) emissions. Direct injection is a technology that has shown a great ability to reduce these emissions while at the same time improve fuel economy. A prototype kit has been designed for use in retrofitting existing carbureted two-stroke engines to direct injection. The kit was designed for use on a Kawasaki HDIII; a motorcycle from the Philippines that is commonly used as a taxi. It is however, a relatively common engine design and Kawasaki manufactures similar models for sale all over the world. The retrofit kit incorporates the Orbital air blast direct injection system. This injection system has been implemented in Original Equipment Manufacturer (OEM) applications for over six years. The design involved replacing the existing cylinder head with one designed to incorporate the direct injection valves as well as a modified combustion chamber. An external compressor was added to supply compressed air to the system. The carburetor was replaced with a throttle body outfitted with a position indicator, and an encoder system was added to provide speed and position feedback to the engine control unit (ECU). Once design and manufacture of the system was complete, it was installed on the motorcycle. The motorcycle was then mounted in a low inertia eddy current dynamometer test cell for calibration. Calibration was done on the dynamometer for power and engine performance. The system was also tuned in real world road tests for drivability. When calibrations were complete emissions and fuel consumption measurements were taken for the vehicle. The results showed an 88% reduction in hydrocarbon emissions and a 72% reduction in carbon monoxide emissions versus the baseline engine, while at the same time virtually eliminating visible smoke. The retrofitted system also showed a 32% increase in fuel economy, and had similar to better performance than the carbureted engine. The retrofitted system also showed improved cranking and idling characteristics over the carbureted engine.
CitationLORENZ, N., BAUER, T., and WILLSON, B., "Design of a Direct Injection Retrofit Kit for Small Two-Stroke Engines," SAE Technical Paper 2005-32-0095, 2005.
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