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With the introduction of increasingly more stringent emission standards, Engine Management Systems (EMS), including port fuel injection, are now being introduced in the 4-stroke motorcycle marketplace. These systems have been generally derived from the automotive industry, albeit with some significant changes to satisfy the strict cost and packaging constraints of the motorcycle applications. Direct injection (DI) is positioned to become one of the next generation of technologies for the automotive engine, offering the potential for improved fuel economy, performance and emissions control. Direct injection can also provide similar benefits for motorcycle applications. However, direct transfer of the current production automotive systems is unlikely to suit the requirements of motorcycle applications, due to some of the specific challenges faced in the motorcycle market.

Orbital have been developing their stratified combustion process (Orbital Combustion Process OCP) for direct injection gasoline engines over the last 15 years, with successful production releases of the system in both the marine and automotive 2-stroke applications in 1996. This paper discusses how the same basic qualities of the air-assist fuel system and combustion process have been applied to automotive 4-stroke engines. The inherent qualities of the air- assist fuel system in combination with careful design of the combustion chamber has enabled high charge stratification with late injection timings and very stable combustion over a wide range of operating conditions. Experimental test data from a 4-cylinder, 16 valve 4-stroke development engine demonstrates the ability of this low pressure system to operate at very lean air/fuel ratios, with part load fuel economy improvements of up to 34 % at an operating condition equivalent to a vehicle speed of 40 km/hr.