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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.

Until the early to mid 1990's the engine of choice for off road and recreational vehicles were mainly 2-stroke engines due to the superior power density and Wide Open Throttle (WOT) torque characteristics. With the introduction of increasingly more stringent emission control requirements there has been a large swing to 4-stroke engines. In recent years there has been significant development to improve the power density of the 4-stroke engine in an effort to match the performance 2-stroke engine, however at a compromise to the torque characteristics and the manufacturing and maintenance cost of the engine. This paper looks at a fresh approach to develop a new concept engine to deliver a better compromise between the 4-stroke and existing carburettor 2-stroke characteristics, and provides early experimental results from the development work for a preferred WOT torque characteristic.

Whilst Direct In-cylinder injection is now common in both the automotive and non-automotive markets, the very high performance 2-stroke engines pose specific challenges to the application of direct injection due to the increased fuelling levels, the high fuel turn down ratio requirements and the reduced fuel preparation times at high engine operating speeds. In addition, a high performance 2-stroke engine will usually have a highly tuned scavenging system, which puts further demands on the fuel and combustion systems to achieve the desired performance. The fuel and combustion systems must also retain the low emissions to meet the relevant emissions legislation with a minimum level of aftertreatment.