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As boosted, direct injected gasoline engines become more prevalent in the automotive market, the boosting system architecture and efficiency are intimately entwined with the efficiency and performance of the engine. Single-stage as well as two-stage boosting systems, comprising of either two turbochargers or a supercharger in combination with a turbocharger, are potential configurations. When combining an internal combustion engine with boosting hardware, a mechanical, fluid-dynamic and thermodynamic coupling is created and the system as a whole will need to be treated as such.

Downsizing is an important concept to reduce fuel consumption as well as emissions of spark ignition engines. Engine displacement is reduced in order to shift operating points from lower part load into regions of the operating map with higher efficiency and thus lower specific fuel consumption [ 1 ]. Since maximum power in full load operation decreases due to the reduction of displacement, engines are boosted (turbocharging or supercharging), which leads to a higher specific loading of the engines. Hence, a new combustion phenomenon has been observed at high loads and low engine speed and is referred to as Low-Speed Pre-Ignition or LSPI. In cycles with LSPI, the air/fuel mixture is ignited prior to the spark which results in the initial flame propagation quickly transforming into heavy engine knock. Very high pressure rise rates and peak cylinder pressures could exceed design pressure limits, which in turn could lead to degradation of the engine.

Southwest Research Institute® (SwRI®) has developed electronic fuel injection (EFI) systems to be used on air-cooled motorcycle applications. In order to explore differences in application requirements between large and small displacement motorcycles, a large twin-cylinder, four-stroke, air-cooled motorcycle, and a small single cylinder, four-stroke, air-cooled motorcycle were utilized. The primary objectives of this study were to meet current and future emissions regulations for motorcycle exhaust emissions, to raise fuel economy, and to improve overall engine performance. The EFI development required baseline testing, control system setup, design of intake system components, installation of sensors and control unit, fuel system integration, steady-state and transient calibration, fuel consumption development, emissions development, performance improvement, and acceleration testing.