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In the twenty-first century, exhaust emission control will remain a major technical challenge especially as additional pressures for fuel and energy conservation mount. To address these needs, a wide variety of engine and powertrain options must be considered. For many reasons, the piston engine will remain the predominant engine choice in the twenty-first century, especially for conventional and/or parallel hybrid drive trains. Emissions constraints favor the conventional port fuel-injected gasoline engine with 3-way exhaust catalyst, while energy conservation favors direct-injection gasoline and diesel engines. As a result of recent technological progress from a competitive European market, diesels, and most recently, direct-injection (DI) diesels now offer driveability and performance characteristics competitive with those of gasoline engines. In addition, DI diesels offer the highest fuel efficiency.

The process of spark ignition of fuel sprays in a rapid compression machine was analyzed using high-speed schlieren photography and pressure-time data. The combustion chamber studied simulates in a two-dimensional sense the three-dimensional arrangement of the piston bowl, injector and spark plug in a typical direct-injection stratified-charge (DISC) engine. The test hardware included a flat-seat straight-hole injector, a high-energy ignition system and an extended-electrode spark plug. The influence of amount of fuel injected, ignition dwell period (time between start of injection and start of ignition), swirl rate and direction, and spark-plug electrode-tip location on the ignition process was examined. For the test conditions studied, excessive spray penetration and fuel impingement on the walls was observed.