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The direct injection (DI) gasoline engine has drawn considerable attention recently for energy savings and emission reductions. Compared with current port fuel injection (PFI) engines, DI engines are designed to have high specific power output, low fuel consumption and low emissions at the same time. Among others a feature of the DI gasoline engine is its capability to freely alter the state of combustion from homogeneous to stratified combustion at different load conditions. Engines with high power density such as the DI engine, are also prone to knock. To suppress engine knocking a flexible and precise combustion control mechanism is required. The paper being presented describes some of the characteristics required for spark plugs utilized in DI gasoline engines.

NGK Spark Plug has developed new Multi Spark Ignition (MSI) system to improve fuel economy and engine cold start performance. Since engine ignition is the very first stage of reaction process, which leads to subsequent combustion and emission formations, it plays an important function to determine the efficiencies of power conversion and characteristics of exhaust gas. In addition to the conventional function of combustible gas ignition, the spark plug detects ion current surrounding the plug gap to analyze state of combustion. The developed MSI system demonstrated significant performance advantages on engine ignitions and detection of combustion characteristics for engine optimal control.