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Performances of gasoline engine fueled by gasoline into cylinder and pure hydrogen or simulated reformer gas (H2, CO, CO2, and CH4) into intake manifold were evaluated in view of improvement of thermal efficiency of spark ignition engine. Commercial spark ignition direct injection gasoline engine was modified to install injection system of commercial CNG vehicle. Test engine can be controlled by homogeneous and stratified charged combustion for gasoline. Thermal efficiency of the engine operated with gasoline and hydrogen or reformer gas is much higher than that with gasoline under low and mid load conditions. Especially the improvement of thermal efficiency with gasoline and hydrogen on lean burn condition is less than 40% that with gasoline on stichometric condition under low load condition. The operating range of the engine operated with hydrogen is limited due to knocking, but the range is extended by the addition of gasoline.

The effects of injector deposits, combustion chamber deposits (CCD), and intake valve deposits (IVD) on exhaust emissions, fuel economy and engine performance have long been recognized in engine and fuel/detergent design. Because important elements of the engine design such as injector position, exhaust gas recirculation (EGR) ratio, and air fuel ratio (AFR) differ from those in port fuel injection (PFI) engines, direct injection spark-ignition (DISI) engines require specific evaluation methods. However, little data is available regarding engine deposits in the more recently produced DISI engines.