In this book the effort has been done to find the optimal performance and emission characteristics of compression ignition engine.The performance parameters like thermal efficiency,fuel consumption,heat release rate and peak cylinder pressure are analyzed thoroughly. the emissions like carbon monoxide,carbon dioxide,hydrocarbon and smoke are also investigated thoroughly. CNG is a clean and complete burning fuel and Ethanol is a bio fuel, so the blends of both fuels are advised to use in CI engine.Experimentally it is analyzed that the overall performance is increased significantly and harmful and hazardous particles like carbon dioxide,carbon monoxide reduced drastically.Hence it is advisable that CNG and Ethanol blended fuel is the best one for Compressed ignition engines.