What is Engine Compression Ratio?
1 Answers
Engine compression ratio is the ratio of the volume of the cylinder before compression to the volume of the compressed air-fuel mixture, which is the ratio of the maximum volume of the cylinder when the piston is at the bottom dead center to the volume of the cylinder when the piston is at the top dead center. Engine operation process: Engines operate on a four-stroke cycle, consisting of intake, compression, power, and exhaust strokes. During the intake and power strokes, the piston is at the bottom dead center position, while during the compression and exhaust strokes, the piston is at the top dead center position. For example, if the cylinder volume is 10 when the piston is at the bottom dead center and the compressed mixture volume is 1 when the piston is at the top dead center, the engine compression ratio is 10:1. Impact of compression ratio on engine performance: Higher engine compression ratio: If the engine has a higher compression ratio, the air-fuel mixture is compressed under greater pressure and at a relatively higher temperature. The gasoline in the mixture vaporizes more completely and is easier to ignite. When the spark plug fires after full compression, more energy is released in a very short time. This energy is then transmitted to the wheels through the piston, crankshaft, and other mechanisms, becoming the driving force for the car. Lower engine compression ratio: In engines with a lower compression ratio, gasoline molecules do not vaporize completely. Therefore, after the spark plug fires, the combustion speed is relatively slower, and some energy is converted into heat, causing the engine temperature to rise instead of being fully converted into the car's kinetic energy. Thus, for the same cylinder volume, a higher compression ratio results in greater power output. The engine compression ratio is not the higher the better, but should be appropriate. An excessively high compression ratio can reduce stability and shorten the engine's lifespan.
