Car noun: engine compression ratio

Compression ratio: The ratio of the maximum volume of gas in the cylinder before compression to the minimum volume after compression. The national standard is represented by ε, which is also equal to the ratio of the total cylinder volume to the volume of the combustion chamber. When the gasoline engine is in operation, the mixture of gasoline and air is sucked in. The greater the compression ratio is, the higher the pressure and temperature of the compressed mixture will be. The gasoline molecules in the mixture will be more completely gasified and burn even more. Faster and fuller, the more power the engine emits, the better the economy, and the quality of exhaust gas can be improved accordingly. Conversely, the low compression ratio engine burns relatively longer, increasing energy consumption and reducing power output.

The larger the compression ratio, usually accompanied by an increase in chatter vibration during engine operation (most engines nowadays have undergone special tuning, so this is not very obvious). Excessive compression ratio can not only not improve the combustion situation, but it will appear. "Deflagration" and "surface ignition" and other abnormal combustion phenomena. Deflagration can cause the engine to overheat, reduce power, increase fuel consumption, and even damage the engine. Surface ignition also increases engine load and reduces its life.

In addition, the improvement of the compression ratio is also limited by exhaust pollution regulations. A typical low compression ratio refers to a compression ratio of 10 or less and a numerical value of 10 or more even if it is a high compression ratio engine. The level of the compression ratio has a great influence on the requirements of the gasoline grade of the engine. In general, the greater the compression ratio, the higher the gasoline number required to be used. If gasoline below the recommended number is used, problems such as “knocking”, increased engine vibration, and non-uniform travel may occur, and engine performance and service life may also be impaired. In general, the compression ratio is less than 7.5 can use 90 gasoline, compression ratio of 7.5 to 8.0 should be used 90 or 93 gasoline; compression ratio of 8.0 to 10.0 should be selected 93 or 95 gasoline; compression ratio above 10.0 should be used 97 Gasoline.

Specific to each car, but also take into account some of the actual situation, and the current oil products also have problems, it is not clear, generally use the principle of "on the high is not low", but this does not mean that the higher the gasoline number The better. Because the engine's compression ratio, ignition advance angle and other parameters have already been set at the factory, and a moderate adjustment procedure is set in the computer program against gasoline with poorer detonation, while there is no corresponding program for high-grade gasoline. . Therefore, the blind use of high-grade gasoline is not only a waste of money, but it may also be due to its high anti-knocking strength, which can not be accelerated. The best way is to select the oil number according to the instructions or according to the requirements stated on the fuel tank cover.