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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 expressed as ε it is also equal to the ratio of the total cylinder volume to the combustion chamber volume. When the gasoline engine is running, it is a mixture of gasoline and air. The higher the compression ratio, the higher the pressure and temperature of the compressed mixture. The gasoline molecules in the mixture can be more completely vaporized and burned. It is faster and more complete, so the greater the power generated by the engine, the better the economy, and the improved exhaust quality. Conversely, a low compression ratio engine burns time is relatively extended, increasing energy consumption and reducing power output.
The larger the compression ratio, the higher the chattering is usually when the engine is working. (The current engine is mostly adjusted, so it is not very obvious.) The compression ratio is too large, not only can not further improve the combustion situation, but will appear Abnormal combustion phenomena such as "explosion" and "surface ignition". Deflagration can cause the engine to overheat, reduce power, increase fuel consumption, and even damage the engine. Surface ignition also increases the load on the engine, reducing its life.
In addition, the increase in compression ratio is also limited by exhaust pollution regulations. The usual low compression ratio means that the compression ratio is below 10, and the value above 10 is even a high compression ratio engine. The compression ratio has a great influence on the requirements of the engine to use the gasoline grade. Generally speaking, the larger the compression ratio, the higher the gasoline label required. If gasoline below the recommended number is used, it may cause problems such as “knocking”, increased engine vibration, uneven speed, etc., and may impair engine performance and shorten service life. Generally, the compression ratio is lower than 7.5, the 90th gasoline can be used, the compression ratio should be 90 or 93 gasoline in the compression ratio of 7.5 to 8.0; the compression ratio should be 93 or 95 gasoline in the compression ratio of 8.0 to 10.0; the compression ratio should be 97 or higher. No. Gasoline.
Specific to each car, but also to consider some actual conditions, and the current oil products are also problematic, it is unclear, generally adopt the principle of "high or low", but this does not mean that the higher the gasoline mark The better. Because the engine's compression ratio, ignition advance angle and other parameters have been set at the factory, and in the computer program against the poorly explosive gasoline set a moderate adjustment program, but there is no corresponding procedure for high-grade gasoline . Therefore, the blind use of high-grade gasoline is not only a waste of money, but also may be accelerated due to its high anti-explosive advantage. The best way is to select the oil number according to the instructions or according to the requirements indicated on the fuel tank cap.