The maximum volume of the cylinder at the bottom dead center than the minimum cylinder volume at top dead center, that is the compression ratio.
Why should gas pressure
This is because: increased pressure allows the gas density becomes large, the distance between the molecules also becomes smaller, so that the fuel and oxygen molecules also closer distance, the combustion speed is faster; temperature allows gas molecules moving speed, fuel and oxygen molecules interact more easily, This make it easier to ignite a gas mixture. And the smaller the combustion space can be completed faster combustion, combustion speed up the process also improves performance.
Although modern gasoline engine compression ratio is getting higher and higher, but this is the continuous development in science and technology to enhance the lower and higher and higher gasoline label premise. After all, this is a process, not overnight. Early engine technology is not advanced, the cylinder can not bear too much pressure, and even allows the engine, there are also no high-grade gasoline or oil is not popular, such as 212 and 2020 of the eighties and nineties, the compression ratio only seven a few, can burn No. 75 oil even lower, and the introduction of Cherokee less than 85 gasoline will not work properly. And for the diesel engine, the greater the compression ratio is also bound to have a higher pressure, the robustness of the partsIt is a test.
Therefore, under normal circumstances, the same displacement of the engine, the higher the compression ratio, its power and the better the economy. But there are degrees of everything, the pursuit of high performance and simple to improve the compression ratio, but also to their normal work, the difficulty is multiplied exponentially. And the current domestic oil really not very good, but also limiting the promotion of some of the best engines in the country.