Why does gasoline combustion produce high-pressure gas? Why does the heat released by combustion cause the pressure and temperature of gas to rise sharply during the power stroke of diesel engine?

From the names of the two engines, we can see what they eat, that is, gasoline and diesel, and both gasoline and diesel are composed of hydrocarbons, including carbon and hydrogen. Gasoline is composed of hydrocarbons with 5-9 carbon molecules, while the carbon number of hydrocarbons that make up diesel is 10-20. Because gasoline molecules are smaller than diesel, gasoline is more volatile and burns faster. We regard gasoline as a pile of catkins, which can be blown away in the air and fall slowly, while diesel is like a piece of wood, which will fall freely when thrown out. Gasoline engines ignite because gasoline has a high ignition point, but high volatility and low flash point. In the process of compression, the heat generated by compression is absorbed by gasoline, which gasifies. The spark plug ignites mainly gasoline vapor, and most gasoline gasifies and burns at high temperature, mainly gas. The carbon chain of diesel oil is longer than that of gasoline, so it is not easy to volatilize. However, due to the long carbon chain, diesel oil is easy to oxidize, so its ignition point is lower than that of gasoline. To make diesel spontaneously ignite, it needs a high compression ratio to generate a lot of heat, and the distance between air molecules is smaller, which makes diesel more likely to contact with oxygen in the air. Therefore, in order to be unnatural, pure air is inhaled, and no fuel is involved in the compression process. During the ignition process, diesel oil is injected into the cylinder through the high-pressure fuel injection pump, and the diesel oil is rapidly atomized in the cylinder in high-temperature and high-pressure air, and burns in many places at the same time to form a flame. That is to say, work is done by deflagration (similar to the "knock" of gasoline engines), and the working state is relatively rough. But because diesel fuel burns slowly, unlike gasoline engine knocking, because gasoline engine burns gas when knocking, and the combustion speed is too fast.