(1) The four-stroke gasoline engine mixes air and gasoline in a certain proportion to form a good mixture of automobile engines. In the intake stroke, the mixed gas is sucked into the cylinder, and the mixed gas is compressed, ignited and burned to generate heat energy. High temperature and high pressure gas acts on the top of the piston, pushing the piston to do linear reciprocating motion, and mechanical energy is output through connecting rod, crankshaft and flywheel mechanism. A four-stroke gasoline engine completes a working cycle in the intake stroke, compression stroke, power stroke and exhaust stroke. (2) The intake stroke piston is driven by crankshaft and moves from top dead center to bottom dead center. At this time, the intake valve opens, the exhaust valve closes, and the crankshaft rotates 180. During the movement of the piston, the volume of the cylinder gradually increases, the gas pressure in the cylinder gradually decreases from pr to pa, and a certain degree of vacuum is formed in the cylinder. The mixture of air and gasoline is sucked into the cylinder through the intake valve and further mixed in the cylinder to form a combustible mixture. Due to the resistance of the intake system, at the end of intake, the gas pressure in the cylinder is less than the atmospheric pressure p0, that is, Pa=(0.80~0.90)P0. Due to the heating of high-temperature components such as intake pipe, cylinder wall, piston crown, valve and combustion chamber wall, and the mixing with residual exhaust gas, the temperature of combustible mixture entering the cylinder rises to 340 ~ 400 k k (3). During the compression stroke, the intake valve and exhaust valve are closed at the same time. When the piston moves from bottom dead center to top dead center, the crankshaft rotates 180. When the piston moves upward, the working volume decreases gradually, and the pressure and temperature of the mixture in the cylinder increase continuously after being compressed. After the compression, the pressure pc can reach 800~2000kpa and the temperature can reach 600 ~ 750 K (4). When the piston approaches the top dead center, the spark plug ignites the combustible mixture, and the combustion of the mixture releases a lot of heat energy, which makes the pressure and temperature of the gas in the cylinder rise rapidly. The highest combustion pressure pZ is 3000~6000kPa and the temperature TZ is 2200 ~ 2800 K. The high-pressure gas pushes the piston to move from the top dead center to the bottom dead center, and the mechanical energy is output through the crank-connecting rod mechanism. As the piston moves down, the volume of the cylinder increases, and the gas pressure and temperature gradually decrease. When it reaches point B, the pressure drops to 300~500kPa and the temperature drops to 1200~ 1500KK. During the power stroke, the intake valve and exhaust valve are closed and the crankshaft rotates 180. (5) Exhaust Stroke During the exhaust stroke, the exhaust valve is opened, the intake valve is still closed, the piston moves from the bottom dead center to the top dead center, and the crankshaft rotates 180. When the exhaust valve is opened, the burnt exhaust gas is discharged to the outside of the cylinder under the pressure difference between the inside and outside of the cylinder, on the other hand, it is discharged to the outside of the cylinder through the squeezing action of the piston. Due to the resistance of the exhaust system, the pressure at the exhaust end R is slightly higher than atmospheric pressure, that is, PR=( 1.05~ 1.20)P0. The exhaust temperature tr = 900 ~1100 K. When the piston moves to the top dead center, there is still a certain volume of exhaust gas in the combustion chamber. This part of waste gas is called residual waste gas.