As a common engine for small general-purpose aircraft, the aviation piston engine converts about 30% of the heat released by fuel combustion into effective work to drive the propeller to generate tension, 45% of the heat is lost to the atmosphere with the exhaust gas, and another 25% is taken by the coolant. Into the atmosphere. Most light horizontally opposed engines and radial engines often use the atmosphere flowing past the engine as their external cooling medium, and there is no internal cooling, known as an air cooled engine. The application of this design is also for this type of engine.
The mechanism that controls the engine's external coolant flow to keep the cylinder temperature within the specified range is called the heat dissipation system (or cooling system) and is divided into fixed and adjustable. Improper cooling affects the engine. The engine's gas temperature can reach up to 2500 ° C ~ 3000 ° C. Parts that are in contact with high temperature gas, such as cylinder head, valve, electric nozzle and piston, are also very hot due to heat conduction. . Some serious consequences can occur if not properly cooled.
If the cooling medium flow is too small, the engine cooling effect is poor, the cylinder temperature will be too high, the material strength will be significantly weakened, and the cylinder and its closely connected parts will be easily under the action of dynamic load and heat load. Damage, such as cylinder head wrinkles, cracks, piston top burn-through, valve deformation, cracks, etc. At the same time, the gap between the piston and the cylinder wall, the gap between the rising ring and the rising ring, and the gap between the valve stem and the valve stem sleeve may also cause decomposition and oxidation of the lubricating oil in the piston ring to form a gelatinous substance. Sticking to the ring, affecting the lubrication of the cylinder wall, and even grinding and burning the piston.