An engine is a complex machine composed of many mechanisms and systems. Whether it is a gasoline engine or a diesel engine; Whether it is a four stroke engine or a two stroke engine; Whether it is a single cylinder engine or a multi cylinder engine. To complete energy conversion, achieve work cycles, and ensure long-term continuous normal operation, the following mechanisms and systems must be in place.
(1) Crank connecting rod mechanism
The crank connecting rod mechanism is the main moving part of the engine that realizes the working cycle and completes energy conversion. It consists of a body assembly, a piston connecting rod assembly, and a crankshaft flywheel assembly. During the power stroke, the piston undergoes a linear motion in the cylinder under gas pressure, which is converted into the rotational motion of the crankshaft through the connecting rod, and outputs power from the crankshaft to the outside. During the intake, compression, and exhaust strokes, the flywheel releases energy and converts the rotational motion of the crankshaft into the linear motion of the piston.
(2) Valve distribution mechanism
For a four-stroke engine, The function of the valve distribution mechanism is to regularly open and close the intake and exhaust valves according to the working sequence and process of the engine, allowing combustible mixture or air to enter the cylinder and exhaust gas from the cylinder, achieving the air exchange process. The valve train mostly adopts an overhead valve train, which is generally composed of a valve group, a valve transmission group, and a valve drive group.It is somewhat different for two-stroke engines, as this type of engine does not have a valve train structure. The fuel mixed with air will enter the cylinder through a special airway structure inside the cylinder.
(3) Fuel supply system
The function of the gasoline engine fuel supply system is to prepare a certain amount and concentration of mixture according to the requirements of the engine, supply it to the cylinder, and exhaust the burned exhaust gas from the cylinder to the atmosphere; The function of the diesel engine fuel supply system is to separately supply diesel and air into the cylinders, form a mixture in the combustion chamber and burn it, and finally exhaust the burnt exhaust gas.
(4) Lubrication system
The function of the lubrication system is to deliver a quantitative amount of clean lubricating oil to the surface of parts in relative motion, in order to achieve liquid friction, reduce frictional resistance, and reduce the wear of machine parts. And clean and cool the surface of the parts. For a four-stroke engine,the lubrication system usually consists of lubricating oil ducts, oil pumps, oil filters, and some valves. For a two-stroke engine, a certain ratio of oil and gasoline is mixed to make the fuel, which can automatically lubricate the internal parts of the engine by sucking in fuel during operation. Therefore, maintenance is relatively simple, and there is no need to specifically use lubricating oil for additional maintenance of engine parts.
(5) Cooling system
The function of the cooling system is to timely dissipate some of the heat absorbed by the heated parts, ensuring that the engine operates at the most suitable temperature state. The cooling system of a water-cooled engine usually consists of a cooling water jacket, water pump, fan, water tank, thermostat, etc.
(6) Ignition system
In a gasoline engine, the combustible mixture in the cylinder is ignited by an electric spark. Therefore, a spark plug is installed on the cylinder head of the gasoline engine, and the head of the spark plug extends into the combustion chamber. All equipment that can generate electric sparks between the spark plug electrodes on time is called the ignition system, which usually consists of a battery, generator, distributor, ignition coil, and spark plug.
(7) Starting system
To transition the engine from a stationary state to a working state, it is necessary to first use external force to rotate the engine's crankshaft, causing the piston to move back and forth. The combustible mixture in the cylinder burns and expands to work, pushing the piston downward to rotate the crankshaft. The engine can only run on its own and the working cycle can be carried out automatically. Therefore, the entire process of the crankshaft starting to rotate under external force until the engine starts to automatically idle is called engine starting. The device required to complete the starting process is called the starting system of the engine.
(8) Difference
The commonly used piston type aviation model engines include 2-stroke and 4-stroke engines. Although the operating principle is basically the same, there are still many differences between the two engines. More intuitively, the 2-stroke engine has a relatively simple structure, easy maintenance, and a relatively large thrust weight ratio; The four stroke structure is complex and relatively difficult to maintain, but it has good stability and is also fuel-efficient.
In general, for the selection of piston-type aircraft model engines, it is necessary to choose the appropriate displacement engine and different stroke engines based on the aircraft model and size. Only the most suitable engine can bring the most perfect experience to flight.
