Today's engines are mainly internal combustion models, which can convert the thermal energy generated by fuel combustion into mechanical energy. The reason why the internal combustion engine is widely used is mainly due to its several characteristics and advantages: small volume and weight, easy assembly, of course, this is based on the continuous improvement of people; the power generated is strong and stable, and the number of cylinders can be increased or decreased according to the requirements of the equipment; after continuous improvement, the economy is better. Of course, there must be advantages and disadvantages; the internal combustion engine's structure is precise and complex, the internal operating conditions are poor, and the probability of failure is high. In addition, its operation needs to consume a large amount of air and discharge harmful exhaust gases, which has an adverse impact on the environment, becoming the biggest bottleneck for its continued development. Although engine technology, lubricant technology, and fuel refining technology are becoming more sophisticated, they cannot completely solve the environmental problems caused by internal combustion engines. The internal combustion engine should have been born in the second half of the 19th century; before that, the steam engine, as the most powerful artificial power source at that time, had been widely used in Western industry and the shipping industry, but its huge mechanism and low thermal efficiency and other problems are also obvious. With the improvement of thermodynamic theory and the development of industrial bases such as steel refining and the petroleum refining industry, the birth of the internal combustion engine has become an inevitable trend.

Over the past 100 years, various types of internal combustion engine engines have been invented and manufactured, but their main structures and principles have not changed much. In terms of piston movement mode, there are mainly reciprocating and rotary types, and reciprocating internal combustion engines are divided into two-stroke and four-stroke; in terms of fuel use, it is mainly divided into steam engine oil engine and diesel engine oil engine, and its ignition mode is different, the steam engine oil engine is mainly ignition type, and the diesel engine engine is mainly compression ignition; in addition, with the continuous improvement of people's power requirements, the single-cylinder engine has been unable to meet the requirements, and the multi-cylinder engine came into being, and the multi-cylinder engine can be divided into different arrangements such as in-line and V-type. Furthermore, with the continuous improvement of people's requirements for automobile power, the supercharged engine is becoming increasingly widespread, and the difference between it and the ordinary engine is the air intake mode; the supercharged engine uses a supercharger to enhance the air intake density, which can boost the power of the engine.

The development of the internal combustion engine to this day has seen its main internal structure remain basically fixed. According to the information queried by the author, it mainly includes: crank connecting rod mechanism, gas distribution mechanism, fuel supply system, cooling system, lubrication system, ignition system, and starting system. The crank connecting rod mechanism is a set of mechanisms that transmit the reciprocating motion of the piston to the crankshaft and convert thermal energy into mechanical energy. The gas distribution mechanism mainly refers to a set of mechanisms that provide the air required for engine combustion and exhaust gas. The fuel supply system serves to transport fuel to the cylinder in a certain way for combustion. In this regard, there is a significant difference between petrol engines and diesel engines; most petrol engines mix fuel and air before transporting to the cylinder, whereas diesel engines transport fuel and air to the cylinder separately. The cooling system, as the name suggests, dissipates part of the heat generated by the engine to prevent it from overheating. The lubrication system delivers lubricating oil to the surface of each part of the engine to achieve lubrication and wear reduction, cleaning and decontamination, heat transfer, and cooling, allowing the engine to maintain a good running state for a certain period. The ignition system mainly refers to a set of systems that ignite the gas mixture in the cylinder; the ignition system of a standard petrol engine usually consists of batteries, generators, ignition coils, spark plugs, and other components. The starting system of the engine refers to a set of systems that promote the smooth reciprocating motion of the piston by applying a certain external force to the crankshaft and reaching a specific speed, which mainly comprises electric motors and other devices.

The power of the engine comes from the reciprocating motion of the piston. As far as the four-stroke engine is concerned, it contains four strokes, namely air intake, compression, work and exhaust. These four strokes constitute a complete working cycle, in which air intake, compression and exhaust are energy-consuming strokes, and only the power stroke can make the engine generate power. The generated power is transmitted to the flywheel through the crankshaft.

The internal combustion engine has been widely used by human beings for more than 100 years, and its emergence has greatly promoted the development of equipment mechanisation and automation and various vehicle and ship power devices, greatly improved the efficiency of labour, production and life, completely changed the way human beings use and convert energy, and greatly promoted the development of human modernisation.

（Due to the limited knowledge and English proficiency of the author, it is inevitable that there will be mistakes, inappropriate or problematic expressions, and readers are expected to correct them. Some of the information in this article comes from the Internet, and this article is only for learning and reference purposes.）