Diesel engine

The use of gasoline engines is indeed very extensive. Whether it is small tools such as lawn mowers that are often used in production or vehicles such as motorcycles and cars, there are gasoline engines. However, for heavy machinery such as trucks and ships, gasoline engines are far from enough. Here we need to use the diesel engine explained today.

The difference between diesel engines and gasoline engines

After Karl Benz (the founder of Mercedes-Benz) invented the first gasoline engine in 1879, Diesel, also a German, invented the first diesel engine in 1892. Although both are internal combustion engines, there are still many differences between diesel engines and gasoline engines, which is determined by the characteristics of diesel. Compared with gasoline, diesel is not easy to volatilize, and the carburetor used in the original gasoline engine cannot be used to vaporize diesel and mix it with air to enter the cylinder for combustion. Therefore, diesel is directly injected into the cylinder by the injector. Since diesel is not easy to ignite, the electric spark generated by the spark plug cannot effectively ignite diesel. The diesel engine uses the high temperature and high pressure generated by the piston compressing the gas in the cylinder during the compression stroke to ignite the diesel. This can be explained by the law of conservation of energy. During the compression stroke, the outside world does work on the gas, which increases the internal energy of the gas and raises the temperature.

Compared with gasoline engines, diesel engines can use diesel from a wider source and at a lower cost, and can also output greater torque at a lower speed. In other words, diesel engines can drive heavier machinery. Moreover, diesel engines have higher thermal efficiency and save more fuel than gasoline engines. These are the advantages of diesel engines.

Components unique to diesel engines

The composition of diesel engines and gasoline engines is roughly the same. Next, some unique components of diesel engines will be explained.

1. Intercooler

Nowadays, turbocharged engines occupy a large market. Turbochargers can increase the engine intake volume so that the engine outputs more power, but using only turbochargers cannot fully exert the performance of the engine because the temperature of the gas inhaled by the turbine is often not low. However, according to the ideal gas state equation, we can conclude that lowering the temperature under the same pressure and volume can increase the quality of the gas, in other words, more gas can be inhaled. Therefore, people invented the intercooler. Before entering the cylinder, the air first enters the intercooler to complete the cooling, thereby increasing the amount of air entering the cylinder. This part was once a representative of advanced automotive technology. At that time, some high-end cars (especially trucks) would be specially marked with "turbo" (that is, turbocharged) and "intercooler" (intercooler). Initially, intercoolers were used in truck diesel engines, and now they have been widely used in turbocharged engines, whether gasoline or diesel powered.

2. High-pressure conjugate system

In diesel engines, fuel is directly injected into the cylinder, but how to improve the combustion efficiency of diesel is a problem. People have found that increasing the injection pressure can make diesel better into atomized form, thereby increasing the contact area with air and achieving the purpose of improving combustion efficiency. Therefore, high-pressure common rail systems are now widely used in diesel engines. This system can use extremely high pressure to allow diesel to enter the cylinder in atomized form to complete combustion. At the same time, "electronic injection" technology is also widely used in diesel engines today. The amount of fuel injection is precisely controlled by the program to achieve a "double harvest" of power and environmental protection.

3. In-cylinder braking and exhaust braking

When taking the driver's license test, the instructor mentioned "engine braking". This braking method is generally called "in-cylinder braking" and is widely used in diesel engines. Especially for some diesel engines with a displacement of more than 10L used in trucks, the effect of using in-cylinder braking is quite good. When in use, the engine will stop injecting fuel, but the cylinder is still running. In other words, the engine at this time becomes an oversized air compressor, which consumes energy by compressing air to achieve the effect of braking. There is also an exhaust brake, the principle of which can be understood as blocking the engine exhaust pipe, but the effect is not as good as in-cylinder braking.

4. Air compressor

Many diesel engines are used in trucks, and trucks are different from cars. A large amount of compressed air is needed for pneumatic components such as air horns and air brakes. Therefore, an air compressor will also be installed on the diesel engine to inflate the compressed air tank when the diesel engine is running. Before starting, if the barometer shows that the pressure is too low, you must put the vehicle in neutral and "warm up" on the spot to increase the air pressure, otherwise the vehicle will not be able to start.

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