Diesel Engines

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Most modern diesel engines use conventional cylinders and piston installations that work with slider crank mechanisms that are shared with other internal combustion engines such as gasoline engines. Given this basic mechanism, the basic structure of a diesel engine and a gasoline engine has little difference.

Conceptually, a diesel engine operates by compressing air to high pressure / high temperature and then injecting a small amount of fuel into hot compressed air. At high temperature, a small amount of atomized injected fuel evaporates. Mixed with the high temperature ambient air in the combustion chamber, the evaporated fuel reaches its autoignition temperature and burns to release the energy stored in the fuel [391].

The definition of diesel engines has evolved over the years. For example, at the beginning of the 20th century, the "actual diesel engine" was different from certain aspects of the diesel cycle, but it did not cover all aspects considered part of the diesel cycle. The initial definition of "real diesel engine" is characterized by the following features [2959].

The maximum cycle pressure (achieved during combustion) does not exceed the compression pressure significantly. That is, there is no big explosion effect.

The first point of the above function is consistent with modern diesel engines, but the latter two do not match. In the 1920s and 1930s, the other two functions lost their meaning.

Solid fuel injection began to appear around 1910, but it was not immediately recognized until the late 1920s. It is noteworthy that diesel's own air jet selection is more necessary than choice. Diesel envisages a solid injection fuel system rather than an air injection system

Diesel is very strict to stick to constant pressure combustion, but this can only be achieved with a large, relatively slow diesel engine that was common before the 1920's. For smaller smaller high-speed engines that appeared in the 1920s, a practical consideration implied that combustion was close to constant volume processes such as Otto cycle rather than constant pressure within diesel cycles.

In 1897, when the first diesel engine was completed, Adolphus Busch visited Cologne and negotiated an exclusive right to produce diesel engines in the US and Canada. In his engine test, it was noted that the diesel engine at that time was operating at 27% thermodynamic efficiency, but a typical expanded steam engine would be operated at about 7 to 10% speed It was. In the early 20th century when large diesel engines were used for the first time, the engine at that time was of the same type as the conventional composite steam engine, and the piston was connected to the connecting rod via cross head bearing. After steam engine practice, some manufacturers burned on both sides of the piston using two sets of valve gears and fuel injection and built a double acting two-stroke and four-stroke diesel engine to increase output

For two reasons, the naturally aspirated diesel engine is heavier than the same output gasoline engine. First of all, in order to obtain the same output as the gasoline engine, a larger displacement diesel engine is required. This is mainly because diesel engines must operate at lower engine speeds. Since diesel fuel is injected before ignition, the fuel has little time to find all the oxygen in the cylinder. In a gasoline engine, air and fuel are mixed throughout the compression stroke to ensure complete mixing even at higher engine speeds. The second reason for the greater weight of the diesel engine is that it must be stronger to withstand the higher combustion pressure required for ignition and the impact load from the explosion of the ignition mixture.

In a place where the diesel engine and gas engine are different, the fuel is ignited inside the engine. In gas engines, air and fuel are compressed, and the spark plug ignites the mixture at important points in cycle timing. However, in a diesel engine, there is no spark plug. When the diesel fuel and air are throttled down completely, enough heat is generated to burn the mixture naturally due to extreme compression. This is called "compression ignition" and is the basis of the principle of operation of diesel engines. When the gasoline engine has compression ignition, we often call it "knocking" to destroy the engine. However, the diesel engine was made to use it.