What is Diesel Combustion?

Jason C. Chavis

Diesel combustion uses the thermal energy created from the compression of air and fuel to create an ignition. This ignition leads to the burning of fuel injected within a combustion chamber of the engine. It differs from gasoline combustion, which uses combustion of air and fuel ignited by a spark plug. A diesel engine operates on either a two-stroke or four-stroke method and uses a fuel refined from petroleum, biomass, oil waste or other sources.

Diesel fuel is ignited to create energy.
Diesel fuel is ignited to create energy.

The air and fuel mixture is very important to making diesel combustion work efficiently. Air is compressed into a combustion chamber with approximately a 600 pounds per square inch (about 40 bar) pressure. Due to the sheer compression, the air within the chamber heats up to approximately 1000°F (roughly 550°C).

Inhaling exhaust fumes expelled from a diesel engine may cause breathing difficulties.
Inhaling exhaust fumes expelled from a diesel engine may cause breathing difficulties.

Diesel fuel is then pushed into the chamber with the compressed air using a fuel injector. The injector itself breaks down the fuel into tiny droplets, ensuring it is evenly distributed throughout the chamber. The heat vaporizes the droplets, causing combustion and the pressure pushes the piston outward, powering the crankshaft. This gives the diesel engine its typical “knocking” sound.

The benefit of diesel compression is the fact that the system operates without a separate ignition system, as is the case in gasoline engines. The level of compression can be increased within a diesel engine in order to increase fuel efficiency. This can occur without the threat of damage to the cylinder. In addition, the fact that only air is compressed before fuel is introduced means that there is no threat of premature detonation, again damaging the engine.

The diesel engine was invented in the late 1800s. Having a love for engine design, refrigerator engineer Rudolf Diesel began exploring the concept of the internal combustion engine in the late 1880s. Diesel developed the first engine that operated without a spark, and filed for a patent in 1894. Within three years, he successfully demonstrated the power and efficiency of diesel combustion. The patent was approved in 1898.

Diesel's discovery and subsequent invention was the first to deal with the laws of thermodynamics in an internal combustion engine. Diesel combustion uses the natural physical process of heat transference that was a very creative manner for the time period. In addition, the inventor had an overall sociological intent: Diesel wanted the engine to help independent industry to be able to compete with larger businesses.

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