A diesel engine is a type of internal combustion engine that uses diesel fuel to produce mechanical energy. Diesel engines are often used in commercial vehicles, ships and generator sets because they offer higher efficiency and higher power density compared to gasoline engines.

The operation of a diesel engine can be divided into several steps:

• Intake: In this step, air is sucked into the cylinder of the engine. This happens when the piston moves down in the cylinder, creating a vacuum that draws air into the cylinder through the open intake valve.

• Compression: After the inlet valve has been closed, the piston moves up again and compresses the sucked-in air in the cylinder. Compression causes the temperature of the air in the cylinder to increase significantly, usually to over 500 degrees Celsius.

• Injection: Shortly before the piston reaches the highest point in its movement (top dead center), diesel fuel is injected into the cylinder through the injection nozzle. The fuel is atomized into a fine mist, and due to the high temperature of the compressed air, the fuel immediately ignites and burns.

• Expansion: Combustion of fuel produces hot gases that expand rapidly and force the piston downward. This movement of the piston is converted into mechanical energy that is used to power the vehicle or other machine.

• Eject: After the piston reaches its bottom dead center, the exhaust valve opens. The piston moves up again and pushes the burned exhaust gases out of the cylinder and into the exhaust system.

Diesel engines do not use spark plugs to ignite fuel, instead relying on the high temperature of compressed air to self-ignite the fuel. This distinguishes them from gasoline engines, which require a spark to ignite the fuel-air mixture.

Another difference is that diesel engines generally have a higher compression ratio than gasoline engines, resulting in better fuel efficiency and performance. However, because diesel engines generate higher pressures and temperatures in the cylinder, they must be built stronger and heavier to withstand these loads.