Like a gasoline engine, a diesel engine is a type of internal combustion engine. Combustion is another word for burning, and internal means inside, so an internal combustion engine is simply one where the fuel is burned inside the main part of the engine (the cylinders) where power is produced. The basic difference between a diesel engine and a gasoline engine is that in a diesel engine, the fuel is sprayed into the combustion chambers through fuel injector nozzles just when the air in each chamber has been placed under such great pressure that it’s hot enough to ignite the fuel spontaneously. The temperature of the air inside the combustion chamber rises to above 400°c to 800°c. This, in turn, ignites the diesel injected into the combustion chamber. Thus, the ‘Diesel Cycle’ does not use an external mechanism such as a spark-plug to ignite the air-fuel mixture.
Basically, there are two types of diesel engines which are Four Stroke and Two Stroke types. The ‘Diesel Cycle’ is also known as Compression-Ignition Cycle and uses higher Compression-Ratio. It was named after German engineer Rudolph Diesel, who invented and developed first Four-Stroke diesel engine. Although the four strokes of the diesel engine are similar to that of a petrol engine, the ‘Diesel Cycle’ considerably defers by the way the diesel is supplied to the engine and the method by which it is ignited.
The Four-Stroke diesel engine works on the following cycle:
- Suction Stroke –With pistons moving downwards and opening of the inlet valve creates suction of clean air into the cylinders.
- Compression Stroke –With closing of Inlet valve the area above the piston gets closed. The piston moves up resulting in compression of the air in a confined space under higher compression-ratio.
Combustion Process – At this stage the injector sprays the diesel into the combustion chamber. The rise in temperature of the air caused by its compression; results in instantaneous burning of diesel with in an explosion. This causes heat to release which generates expanding forces known as power.
3. Power Stroke – These forces again push the pistons downwards resulting in their reciprocating motion.
4. Exhaust Stroke – On their way up, the pistons push the exhaust gases above them thru’ the exhaust valve which opens during exhaust stroke. This cycle repeats itself until the engine turns off, resulting in continuance of engine’s running.
Advantages and disadvantages of diesel engines
Diesels are the most versatile fuel-burning engines in common use today, found in everything from trains and cranes to bulldozers and submarines. Compared to gasoline engines, they’re simpler, more efficient, and more economical. They’re also safer, because diesel fuel is less volatile and its vapor less explosive than gasoline. Unlike gasoline engines, they’re particularly good for moving large loads at low speeds.
Pollution is one of the biggest drawbacks of diesel engines: they’re noisy and they produce a lot of unburned soot particles, which are dirty and hazardous to health. In theory, diesels are more efficient, so they should use less fuel, produce fewer carbon dioxide emissions, and contribute less to global warming.
Read Also: Petrol Engine Principle and Working Cycle
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