Diesel Engine Principle and Working Cycle Explained:
Diesel Engine Cycle:
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.
A conventional internal combustion diesel engine works on 'Diesel Cycle'. In the simple diesel engines, an injector injects diesel into the combustion chamber above the piston directly. Diesel engines are also commonly known as Compression-Ignition engines; since the diesel is burned due to hot compressed air. The temperature of the air inside the combustion chamber rises to above 400°c to 800°c, which in turn, ignites the diesel which was injected into the combustion chamber. The 'Diesel Cycle' does not use an external mechanism such as a spark-plug to ignite the air-fuel mixture.
The Four-Stroke diesel engine works on the following cycle:
1. Suction Stroke – With pistons moving downwards and opening of the inlet valve creates suction of clean air into the cylinders.
2. 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 resulting in generation of 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 is turned off, resulting in continuance of engine’s running.
A diesel engine is mainly classified into two types - Indirect-Injection (IDI) & Direct-injection (DI). The Direct-Injection diesel engine is an earlier generation technology which later evolved into its successor & more advanced CRDi. Today, simple DI engines are still being widely used, especially in utility vehicles, trucks, buses & generators. The more sophisticated & refined CRDi diesel engines have also become very popular in the Sedans, MPVs, SUVs and Luxury cars in the recent past.