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Business 459 views Sep 11, 2017
How Does a Diesel Engine Work?

In the past, diesel engines were unreliable, smelly and noisy, primarily used for only trucks and vans. But with time, new technologies like Garret Turbo and Donaldson filters were developed. Today, diesel engines have become highly efficient and reliable, resulting in better performance and lower vehicle ownership costs.

A diesel engine has the same components as a petrol engine and uses the four stroke cycle, but works in a different manner. Considering a petrol engine, a spark ignites the mixture of fuel and air. A diesel engine achieves ignition just by compressing the air. The compression ratio, in this case, is around 20:1, whereas it is only 9:1 for a petrol version. Since the compression ratio is high, air is heated to high temperatures to ignite the fuel, without requiring a spark. Thus, this means that a diesel engine has no separate ignition system.

The amount of air that a petrol engine sucks depends on the throttle opening. This opening can be made large or small, so variable amounts of air are drawn in. A diesel engine sucks in air in the same amount at every engine speed through an inlet tract which is operated by a separate inlet valve; a diesel engine doesn’t have a carburetor or a butterfly valve. This inlet valve shuts off when the piston arrives at the induction stroke’s effective end. The piston reaches the cylinder top and compresses air to 1/20 of its initial volume. A measured quantity of diesel is injected into the combustion chamber. The compressed air produces heat which ignites the mixture of fuel and air. The piston is forced back downwards, and the crankshaft is turned in the process.

The piston then moves up the exhaust stroke cylinder, which opens the exhaust valve. The burned and expanded gas is then passed on to the exhaust pipe. Once the exhaust stroke ends, the cylinder can be charged through another cycle.


The primary components of a diesel engine are the same as a petrol engine and perform the same functions. However, they are built stronger because diesel engines bear higher loads. The walls are much thicker, provide greater strength and absorb shock better. Plus, the heavy duty block reduces noise to a greater extent than a petrol engine.

Like all other components, the pistons, bearing caps, crankshafts and Donaldson filters are all stronger. The head of the cylinder is different because of a different combustion mechanism.


An internal combustion engine operates well only when air and fuel are mixed well. In a diesel engine, both of these are injected at different instances in the cylinder, and so must be mixed inside. Injection is either direct or indirect.

Indirect injection introduces turbulence, which is one of the simplest ways of mixing the injected fuel with compressed air. Fuel is squirted in a swirl chamber and then injected into the combustion chamber so that it can mix well. Considering direct injection, there is no swirl chamber and the fuel is directly injected into the combustion chamber, where turbulence is created by the piston crown.