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An Overview of the Diesel Engine

Yogesh Ambekar
A diesel engine is an internal combustion engine, in which fuel is ignited by high temperature and high pressure gas, rather than a separate source of energy like a spark plug. The invention of this magnificent contraption was done in 1893 by Rudolf Diesel.
Rudolf Diesel was born in the year 1858 in Paris. His love for his work could be inferred from an incident involving an explosion of an engine which almost took his life but did not deter him from his work. His engine was the first that provided evidence that fuel could be ignited without a spark.

Types of Diesel Engine

Diesel engines can be broadly distinguished as two-stroke and four-stroke. Bulky engines usually operate on the two-stroke cycle. Lighter engines generally operate on the four-stroke cycle.
Generally, cylinders are used in multiples of 2, 4, 6, or 8. It doesn't matter what number of cylinders are being used as long as the load on the crankshaft is counterbalanced to prevent excessive vibration. The inline-6 cylinder is used widely in medium and heavy duty engines.

Working of the Diesel Engine

The temperature of gas rises when it is compressed. When the inlet valve opens, air is sucked into its cylinder due to the vacuum created. The piston then moves upward and compresses air, raising its pressure and temperature.
As the piston moves up towards the end of the compression stroke, diesel is injected into the combustion chamber, compressing the air, which in effect also facilitates combustion in the cylinder.
There is high pressure inside the cylinder, so the fuel is injected through an atomizing nozzle at reasonably high pressure. The mixture of fuel and air then ignites and burns rapidly. The gas in the chamber expands. This forces the piston to move down, thereby producing power stroke.
The connecting rod which is linked to the crankshaft forces it to turn and delivers rotary power at the output end of the crankshaft. Scavenging of the engine is completed either by ports or valves.

Accessories of a Diesel Engine

Turbocharger is a vital accessory, and is used to compress the input air. It is a supercharger with superior efficiency, to supplement the air in the chamber and for its rapid compression. To increase the efficiency, an after cooler/intercooler is used to cool the air after compression.
The speed of the engine can be controlled using Governor by adjusting the rate of fuel delivery. In cold weather conditions, these engines can prove problematic. To overcome this problem, a small electric heater called a glow plug is used inside the cylinder to warm the cylinders prior to starting.
You can also have resistive grid heaters in the intake manifold, to warm the inlet air until the engine reaches operating temperature. Engine heaters fixed into the utility grid are mostly used when an engine is shutdown shut down for long period periods in cold weather to lessen the startup start-up time and engine wear.

Comparison with Diesel Engine

It is more efficient than a gasoline engine as they have it has a comparatively high compression ratio. The limitation of a gasoline engine is that it cannot be used for heavy duty applications, as the components cannot withstand the stress caused on them. Diesel engines have a longer life.
For the same power produced, diesel engines are heavier compared to petrol engines. It causes more pollution as compared to gasoline engines which are eco-friendly. When compared on cost basis, they prove to be more expensive. The noise and vibration produced by diesel engines makes them less popular.


The diesel engines used today are more superior to Rudolf Diesel's original concept, since a lot of new developments have been done. They are used in trucks, ships, submarines, locomotives, and in electric generating plants. Most of the modern heavy road vehicles, large-scale portable power generators, and most farm and mining vehicles have diesel engines.
It continues to be most the economical thermal engine till date. Even today, this equipment is the first choice of any person looking at the difference in price and efficiency, compared to gasoline. A lot of research work is going on to improve the efficiency and reduce pollutants.
The new diesel engine designs have advanced computer control controls that eliminate many of these disadvantages, like noise, smoke, vibration, and high cost. In the coming years, we are likely to see many more diesel engine enabled vehicles on the road.