Diesel Engines: Definition, Parts, Working, Types, Applications

In this article, we will learn all about diesel engines along with definition, invention, parts, working procedure, advantages, disadvantages, applications, etc.

Let’s explore!

What are Diesel Engines? Definition, Invention

Diesel Engines Definition

The diesel engine is an internal combustion engine that compresses the air into the cylinder to produce heat used to ignite the fuel. The chemical energy stored in power is converted to mechanical energy, used to run the engines.

  • They are also called compression-ignition technology since combustion depends on air heated by compression and not electric spark.
  • Most modern diesel engines operate on piston, cylinder, and slider-crank mechanisms, the basic arrangement of all internal combustion engines.
  • It needed more time to become commercially successful.

In 1913, Diesel died. His parents started to expire. Later on, the design of Rudolf’s diesel engine was taken over by large companies for further development.

Who invented diesel engines

It was named after its German inventor and thermal engineer Rudolf Diesel. It was remodeled in 1893 and operated on peanut oil.

  • Diesel proposed a design to increase the efficiency of the Otto engine (the first four-stroke cycle engine of the 19th century invented by Nikolaus Otto).
  • Rudolf said that the spark ignition process could be replaced by compression through a piston- cylinder.
  • He explained that compression could heat the air to a temperature higher than the given fuel’s auto-ignition temperature.

He worked on this design and proposed a cycle in 1892-93. During his invention, steam engines were very popular, especially in industries.

Diesel Engine Concept

A diesel engine is also termed an intermittent combustion piston-cylinder device. The process of combustion varies between a gasoline engine and a diesel engine.

  • A gasoline engine ignites an electric spark by burning gasoline or gasoline mixture like ethanol, producing power.
  • The process of combustion is homogenous.
  • On the contrary, a diesel engine compresses the air by a piston and injects the fuel into the chamber at the end of the compression stroke. So, the combustion process is heterogeneous.

Parts of Diesel Engines

Following are the major and distinctive parts of a diesel engine:

Fuel system

The fuel reaches the cylinder bore by following a pathway. The path comprises a fuel tank, water separator, feed pump, filter, injection, pump, injector nozzle, and cylinder from the start until the end.

  • Fuel tank stores the fuel. It is made up of sheet metal.
  • It constitutes a fuel gauge (for checking fuel level) and a drain plug (for draining fuel).
  • The water separator separates impurities and water from fuel.
  • As the name indicates, the feed pump feeds fuel into the filter and injection pump.
  • In the fuel system, pressure is exerted on fuel such that it opens the nozzle and moves the fuel to the chamber.
  • The injection pump performs the function.
  • The pressure ranges between 350 and 450 psi.
  • The injector nozzle firstly achieves atomization, which is the breakdown of fuel into small particles.
  • The force required for this process is 1500 to 4000 psi. After that, it moves it into the chamber.

Oil/lubrication system

It uses oil under pressure to overcome friction hence preventing the engine parts from wear and tear.

  • The oil system comprises oil pumps and filters to the oil clean from impurities.
  • The lubrication system aids in the removal of foreign particles, removes heat from engine components, overcomes friction, and prevents the seizure of rubbing surfaces.

Cooling system

It functions to reduce the temperature of oil used for lubrication and sustain the normal functioning of the engine.

  • Higher temperatures are known to decrease the viscosity of the oil.
  • It can lead to the formation of a layer between engine parts which is harmful.
  • The cooling system has a coolant that prevents corrosion.
  • In some engines, there is a coolant filter and a coolant pump.
  • The coolant pump circulates the coolant around the area to be cooled (a regulator or sometimes heat exchanger).

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Exhaust system

Combustion results in the production of exhaust gases that are emitted into the atmosphere.

  • These gases enter the cylinder and pass on to the exhaust valve, exhaust port, exhaust manifold, turbocharger, and muffler.
  • If these gases were directly discharged to the outside, they would produce a loud sound because their pressure is higher than the atmosphere.
  • Exhaust systems overcome this problem.
  • The muffler, at the end of the system, dampens the emissions and noise.

Air-intake system

It comprises several parts; air cleaner, turbocharger, intake manifold, an inlet port, inlet valve, cylinder bore.

  • Air cleaner prevents the dust particles from entering into the cylinder bore.
  • Heavy diesel engines have a filter set containing many safety filters and outer filters for effective filtration.
  • The air sucked up by the air filter is first compressed before entering into the cylinder bore.
  • This function is carried out by turbocharger. It is an important part because it increases engine efficiency.

The pipe that transports air from the turbocharger to the inlet port is called a manifold. Inlet valve passes on-air to the cylinder bore. The camshaft carries out the opening and closing of the valve.

Electrical system

The starter motor, alternator, and battery make up the electrical system. The battery provides power to the starter motor, which rotates the flywheel (pinion in an engine is engaged with a flywheel in this process).

  • It causes rotation of the crankshaft aftermath.
  • It results in the movement of pistons and cylinders.
  • Pistons suck air and fuel, transfer them to the combustion chamber; hence engine starts.
  • Motor withdraws pinion when the engine has reached a specific rpm. Alternators act as a charger for the battery.

How Do Diesel Engines Work?

Working Principle of Diesel Engine

Let’s see the working principle of diesel engine,

  • The pistons inside the engine compress the air with pressure along with the diesel fuel. 
  • As a result, the mixture blows up and pushes the piston back at its initial position creating a reciprocating motion. 
  • The crankshaft converts it into rotatory motion. 
  • It is the process that converts the chemical energy into mechanical energy used for running the engine. 
  • Compression ratios of these engines range from 14:1 to 22:1.

Working Process of Diesel Engine

Let’s see how do diesel engines work in step by step.

  • Start the engine with the ignition key.
  • It will inject pressurized fuels into the cylinder. This pressure will heat the inner air of the cylinder and warm the things in seconds. If the combustion engines are already heated, it’s easy to start the engine.
  • Glow plugs are used by manufacturers to heat the inner air of cylinders. Although highly pressurized fuel injections produce enough hear still glow plugs are used for emission control. They help in the generation of more heat and efficient burning of fuel.
  • After the start-up of the engine, fuel is distributed to the engine with the help of a fuel pump.
  • The fuel passes through many filters which makes it clean from impurities and other contamination. Otherwise, it will become a hindrance in tiny holes of injector nozzles.
  • Now the pressurized fuel is pumped into a delivery tube which is also known as rail. This tube can contain the fuel with constant pressure.
  • It releases the fuel to the required cylinders at the proper time. Fuel injectors are used to spray the fuel in the cylinder chamber with the help of a nozzle. It helps in maintaining the fuel pressure as well.
  • Hydraulics, crystalline wafers, and other spray system are also used for fuel injection. Fuel blends with air and heat in a cylinder. It leads to a fiery power play in the cylinder.
  • Air comes through an air cleaner or turbocharges. Modern turbocharges can increase power production with low fuel consumption.

Types of Diesel Engines

Based on Operation

Based on the operation, diesel engines can either be four-stroke cycle engines or two-stroke cycle engines. Their function and construction are discussed below:

Four-stroke cycle engine

This engine has a dual valve arrangement i.e. It has two intakes valves and two exhaust valves. Along with these valves, the nozzle for injecting fuel is all located in the chamber.

Two-stroke cycle engine

This engine is constructed smartly as compared to a four-stroke engine. For the cleaning and intake of air, ports are present on the lining of the cylinder.

Exhaust occurs either through these ports or through the valves located in the cylinder head. Engine based on port design is simpler as compared to the one containing exhaust valves.

Based on Size

There are three types of diesel engines; small, medium, and large. This categorization, along with size, is also based upon their power and application.

Small engines

Their power is approximately 188 kilowatts (252 horsepower). They are most common and produced in large numbers. They apply to automobiles, light trucks, some agricultural machinery, construction machinery, and small electrical power generators that are stationary. They are mostly turbocharged, containing after-coolers. Their construction is such that they are in-line, include four or six cylinders, and are direct injection engines. You can find these types of diesel engines for saleOpens in a new tab. in common trucks like the Dodge Ram 2500, Chevrolet Silverado 2500 HD, etc.

Medium engines

The power ranges from 188 to 750 kilowatts (252-1006 horsepower). Heavy-duty trucks have medium-sized engines. They are in-line, turbocharged, direct injection, having six cylinders and after-coolers. This category includes some V-8 and V-12 engines also.

Large engines

Their power is up to 750 kilowatts or above. They are used for locomotives, marine, generation of electrical power, etc. They are after-cooled, turbocharged, and direct injection engines. In cases of critical durability, they can work for as low as 500 revolutions/minute.

Apart from these types discussed above, there are many other types based upon,

  • cylinder bores,
  • pistons and rods,
  • cylinder arrangement, and
  • engine speeds.

Based on Type of Fuel Injection

Diesel engines are classified into direct injection (DI) and Indirect Injection (IDI), based on the type of fuel injection.

Direct Injection

The surfaces of pistons and cylinder head completely close the combustion chamber such that it resembles a cavity or bowl in the piston crown.

Indirect Injection

The combustion chamber has two parts: a cavity (different from the one found in DI), and the second part constitutes a pre-chamber. One or two pathways connect the pre-chamber to a cylinder. The fuel is inserted into the pre-chamber.

IDI systems belong to the 80s and 90s, whereas DI systems are advanced and used in most vehicles.

  • Comparing both, DI has higher thermal efficiency, greater atomization due to more holes on the injection nozzle is easier to start in cold weather, and has higher injection pressure than IDI technology.
  • The compression ratio for Indirect Injection is higher.
  • The fuel consumption is less due to low thermal efficiency.
  • There are few demerits of DI too.
  • They are louder, more susceptible to blockages due to small injection pores, lower power output, and at lower speeds, slow air swirling.

Advantages of Diesel Engines

Following are the advantages of diesel engine:


As compared to gasoline engines, diesel engines are far more efficient. Their framework is such that it produces more usable energy for engine functioning. Turbochargers and after-coolers also play a vital role in increasing the efficiency and power of the engine.


Diesel engines have high mileage and are 25-30% more efficient and economical than the same gasoline engine operating. Fuel cost is 30 to 50% lower than gas engines.

No tune-ups

Ignition tune-ups are not required due to a diesel engine’s lack of spark plugs and distributors.


They resist high compressions and work much longer before a repair is needed. This property increases durability and longevity.


They are faster than a gasoline engine. It provides more torque to the driveshaft (transfers torque to wheels from vehicle engines) for burning fuel, making them swift and more productive.

Thermal Efficiency

Higher pressure in cylinders and higher temperature results in greater thermal efficiency.

Environmental advantage

They use excessive air in cylinders, which reduces hydrocarbon and particulate matter in exhaust gases released outside. Modern diesel-based engines have low CO2 and pollutants emissions.

No sparking

There are no spark plugs and wires due to auto-ignition. It results in no sparking and lower maintenance expenses.


Gas units burn hotter; hence diesel units have a comparatively longer life.


They come in two variants; air-cooled and liquid-cooled engines. Liquid-cooled engines are favored more since they efficiently control temperature and are much quieter.


Due to high density, diesel fuels can attain more energy than gasoline.


Diesel has amazing lubrication properties.

No-fire hazards

The risk of catching fire is lower because it does not produce flammable vapor.


It is an electrically heated wire that produces extra heat, beneficial in cold regions and the winter season. They are commonly found in small diesel engines.

Effective Operation

Before any maintenance is required, water-cooled diesel engines operate for about 12,000-30,000 hours at 1800 pm. It is cost-friendly and reliable.

Common rail fuel systems

Recent engines come with an additional feature of common rail fuel systems to limit noise and exhaust emissions to a larger extent resulting in a good performance.

Disadvantages of Diesel Engines

Despite numerous advantages, diesel engines have some drawbacks that are discussed below:

  • Diesel engines need regular maintenance to work properly. Many vehicles have water separators that must be emptied and cleaned.
  • If the maintenance is ignored, it will cause damages that will cost you more money. Based on advanced technology, such repairs in a diesel engine are more costly than gasoline engines.
  • Once they used to be cheaper than gasoline, but due to their greater consumption, the prices are high now and will continue to rise in the future also.
  • Due to combustion in diesel engines, they are sometimes considered a bit slower than vehicles powered by gas. Gas-powered machines are fast and fiery, whereas diesel engines are slow, efficient, and durable.
  • If not tuned properly, diesel engines will produce a lot of noise and smoke.
  • Diesel-based car engines are costly. They sometimes operate on fuel sources that are hard to find. Moreover, they become less efficient in city driving.
  • Diesel exhaust is a carcinogen that increases the risk of lung and bladder cancer.
  • Fuel must have a proper viscosity; otherwise, the fuel line and injection pump can get damaged.

Applications of Diesel Engines

World War I and II

Diesel engines were used during World War I for submarines and proved to be reliable during wartime. They were also used as main power sources in military equipment (ground and sea) during World War II.

Since then, they have been used extensively in many areas all over the globe.

Diesel-powered Generators

They have widespread use in marine, locomotive, telecommunication, hospital, airports, agriculture, forestry, mining, industries, and construction. They are very useful power sources.

On a low scale, single-phase diesel-powered generators are used at homes. On a larger scale, three-phase generators are used in industrial and commercial areas.

Stationary diesel engines

They are used for electricity production.

Highway and construction equipment

This is considered the best choice for construction and highway machinery like bulldozers and front loaders.

Farming equipment

Due to their durability, they are widely used in farming equipment or vehicles such as tractors.

Truck and bus applications

Heavy-duty trucks and buses are fitted with a diesel engines.

Marine vehicles

Ships, cargos, and boats significantly use these engines since they are economical and easy to operate for large marine vehicles.


Freight trains carry huge loads. A powerful and efficient engine is required for its functioning, and diesel engines are the top choice.

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Diesel engines are very reliable and cost-effective among all types of internal combustion engines. They have several characteristics that make them a leading technology. They have certainly replaced gasoline engines. With the development in science and technology, it is constantly being improved to overcome a few drawbacks.

Their efficiency is high due to the high ratio of compression. They offer combustion for a huge variety of fuels. Their exhaust emission system is impressive. Compared to the early Otto engine, emission of pollutants, including carbon dioxide, is about ten times lesser.

They easily adapt to damp environments since they are not based on an electrical-ignition system. Instead, their function is based on a fuel injection system. Petrol engines can wear and tear due to high pressure, but this is not the case for diesel engines.

Diesel clatter, the noise produced in the engine due to ignition, is irritating, but it has been overcome through indirect injection methods. In the past, the fuels included petrol, kerosene, gas oil, vegetable oil, mineral oil, or mixtures of these oils.

Later, diesel was considered the standard fuel to be used in diesel engines. Direct injection engines are more satisfactory as compared to indirect injection engines. Instead of fuel injection, carburetion was used in gasoline engines resulting in a reduced compression ratio.

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One thought on “Diesel Engines: Definition, Parts, Working, Types, Applications

  1. I like that you mentioned how diesel engines are far more efficient as compared to gasoline engines. I was checking out some automotive engines earlier and I learned quite a bit about how diesel engines work. From what I’ve read, it seems diesel engine spare parts are easy to get now too.


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