How Does a Diesel Engine Work?

Internal combustion (IC) engines are most commonly used in different vehicles. These are the most efficient and high-performance engines. IC engines have multiple types, and a diesel engine is one of them. A diesel engine is also known as a compression ignition (CI) engine.

In this engine, the compression process occurs due to the high compression of air. This article properly explains the diesel engine working, types, and applications.

What is a Diesel Engine?

An engine in which diesel fuel is ignited due to high compression of air in the combustion chamber is known as a diesel engine. A diesel engine is also known as a compression ignition engine because, in this engine, ignition occurs due to the high compression of air.

In this engine, there is no use of a spark plug for ignition. In 1893, Rudolph Diesel invented the first diesel engine.

A diesel engine has more efficiency than other internal combustion engines (i.e., gasoline engines). This is because it has the highest inherent lean burn and expansion ratio, which makes the heat to be dissipated by the excess air.

In 1910, these engines were used for ships and submarines. After some time, they have been used in applications like electricity-making power plants, agricultural equipment, heavy apparatus, trucks, and locomotives.

These types of engines are famous because of their longevity and durability. Diesel engines also have the ability to generate high levels of torque, which makes them suitable for use in heavy-duty vehicles.

How Does a Diesel Engine Work

History of Diesel Engine

Rudolf Diesel invented 1st diesel engine in 1878. He was a student at Polytechnikum in Munich. The diesel engine is named based on the name of Rudolf Diesel.

After working for many years, Diesel published his ideas about the diesel engine in 1893 in the essay “Theory and Construction of a Rational Heat Motor.”

 Diesel engine built by Langen & Wolf under license, 1898

Diesel used oils such as vegetable oils to invent his first engine as he had no formula for diesel infrastructure at that time. The very high compression ratio was used to generate the high pressure and high temperature required for automatic combustion. It was the main feature of the compression ignition engine.

A method of injecting fuel directly into the combustion chamber was also required. Over time, the infrastructure of oil pollution became fuel such as gasoline (to support gasoline engines), petroleum and fuel oil (boiler room), and diesel oil.

How do diesel engines work?

Diesel engines utilize four-stroke combustion cycle to convert chemical energy available in diesel fuel into mechanical energy. This mechanical power moves the pistons up and down (pistons are designed inside the cylinder).

Hence, the crankshafts connected with pistons move up and down accordingly. This motion is known as the linear motion, which helps create the rotary motion in order to turn the wheel of machinery forward.

Diesel engine cycle

For a diesel engine, the cycle in an internal combustion engine consists of induction, compression, combustion and exhaust strokes. The air is first compressed, and then the diesel fuel is injected. Air heats up when it is compressed. Finally, the diesel fuel ignites.

The four strokes:

  • Intake: Inlet opens, drawing air into the cylinder and moving the piston down.
  • Compression: Inlet closes, the piston is driven upwards in the cylinder and compresses the air.
  • Combustion: Diesel fuel is injected into the cylinder before the piston reaches to the top. Fuel is ignited and force the piston downwards.
  • Exhaust: The piston moves downward and reaches to the top, which pushes the exhaust created by the combustion out through the exhaust valve.

Read also: Petrol Engine Working

Diesel Engine Parts

There are several systems in a diesel engine and each must work correctly to power it. Below is a breakdown of some of the most important components of a diesel engine.

Fuel system

The fuel system consists of the fuel tank, water separator, feed pump (low-pressure), filter, high-pressure pump, injector nozzle and cylinder.

Essentially, the fuel tank stores the fuel, then a low-pressure pump pulls the fuel from the tank through a filter/water separator, then pushes the fuel through another filter.

From there, fuel pressure is stepped up via a high-pressure pump, whether it is an injection pump or a unit injector.

Lubrication system

The lubrication system plays an important role in the engine. It reduces wear and tear of rubbing surfaces by placing a film of oil between parts, reduces the power required to overcome friction, and removes heat from the pistons and other parts in the engine. It also separates the cylinders and piston rings.

Air intake system

Ever wondered, “How does a turbo work in a diesel engine?” In this system, air flows into the cylinder bore through the air cleaner, which prevents dust from entering. The turbocharger compresses air from the air filter, and the intake manifold takes the air from the turbocharger to the inlet port.

Finally, the intake valve allows air to pass into the cylinder bore, and a camshaft controls when the valve opens and closes.

Exhaust system

In this system, exhaust gas is passed through the diesel particulate filter, which traps solids in the exhaust stream. These solids, or particulates, are carbon and ash.

The filter will need to undergo a cleaning process called regeneration periodically to convert the carbon into carbon dioxide through exposure to high temperatures.

The gas then passes through the selective catalyst reduction system, which removes the oxides of nitrogen with the help of diesel exhaust fluid. There is also an exhaust gas recirculation valve, cooler and mixer in this system. All of this equipment is there to reduce harmful emissions.

Cooling system

The cooling system helps maintain proper engine temperature, which allows all of the parts to work correctly. It keeps oil and engine components at the right temperature, which in turn helps protect the cylinder head, cylinders, valves and pistons.

There are two different types of cooling used in internal combustion engines: air cooling and water cooling. While gas engines can use either method, diesel engines use water cooling exclusively.

Electrical system

The electrical system is made up of the alternator, starter motor and battery. The starter motor, which is powered by the battery, rotates the flywheel, which rotates the crankshaft. This is what causes the pistons to move in the cylinders.

The piston compresses the air in the cylinder to create heat, which ignites fuel injected into the cylinder.

Diesel Engine Efficiency

A diesel engine has high efficiency because of its high compression ratio. The lack of a throttle valve means very little air exchange loss, which consumes less fuel, particularly at medium and low loads. Due to these reasons, diesel engines are very economical.

According to Rudolf Diesel, the actual productivity of a diesel engine should be from 43.2% to 50.4% or more.

The actual efficiency of a diesel engine in the latest passenger cars can reach 43%, while engines in heavy diesel buses and trucks reach maximum efficiency of up to 45%. But, the driving cycle has less average efficiency than the maximum efficiency.

The maximum efficiency of a diesel engine is about 55%, which can achieve with a large 2-stroke marine diesel engine.

Types of Diesel Engines

The diesel engine has two major types that are:

  1. 4-stroke diesel engine
  2. 2-stroke diesel engine

#1. 2-Stroke Diesel Engine.

The 2-stroke diesel engine is a type of compression ignition engine that completes a power cycle in only two strokes of the piston.  It ignites the fuel due to the high compression of air. 

Advantages and disadvantages of Two-stroke Diesel Engine: –

AdvantagesDisadvantages
They have a low weight.The two-stroke diesel engine has unstable idling.
They have low cost.These engines produce high pollution.
These engines can work in any position.They have high noise.
These IC engines are easy to start.They have high vibrations.
They have a simple mechanism.These have scavenging issues.
They require low maintenance costs.Low volumetric and thermal efficiency.

Read more: Two-stroke Engine working

2) 4-Stroke Diesel Engine

It completes a power cycle after two revolutions of the crankshaft or four strokes of the piston. You can find these engines in heavy vehicles like buses, coaches, tractors, cars, etc.

Advantages and disadvantages of 4-stroke Diesel Engine: –

AdvantagesDisadvantages
This diesel engine has a high cost.This diesel engine has high cost.
It has a high compression ratio.They have a complex design.
They generate less pollution.They are less powerful than a two-stroke engine.
They have high durability.These engines have more parts.
They have high fuel efficiency.They have a high weight.

Read more: Four-stroke Engine working

Difference between Diesel Engine and Gasoline Engine

Diesel EngineGasoline Engine
A diesel engine operates on the diesel cycle.A gasoline engine operates on the Otto cycle.
It is more efficient.It is less efficient.
They are depleted in heavy-duty automobiles like buses, tractors, cars, etc.They are most commonly depleted in small vehicles like vans and bikes etc. 
These are very expensive.They have a low cost.
A diesel engine uses diesel which is very expensive.A gasoline engine uses petrol or natural gas which is less expensive.
It has a high compression ratio.It has a relatively low compression ratio.
These have high maintenance and initial costs.These engines have low maintenance and initial costs.
Diesel fuel is more difficult to ignite.The gasoline fuel is easy to ignite.
It produces high noise while working.It produces less noise.
A diesel engine has low fuel consumption.A gasoline engine has higher fuel consumption.

Advantages of Diesel Engines

  • It doesn’t require a spark plug for combustion.
  • A diesel engine has high efficiency than a SI engine.
  • It has high speed. 
  • It uses a smoke trap to improve the torque. If only a reduction of SW and protection is in operation, the pumping and pumping capacity can be reduced, and the capacity of the inlet channel can be increased. HC and CO can also be reduced.
  • Diesel engines consume less fuel compared to gasoline engines.
  • These engines require low maintenance as compared to petrol engines.
  • A diesel engine generates more torque than a gasoline engine.
  • They generate less CO2 emissions than gasoline engines

Disadvantages of Diesel Engines

  • These engines require a high compression ratio for automatic ignition.
  • A diesel engine has a high chance of crashing as compared to a petrol engine.
  • If this engine will not control properly, it can permanently damage its components under high fire conditions.
  • Diesel fuel may not be as widely available in some areas as gasoline.
  • These engines have a high maintenance cost.
  • Automobiles that have diesel engines are more expensive.
  • Diesel fuel has a high price as compared to petrol fuel.
  • They may be harder to start and operate in cold weather.
  • They are heavier than petrol engines due to their larger size and extra parts.
  • They are louder than gasoline engines.
  • They generate higher nitrogen oxides (NOx) and particulate matter (soot) than gasoline engines.

Applications of Diesel Engines

  1. Marine Vessels: They use to power marine vessels, like cruise ships and cargo ships, because of their high fuel efficiency and torque output and.
  2. Transportation: Diesel engines are most commonly used in cars, tractors, buses, trucks, and other heavy-duty vehicles because of their high fuel efficiency and torque output.
  3. Construction and Industrial Equipment: They use to power different industrial and construction equipment, such as generators, excavators, and bulldozers, because of their capability to ensure high torque and reliable operation in severe situations.
  4. Agriculture: Diesel engines are used to power different agricultural machinery, including harvesters and tractors.
  5. Military: They power different military vehicles and equipment because of their high reliability, durability, and capacity to work in harsh situations.
  6. Locomotives: They are employed in marine vessels and locomotives because of their capability to deliver reliable and efficient power.
  7. Power Generation: The are used in various power generation applications, such as in backup generators for offices, houses, data centers and hospitals.
  8. Mining: Diesel engines power various mining equipment, including excavators and haul trucks.