Reciprocating Engine | How does a Piston Engine Work

The reciprocating engine is one of the most famous types of engine. It is also known as a piston engine. This article explains the reciprocating engine working, types, and applications.

What is a Reciprocating Engine?

A reciprocating engine is a type of engine that uses one or more pistons to transform the thermal energy of the fuel into rotary motion. It is known as a reciprocating engine because of the piston’s reciprocating motion that generates the mechanical power required to complete the task. It is also known as a piston engine. 

These engines have various types, such as an ICE (internal combustion engine), Stirling engine, and ECE (external combustion engine). The Wankel engines can perform the same tasks as the piston engine, but their method of working is very different because of the triangular rotor.

Working of Reciprocating Engine

A reciprocating engine works on the basic principle of converting chemical power (fuel) into mechanical energy (rotary motion). This transformation happens inside the engine cylinder during the combustion process.

A reciprocating engine works in the following way:

1. Suction Stroke
2. Compression Stroke
3. Power Stroke
4. Exhaust Stroke

Reciprocating Engine Working

1) Suction Stroke: –

During the suction stroke, the piston moves downward (From TDC to BDC). As the piston reaches at BDC, a vacuum produces inside the engine cylinder. Due to this vacuum, a pressure difference produces between the cylinder’s internal pressure and atmospheric pressure. This pressure difference causes to suck the fuel into the cylinder through an inlet valve.

During this stroke, the exhaust valve remains closed. 

2) Compression Stroke: –

After the suction process, the piston reciprocates in the cylinder for fuel compression. During the compression stroke, the piston moves upward. As it moves upward, it reduces the volume of the cylinder and compresses the air-fuel mixture.

In this process, the piston transforms the charge (fuel or air-fuel mixture) into high-temperature and high-pressure fuel. At this stage, a spark plug (for gasoline engines) delivers a spark to the air-fuel mixture and ignites the compressed mixture. 

3) Power Stroke: –

As the spark plug ignites the fuel, a high thrust generates, shifting the piston to the BCD (as shown in the above diagram).

As the piston starts rotating, it also rotates the crankshaft through a connecting rod. Therefore, this stroke is known as Power Stroke.

4) Exhaust Stroke: –

After completing the power stroke, the piston again moves from a downward to an upward direction (as shown in the above diagram). It forces the exhaust gases out of the engine cylinder.

Parts of Piston Engine

The reciprocating engine has the following major parts:

• Piston
• Connecting Rod
• Cooling jackets
• Cylinder
• Spark Plug 
• Valves 
• Fuel Injector
• Piston Ring

1) Piston

A piston is the most important component of the piston or reciprocating engine. It has a circular shape. It reciprocates inside the cylinder. The downward and upward movement of the piston helps the engine to suck and compress the fuel.

The piston is directly connected to the crankshaft. It transfers its rotary motion to the crankshaft via a connecting rod.

Read Also: Different types of Engines

2) Cylinder

A cylinder also has a circular design.  It works as a confined space in which the combustion process occurs. The cylinder has a piston that moves up and down for suction and compression.

In different engines, cylinders are settled in different ways, such as a flat arrangement, a W-shape arrangement, a V-shape arrangement, and a horizontal or a single-row arrangement.

3) Connecting Rod

One end of the connecting rod is linked with the crankshaft, while the other end is linked with the piston. The connecting rod uses to deliver the piston’s reciprocating movement to the crankshaft.

Read Also: Working of Connecting rod

4) Crankshaft

A crankshaft is made of hard material. In a reciprocating engine, during the downward movement of the piston, the engine sucks the fuel into the cylinder. During the compression stroke, the crankshaft moves the piston up.

The crankshaft gets the reciprocating motion of the piston via a connecting rod and transforms this motion into rotary motion.

After converting the reciprocating motion into rotary motion, the crankshaft delivers this motion to the vehicle tires and moves the vehicle.

Read More: Working of Crankshaft 

5) Spark Plug

A spark plug is employed in a petrol piston engine. It installs on the cylinder top above the inlet and exhaust valves. This part of the engine uses to burn the compressed air-fuel mixture.

The spark plug ignites the air-fuel mixture as the piston converts it into high-pressure and temperature fuel.

Read More: Bad Spark Plug Symptoms and Causes

6) Fuel Injector

A fuel injector is a part of the piston engine which injects fuel into the cylinder. It also regulates the quality and timing of the injected fuel into the cylinder.

7) Piston Ring

It uses to prevent the cylinder and piston from wear because they are in direct contact. It also removes the additional fuel from the surface of the cylinder into the sump. The piston ring also cleans the piston surface.

This part of the engine delivers a tight sealing so that the air-fuel mixture can’t leak from the cylinder.

8) Valves

A piston engine has two valves that are:

1. Intake valve: When the engine sucks fuel into the cylinder, it enters via an intake valve. An intake valve acts as a non-return valve. It stops the backflow of the fuel.
2. Exhaust Valve: This valve uses to discharge the combustion and exhaust gases from the engine cylinder.

Read Also: Different types of Valves

Types of Reciprocating Engines

The reciprocating engine has two below given major types:

1. ICE (Internal Combustion Engine)
2. ECE (External Combustion Engine

1) Internal Combustion Engine

It is a type of engine in which the fuel combustion process takes place in the combustion chamber. These engines are most commonly used in different vehicles, trains, airplanes, ships, boats, etc.

An IC engine works on the basic principle of the ideal gas law:

                                     PV=nRT

The internal combustion engine further divides into the following types:

i) Spark Ignition (SI) Engine 

A SI engine is a famous type of reciprocating engine in which the ignition process is due to the spark provided by a spark plug.

As the piston compresses the air-fuel mixture inside the compression cylinder and converts it into high pressure and temperature mixture, a spark plug delivers a spark to the compressed mixture and ignites it.

                      SI Engine

In this type of engine, petrol or gasoline uses as a working fluid. 

Read Also: Different types and working of SI Engines

ii) Compression-Ignition (CI) Engine 

In the compression ignition engine, the ignition process occurs due to high compression of the air-fuel mixture.

          source: https://mechanicaljungle.com/

In this engine, as the air-fuel mixture enters the cylinder, the piston compresses it and transforms the mixture into high temperature and pressure air.

The compressed air has such high temperature and pressure when the fuel is injected, the air-fuel mixture ignites itself. In this reciprocating engine, there is no need for a spark plug. Therefore, the CI engine is also known as a self-ignition engine. 

These engines use diesel as a working fluid. Therefore, it is also known as a diesel engine.

Read More: Different types of CI Engines

iii) Two-Stroke Engine

A 2-stroke engine accomplishes a working cycle with one revolution of the crankshaft or two strokes of the piston in the compression chamber. This engine completes a power cycle in two strokes because the intake and exhaust strokes happen at the same time.  

                   Two-stroke Engine

These internal combustion engines produce more pollution. These also have low effectiveness of the fuel. They are utilized to generate electricity for different types of applications such as large boats and powerplant operations.

iv) Four-stroke Reciprocating Engine

A 4-stroke engine accomplishes a working cycle with two revolutions of the crankshaft or four strokes of the piston in the compression chamber. These engines use four strokes of the piston because the intake and exhaust strokes don’t simultaneously.

These engines generate less pollution than two-stroke engines. They also have high fuel effectiveness. But the two-stroke engine has high power than the four-stroke engine.

Read Also: Working of 4-stroke Engine

2) External Combustion Engine

An external combustion engine is an engine where an external source delivers the heat to the working fluid through a heat exchanger. 

These engines have a very low emission rate and are very beneficial for huge power production. But these engines are not best for low-load applications. These also have leakage problems. The Stirling engine is one of the famous types of EC engine.

i) Stirling Engine

A Stirling engine is a single-stage external combustion engine that uses hydrogen, helium, or air as a working fluid. This reciprocating engine has a sealed cylinder with one cold part and the other hot.

                Stirling Engine

In this engine, the working fluid flows from the high-temperature (hot) end to the low-temperature (cold) end through a mechanism. When the fluid is on the hot end, the fluid swells and forces the piston to move upward. The fluid contracts when it returns to the cold end.

A properly designed Stirling engine has two power pulses in one revolution, making it capable of running very smoothly. These engines can become more efficient than typical IC engines.

These engines also have less vibration and noise during the process. But Stirling engines are not very beneficial for applications like airplanes and cars because these can’t start as quickly as an internal combustion engine. Therefore, these engines are mostly utilized in underwater power systems, cooling, and heating applications.

Read More: Stirling Engine Working and Types

Advantages and Disadvantages of Reciprocating Engine

The reciprocating or piston engine has the following major advantages and disadvantages:

Advantages of Piston Engine

• Provide incremental electricity quickly
• Compared to traditional methods, it requires much less water for operation
• These engines have higher electrical efficiencies.
• The heat extraction properties make it best for making hot water.
• These can start and stop quickly.
• Some types of reciprocating engines have self-ignition capabilities, such as diesel engines.
• It can be operated under partial load and has excellent partial load efficiency.
• They require low time for a start-up.
• The piston engine can obtain high thermal efficiency through the normal maximum pressure of the working fluid.
• A piston engine is less expensive than a jet engine.

Disadvantages of Piston Engine

• The reciprocating engine is several times less compact in both volume and weight than a jet engine.
• These engines have high emissions.
• The cooling process of this engine generates lower-grade heat.
• These engines have high relative maintenance costs.
• The reciprocating engine has lower thermal efficiency than the Wankel engine.

Applications of Reciprocating Engines

• Construction: Reciprocating engines are also commonly employed in the construction industries to run heavy machines like cranes, excavators, and bulldozers.
• Marine: They use to power marine vessels, such as submarines, ships, and boats.
• Aircraft: They power aircraft, mainly smaller aircraft such as light helicopters and planes. These engines are usually powered by aviation fuel and are employed to rotate the rotor blades or propeller.
• Power generation: Reciprocating engines are also used in power plants to produce electricity, mainly in remote areas where grid electricity doesn’t exist.
• Automobiles: Reciprocating engines are most commonly used in automobiles, both in commercial vehicles and passenger cars.
• Agriculture: They power various agricultural machinery, including tractors, harvesters, and other farm machinery.
• Industrial: They use to power different industrial applications, such as compressors, pumps, and generators.

Reciprocating Engine VS Wankel Engine

The main difference between the piston engine and the Wankel engine is given below:

Reciprocating Engine	Wankel Engine
These engines have low efficiency.	These engines have more thermal efficiency than piston engines.
The piston engine has a high weight due to many moving parts.	The Wankel engine has low weight than the reciprocating engine.
These engines have a higher number of rotating parts.	These have only a few numbers of rotating parts.
The reciprocating engine has a higher cost than the Wankel engine.	The Wankel engine has a lower cost.
Reciprocating engines generate a characteristic noise.	They usually produce various noises that are usually smoother and quieter.
They have a lower power-to-weight ratio than the Wankel engine.	They have a higher power-to-weight ratio.
They need more maintenance.	They require less maintenance than reciprocating engines.
These engines usually have a cylinder shape.	They usually have a triangular shape.

FAQ Section

what is a non-reciprocating engine

A non-reciprocating is also known as a Wankel engine. It uses a rotary rotor for the compression and combustion cycle instead of a piston.

What are reciprocating engines used for?

The reciprocating engines are used for emergency, standby, backup power, or for larger utility-scale electricity production applications.

What are the Components of the reciprocating engine?

The reciprocating engine has the following major components:

1. Connecting rod
2. Piston
3. Crankshaft
4. Piston cylinder
5. Spark plug
6. Fuel injector
7. EGR valve
8. Fuel tank
9. Fuel pump

Why use reciprocating engines?

• Easy maintenance: They are easy to maintain and replace.
• Flexibility: You can use different fuels such as biofuels, diesel, or gasoline to power these engines. This feature of the reciprocating engine makes it adaptable to various needs and fuel availability.
• Power: They have the ability to produce a lot of power for their size, making them best suitable for applications where a high power-to-weight ratio is needed, like in aircraft, boats, and cars.
• Reliability: Reciprocating engines are famous because of their high durability and reliability, with many engines lasting for thousands of hours with proper maintenance.
• Efficiency: They can be manufactured to be very fuel-efficient, which is vital in applications where fuel consumption is a major cost factor.

Read More

1. Different types of Engines
2. Types of IC Engine
3. Working of Wankel Engine
4. Different Types of EC Engines