What is An Engine? – Different Types of Engines

What is An Engine?

An engine is a machine designed to convert one or more forms of energy into mechanical energy. Mechanical heat engines convert heat into work via various thermodynamic processes. Engines – such as the ones used to run vehicles – can run on a variety of different fuels, most notably gasoline and diesel in the case of cars.

The internal combustion engine is perhaps the most common example of a chemical heat engine, in which heat from the combustion of fuel causes rapid pressurization of the gaseous combustion products in the combustion chamber, causing them to expand and drive a piston, which turns a crankshaft.

Unlike internal combustion engines, a reaction engine (such as a jet engine) produces thrust by expelling reaction mass, in accordance with Newton’s third law of motion.

Apart from heat engines, electric motors convert electrical energy into mechanical motion, pneumatic motors use compressed air, and clockwork motors in wind-up toys use elastic energy. In biological systems, molecular motors, like myosins in muscles, use chemical energy to create forces and ultimately motion.

Available energy sources include potential energy, heat energy, chemical energy, electric potential, and nuclear energy. Many of these processes generate heat as an intermediate energy form, so heat engines have special importance.

Some natural processes, such as atmospheric convection cells convert environmental heat into motion. Mechanical energy is of particular importance in transportation but also plays a role in many industrial processes such as cutting, grinding, crushing, and mixing.

Different Types of engines

Probably the most intuitive way to differentiate between them is the type of energy each engine uses for power.


A heat engine is a system that converts heat to mechanical energy, which can then be used to do mechanical work. It does this by bringing a working substance from a higher state temperature to a lower state temperature.

A heat source generates thermal energy that brings the working substance to a high-temperature state. The working substance generates work in the working body of the engine while transferring heat to the colder sink until it reaches a low-temperature state.

During this process, some of the thermal energy is converted into work by exploiting the properties of the working substance. The working substance can be any system with a non-zero heat capacity, but it usually is a gas or liquid. During this process, some heat is normally lost to the surroundings and is not converted to work. Also, some energy is unusable because of friction and drag.

In general, an engine converts energy to mechanical work. Heat engines distinguish themselves from other types of engines by the fact that their efficiency is fundamentally limited by Carnot’s theorem.

There are mainly two types of heat engines – external combustion engines and internal combustion engines.

1.1 Internal combustion engines

The internal combustion engine is an engine in which the burning of fuel occurs in a confined space called a combustion chamber. This exothermic reaction of a fuel with an oxidizer creates gases of high temperature and pressure, which are permitted to expand.

The defining feature of an internal combustion engine is that useful work is performed by the expanding hot gases acting directly to cause movement, for example by acting on pistons, rotors, or even by pressing on and moving the entire engine itself.

This contrasts with external combustion engines, such as steam engines, which use the combustion process to heat a separate working fluid, typically water or steam, which then, in turn, does work, for example by pressing on a steam actuated piston.

The term Internal Combustion Engine (ICE) is almost always used to refer specifically to reciprocating engines, Wankel engines, and similar designs in which combustion is intermittent. However, continuous combustion engines, such as Jet engines, most rockets, and many gas turbines are also internal combustion engines.

Related: What is Internal Combustion Engine?

1.2 External combustion engines

An external combustion engine (EC engine) is a heat engine where an internal working fluid is heated by combustion of an external source, through the engine wall or a heat exchanger. The fluid then, by expanding and acting on the mechanism of the engine produces motion and usable work. The fluid is then cooled, compressed, and reused (closed cycle), or (less commonly) dumped, and cool fluid pulled in (open cycle air engine).

“Combustion” refers to burning fuel with an oxidizer, to supply the heat. Engines of similar (or even identical) configuration and operation may use a supply of heat from other sources such as nuclear, solar, geothermal, or exothermic reactions not involving combustion; but are not then strictly classed as external combustion engines, but as external thermal engines.

The working fluid can be gas as in a Stirling engine or steam as in a steam engine or an organic liquid such as n-pentane in an Organic Rankine cycle. The fluid can be of any composition; gas is by far the most common, although even single-phase liquid is sometimes used. In the case of the steam engine, the fluid changes phases between liquid and gas.

Related: What is External Combustion Engine?

1.3 Air-breathing combustion engines

Air-breathing combustion engines are combustion engines that use the oxygen in atmospheric air to oxidize (‘burn’) the fuel, rather than carrying an oxidizer, as in a rocket. Theoretically, this should result in a better specific impulse than rocket engines.

A continuous stream of air flows through the air-breathing engine. This air is compressed, mixed with fuel, ignited, and expelled as the exhaust gas.


Typical air-breathing engines include:

  • Reciprocating engine
  • Steam engine
  • Gas turbine
  • airbreathing jet engine
  • Turbo-propeller engine
  • Pulse detonation engine
  • Pulse-jet
  • Ramjet
  • Scramjet
  • Liquid air cycle engine/Reaction Engines SABRE.


These types of engines known as jet engines, generate thrust by expelling reactionary mass. The basic principle behind a reactionary engine is Newton’s Third Law basically if you blow something with enough force through the back end of the engine, it will push the front end forward. And jet engines are really good at doing that.

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A reaction engine is an engine or motor that produces thrust by expelling reaction mass, in accordance with Newton’s third law of motion. This law of motion is commonly paraphrased as: “For every action force there is an equal, but opposite, reaction force.”

Examples include jet engines, rocket engines, pump jets, and more uncommon variations such as Hall effect thrusters, ion drives, mass drivers, and nuclear pulse propulsion.

The discovery of the reaction engine has been attributed to the Romanian inventor Alexandru Ciurcu and to the French journalist Just Buisson.


There are three types of classical electrical engines: magnetic, piezoelectric, and electrostatic.

The magnetic one, like the battery there, is the most commonly used of the three. It relies on the interaction between a magnetic field and electrical flow to generate work. It functions on the same principle a dynamo uses to generate electricity, but in reverse. In fact, you can generate a bit of electrical power if you hand crank an electrical-magnetic motor.

To create a magnetic motor, you need some magnets and a wound conductor. When an electrical current is applied to the winding, it induces a magnetic field that interacts with the magnet to create rotation.

It’s important to keep these two elements separated, so electrical motors have two major components: the stator, which is the engine’s outer part and remains immobile, a rotor that spins inside it.

The two are separated by an air gap. Usually, magnets are embedded into the stator and the conductor is wound around the rotor, but the two are interchangeable. Magnetic motors are also equipped with a commutator to shift electrical flow and modulate the induced magnetic field as the rotor is spinning to maintain rotation.

Piezoelectric drives are types of engines that harness some materials’ property of generating ultrasonic vibrations when subjected to a flow of electricity in order to create work.

Electrostatic engines use like-charges to repulse each other and generate rotation in the rotor. Since the first use expensive materials and the second requires comparatively high voltages to run, they’re not as common as magnetic drives.

Classical electrical engines have some of the highest energy efficiency of all the engines out there, converting up to 90% of energy into work.


Some motors are powered by potential or kinetic energy, for example, some funiculars, gravity planes, and ropeway conveyors have used the energy from moving water or rocks, and some clocks have a weight that falls under gravity. Other forms of potential energy include compressed gases (such as pneumatic motors), springs (clockwork motors), and elastic bands.

Historic military siege engines included large catapults, trebuchets, and (to some extent) battering rams that were powered by potential energy.

Pneumatic motor

A pneumatic motor is a machine that converts potential energy in the form of compressed air into mechanical work. Pneumatic motors generally convert compressed air to mechanical work through either linear or rotary motion.

Linear motion can come from either a diaphragm or piston actuator, while rotary motion is supplied by either a vane-type air motor or piston air motor. Pneumatic motors have found widespread success in the hand-held tool industry and continual attempts are being made to expand their use to the transportation industry. However, pneumatic motors must overcome efficiency deficiencies before being seen as a viable option in the transportation industry.

Hydraulic motor

A hydraulic motor derives its power from a pressurized liquid. This type of engine is used to move heavy loads and drive machinery.


Some motor units can have multiple sources of energy. For example, a plug-in hybrid electric vehicle’s electric motor could source electricity from either a battery or from fossil fuels inputs via an internal combustion engine and a generator.

different types of Engines

Basically, Thermal engines are of two types, and these are external combustion engines and internal combustion engines.

There are different types of internal combustion (I.C.) engines and their classification depends upon various bases.

The I.C. engines are classified on the following basis:

1. Types of Design

  1. Reciprocating engine: In a reciprocating engine, there is a piston and cylinder, the piston does reciprocate (to and Fro) motion within the cylinder. Due to the reciprocating motion of the piston, it is called a reciprocating engine. 2 stroke and four-stroke engines are common examples of reciprocating engines.
  2. Rotary engine: In the rotary engine, the rotor does a rotary motion to produce power. There is no reciprocating motion. A rotor is present in the chamber which does rotary motion inside a chamber. Wankel rotary engines and turbine engines are the rotary types of engines.

2. Types of Fuel Used

On the basis of the types of fuel used, the engine is classified as a petrol engine, diesel engine, and gas engine.

  1. Gasoline engine: In the gasoline engine, gasoline (petrol) is used as fuel. A mixture of gasoline and air is prepared outside the cylinder and an electric spark plug is used to initiate combustion of the compressed charge.
  2. Diesel engine: The diesel engine utilizes a compressed mixture of air and diesel prepared inside the cylinder as fuel. The heat of compression is utilized to initiate the combustion of the mixture.
  3. Gas engine: In the gas engine combustible gases are used as fuel. These engines are not commonly used in automobiles.

3. Cycle of Operation

On the basis of a cycle of operation, the engine types are:

  1. Otto cycle engine: These types of engines work on the Otto cycle.
  2. Diesel cycle engine: The engine working on the diesel cycle is called a diesel cycle engine.
  3. Dual cycle engine or semi-diesel cycle engine: The engine that works on both diesel, as well as Otto cycle, is called a dual cycle engine or semi-diesel cycle engine.

4. Number of Strokes

On the basis of a number of strokes, the types of engines are:

  1. Four Stroke Engine: It is an engine in which the piston moves four times i.e.,2 upward (form BDC to TDC) and 2 downward (from TDC to BDC) movement in one cycle of the power stroke is called a four-stroke engine.
  2. Two Stroke Engine: The two-stroke engine completes the thermodynamic cycle in two strokes of the piston (one revolution of the crank). The engine in which the piston does two times motion i.e., one from TDC to BDC and the other from BDC to TDC to produce a power stroke is called a two-stroke engine.
  3. Hot spot ignition engine: This type of engine is not in practical use.
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5. Type of Ignition

On the basis of ignition, the engines are classified as:

  1. Spark ignition engine (S.I. engine): A spark ignition engine is either a gasoline engine or a gas engine. The electrical energy required to produce a spark in the spark plug is obtained either from a battery or a magneto.
  2. Compression ignition engine (C.I. engine): Compression ignition engines are diesel engines in which air is highly compressed to raise its temperature and initiate combustion when diesel fuel is injected.

6. Number of Cylinders

An engine may be a single-cylinder engine or a multi-cylinder engine. In a single-cylinder engine, there is only one cylinder, whereas in a multi-cylinder engine there is more than one cylinder. The pistons of all the cylinders are connected to the common crankshaft. Therefore, types of engines may be:

  1. Single-cylinder engine: An engine that consists of a single-cylinder is called a single-cylinder engine. Generally, single-cylinder engines are used in motorcycles, scooters, etc.
  2. Double cylinder engine: The engine which consists of two cylinders is called a double cylinder engine.
  3. Multi-cylinder engine: An engine that consists of more than two cylinders is called a multi-cylinder engine. The multi-cylinder engine may have three, four, six, eight, twelve, and sixteen cylinders.

7. Arrangement of Cylinders

On the basis of the arrangement of cylinders, the engines classification is:

  1. In-line Cylinder Engine: The in-Line cylinder engine is a multi-cylinder engine, with all the cylinders arranged in one straight line. Each cylinder has an independent crank.
  2. Horizontal engine: In horizontal engines, the cylinders are placed horizontal position.
  3. Radial engine:  The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders radiate outward from a central crankcase like the spokes of a wheel. When it is viewed from the front, it resembles a stylized star and is called a ‘star’ engine. Before the gas turbine engine does not become predominant, it is commonly used for aircraft engines.
  4. V-engine: The V cylinders engine has two cylinders inclined at 90° to each other. The connecting rods are connected to a common crank pin. There is a common crank for both cylinders. The angle between the two banks is kept as small as possible to prevent vibration and balancing problems.
  5. V-8 Engine: In the V-8 engine design there are two blocks inclined at 90° to each other and each block has four cylinders.
  6. W type engine: In w-type engines, the cylinders are arranged in three rows such that it forms W w-type arrangement. W type engine is made when 12 cylinder and 16-cylinder engines are produced.
  7. Opposed cylinder engine: In an opposed cylinder engine, the cylinders are placed opposite each other. The piston and the connecting rod show identical movement. It runs smoothly and has more balance. The size of the opposed cylinder engine increase because of its arrangement.

8. Valve Arrangement

According to the valve arrangement of the inlet and exhaust valve in various positions in the cylinder head or block, the automobile engines are classified into four categories. These arrangements are named ‘L’, ‘I’, ‘F’, and ‘T’.  It is easy to remember the word ‘LIFT’ to recall the four-valve arrangement.

  1. L-head engine: In these types of L-head engines, the suction and exhaust valves are arranged side by side in the cylinder block. The cylinder and combustion chamber forms an inverted L.
  2. I-head engine: In the I-head engine the suction and exhaust valves are arranged in the cylinder head. A single valve actuates all the valves. These types of engines are mostly used in automobiles.
  3. F-head engine: It is a combination of I-head and F-head engines. In the F-head engine, one valve is in the cylinder block and the other valve is in the cylinder head. Both the sets of valves are operated by a single camshaft.
  4. T-head engine: In T-head engines, the suction valve (SV) and the exhaust valve (EV) are on the cylinder block in opposite directions. Here two camshafts are required to operate, one for the inlet valve and the other one for the exhaust valve.

9. Types of cooling

On the basis of types of cooling, the engines are classified as:

9.1 Air-cooled engines

Air-cooled engines have fins to radiate heat into the surrounding air. The fins are made triangular in shape as they increase the cooling surface area. These fins are made of aluminum, which is a good conductor of heat.

Air-cooled engines run at higher temperatures because air is not a good conductor of heat. The air-cooled engines are generally used in motorcycles and scooters.

9.2 Water-cooled engines

Water-cooled engines require the circulation of water. All automobile engines, which are water-cooled, are fitted with radiators. The radiator offers resistance to the flow of air through the passages in between the small diameter tubes carrying hot water. Therefore, an induced draught fan is provided at the back of the radiator. This fan creates the pressure difference required to get an increased flow of air.

Similarly, to get pressure difference and to overcome the resistance in the water flow at the jackets of the engine, a water pump is provided which draws water from the radiator and forces it into the water jacket of the engine.

Water is not allowed to rise to a higher temperature, as at higher temperatures scale formation takes place. Scale formation causes local heating due to poor cooling as scales are bad conductors of heat. Such local heating may lead to detonation, which may damage engine parts.

Water-cooled engines are used in cars, buses, trucks, and other four-wheeled vehicles, heavy-duty motor vehicles.

Besides the above types of engines, the internal combustion engine is also classified on the basis of the following.

1. Speed:

On the basis of speed, the types of engines are:

  1. Low-speed engine
  2. Medium-speed engine
  3. High-speed engine

2. Method of Fuel Injection

On the basis of the method of fuel injection, the engines are classified as:

  1. Carburetor engine
  2. Air injection engine
  3. Airless or solid injection engine
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3. Method of Governing

  1. Hit and miss governed engine: It is an engine type in which the entry of the fuel is controlled by the governor. It controls the speed of the engine by cutting off the ignition and fuel supply of the engine at a very high speed.
  2. Qualitatively governed engine
  3. Quantitatively governed engine

4. Application

  1. Stationary engine: Stationary engine is an engine in which its framework does not move. It is used to drive immobile equipment like pumps, generators, mills or factory machinery, etc.
  2. Automotive engine: These are the types of engines that are used in the automobile industry. For example, petrol engine, diesel engine, and gas engine are internal combustion engines that falls in the category of an automotive engine.
  3. Locomotive engine: The engines which are used in trains are called locomotive engines.
  4. Marine engine: The engines which are used in marines for boat or ship propulsion are called marine engines.
  5. Aircraft engine: Types of engines that are used in aircraft is called aircraft engine. Radial and gas turbine engines are used in aircraft propulsion.


What is called an engine?

An engine, or motor, is a machine used to change energy into a movement that can be used. The energy can be in any form. Common forms of energy used in engines are electricity, chemical (such as petrol or diesel), or heat. When a chemical is used to produce the energy it is known as fuel.

What do you mean by engine?

An engine is a machine for converting any of various forms of energy into mechanical force and motion also: a mechanism or object that serves as an energy source of black holes may be the engine for quasars.

Is it a motor or an engine?

“People use both interchangeably, but the difference is that motors run on electricity and engines run on combustion. The engine converts various forms of fuels into mechanical force, while the motor transforms electrical energy into mechanical energy.”

What is engine in a car?

The engine is the part of a vehicle that burns fuel and converts it into mechanical power. In most vehicles, this is done using an internal combustion engine, which ignites the fuel and uses it to move mechanical parts.

What is a nickname for an engine?

A machine with moving parts that converts power into motion. motor. machine. dynamo.

What is the function of the engine?

The engine is the vehicle’s main source of power. The engine uses fuel and burns it to produce mechanical power.

What is engine and its types?

Basically, the engines are of two types, and these are external combustion engines and internal combustion engines. External combustion engine: In an external combustion engine, the combustion of fuel takes place outside the engine. Example: the steam engine.

How are engines named?

The letters and numbers that make up an engine’s model number are a series of codes to tell you the engine family, the number of cylinders, the emissions standard, the type of ignition, the capacity, the type of aspiration, and the generator set rating.

Who had the first V8 engine?

Frenchman Leon Levavasseur was a 39-year-old inventor in 1902 when he took out a patent for the first V-8 engine he called the Antoinette. The V8 since then has become the most reliable and efficient internal combustion engine to power automobiles and to see extensive use in powerboats and early aircraft.

Do Car Engines have names?

Browsing through new car information often seems a needlessly complicated task. It should be noted that some manufacturers do not always give a specific name for their petrol engines. Any manufacturers who do so are noted with No Designation (N/D).

What is the part of engine?

The different parts that make up your car’s engine consist of the engine block (cylinder block), the combustion chamber, the cylinder head, pistons, the crankshaft, the camshaft, the timing chain, the valve train, valves, rocker arms, pushrods/lifters, fuel injectors, and spark plugs.

Can engines be electric?

The traditional gasoline engine is replaced by an electric motor that gets its power from the electricity in rechargeable batteries. A gasoline engine tends to look like a plumbing process with its fuel, while an electric vehicle is a wiring process with an electric motor.

What is engine speed?

Engine “Revs” are a measure of the engines speed. Engines are rotating machines and the speed is measured in revolutions per minute – that is how many full turns the engine does every minute. The faster the engine runs, the more complete rotations it does per minute and the more power it produces.

Who invented engine?

1876: Nikolaus August Otto patented the first four-stroke engine in Germany. 1885: Gottlieb Daimler of Germany invented the prototype of the modern gasoline engine.

What is the most common engine?

Inline or Straight: This is the most common engine found in cars, SUVs, and trucks. The cylinders are upright, side by side which makes the engine compact and effective

What are the 5 engine systems?

The Five Types Of Engine Systems:

  • Piston- Otto or Diesel.
  • Turbine- Jet or Turbo Prop.
  • Electrical- Battery or Fuel Cell.
  • Hybrid- Electric, Air, Hydraulic.
  • New Engine Type- A combination of all types in one.

What are the Different Types of Engines?

Types of engines and how they work:

  1. Heat engines– Internal combustion engines (IC engines), External combustion engines (EC engines), Reaction engines.
  2. Electrical engines.
  3. Physical engines.

What was the first engine?

In 1872, American George Brayton invented the first commercial liquid-fueled internal combustion engine. In 1876, Nicolaus Otto, working with Gottlieb Daimler and Wilhelm Maybach, patented the compressed charge, four-stroke cycle engine. In 1879, Karl Benz patented a reliable two-stroke gas engine.

What is the difference between an engine and a motor?

“People use both interchangeably, but the difference is that motors run on electricity and engines run on combustion. The engine converts various forms of fuels into mechanical force, while the motor transforms electrical energy into mechanical energy.”

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