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.
Types of engine
In 2022, modern vehicle engines can be more easily understood once divided into the following primary categories, which include:
- Internal combustion engines
- External Combustion Engines
- Hybrid engine (Internal combustion engine + electric engine)
- Electric engine
1. Internal combustion engine.
An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit.
In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some components of the engine. The force is typically applied to pistons (piston engine), turbine blades (gas turbine), a rotor (Wankel engine), or a nozzle (jet engine).
Internal combustion engines (ICE) are the most common form of heat engines, as they are used in vehicles, boats, ships, airplanes, and trains. They are named as such because the fuel is ignited in order to do work inside the engine. The same fuel and air mixture is then emitted as exhaust.
2. External Combustion Engine
An external combustion engine (EC engine) is a reciprocating heat engine where a working fluid, contained internally, is heated by combustion in 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.
They are what fueled the famous steam locomotive with its plume of steam rushing out of its stack. Presently they are used to generate a large of amount of the world’s electricity. Any coal or nuclear-driven power plant is powered by steam engines.
3. Hybrid Engine
Hybrid electric vehicles are powered by an internal combustion engine and one or more electric motors, which uses energy stored in batteries. A hybrid electric vehicle cannot be plugged in to charge the battery.
Instead, the battery is charged through regenerative braking and by the internal combustion engine. The extra power provided by the electric motor can potentially allow for a smaller engine. The battery can also power auxiliary loads and reduce engine idling when stopped. Together, these features result in better fuel economy without sacrificing performance.
4. Electric Engine
An electric engine is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor’s magnetic field and electric current in a wire winding to generate force in the form of torque applied on the motor’s shaft.
All-electric vehicles, also referred to as battery electric vehicles (BEVs), have an electric motor instead of an internal combustion engine. The vehicle uses a large traction battery pack to power the electric motor and must be plugged into a wall outlet or charging equipment, also called electric vehicle supply equipment (EVSE).
Because it runs on electricity, the vehicle emits no exhaust from a tailpipe and does not contain the typical liquid fuel components, such as a fuel pump, fuel line, or fuel tank.
In this article, we’re focusing on the workings of the traditional internal combustion engine and reviewing the most common type of combustion engine used in vehicles today.
Different types of internal combustion (I.C.) engines and their classification depends on different grounds.
Types of Automobile Engine
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
- 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.
- 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.
- 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.
- 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.
- 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:
- Otto cycle engine: These types of engines work on the Otto cycle.
- Diesel cycle engine: The engine working on the diesel cycle is called a diesel cycle engine.
- 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:
- 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.
- 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.
- Hot spot ignition engine: This type of engine is not in practical use.
5. Type of Ignition
On the basis of ignition, the engines are classified as:
- 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.
- 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:
- 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.
- Double cylinder engine: The engine which consists of two cylinders is called a double cylinder engine.
- 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:
- 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.
- Horizontal engine: In horizontal engines, the cylinders are placed horizontal position.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
On the basis of speed, the types of engines are:
- Low-speed engine
- Medium-speed engine
- High-speed engine
2. Method of Fuel Injection
On the basis of the method of fuel injection, the engines are classified as:
- Carburetor engine
- Air injection engine
- Airless or solid injection engine
3. Method of Governing
- 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.
- Qualitatively governed engine
- Quantitatively governed engine
- 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.
- 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.
- Locomotive engine: The engines which are used in trains are called locomotive engines.
- Marine engine: The engines which are used in marines for boat or ship propulsion are called marine engines.
- Aircraft engine: Types of engines that are used in aircraft is called aircraft engine. Radial and gas turbine engines are used in aircraft propulsion.