Internal combustion engines
As the name implies or suggests, the internal combustion engines (briefly written as I.C. Engine) are those engines in which the combustion of fuel takes place inside the engine cylinder.
In other words, the internal combustion engines are those engines in which the combustion of fuel takes place inside the engine cylinder by a spark. These are petrol, diesel and gas engines.
An engine is a device, which by using chemical energy of the fuel, transforms it into thermal energy by combustion, to produce mechanical work. We have seen in steam engines that the fuel, fed into the cylinder, is in the form of steam which is already heated and is ready for work in the combustion cycle of the engine.
But in the case of internal combustion engines, the combustion of fuel takes place inside the engine cylinder by a spark and produces very high temperature as compared to the steam engine.
1. Difference between the Steam engines and Internal Combustion Engines.
2. Types of Engines
There are two types of engines
- External combustion engines
- Internal combustion engines
External combustion engines – If the combustion of fuel place outside the engine cylinder, it is an external combustion engine. Ex: Steam turbine, Gas Turbine, Steam Turbine etc.
Internal combustion engines – If the combustion fuel takes place inside the engine cylinder, it is an internal combustion engine. Ex: Petrol engine, Diesel Engine.
3. Classification of Internal Combustion Engines
Internal Combustion Engines may be classified according to the different parts of the Internal Combustion Engines are as follows,
- Working Cycle Employed
- Two-stroke Engine
- Four-stroke Engine
- Fuel Used
- Gas Engine
- Nature Of Thermodynamics Cycle Used
- Otto Cycle
- Diesel Cycle
- Dual Cycle
- Methods Of Cooling
- Air Cooling
- Water Cooling
- Speed Of The Engine
- High-speed Engine
- Medium-speed Engine
- Low-speed Engine
- Field Of Application
- Stationary Engine
- Automobile Engine
- Portable Engine
- Aero Engine
- Method Of Ignition
- Spark-ignition Engine
- Compression Ignition Engine
- Arrangement Of The Engine Cylinder
- Horizontal Engine
- Verticle Engine
- Radial Engine
- V-type Engine
4. Parts of Internal Combustion Engines
- The cylinder is made up of steel or aluminium alloys.
- In this Piston makes to and for a motion to develop power.
- It will withstand high pressure and temperature.
4.2 Cylinder Head
- Cylinder Head is fitted at the top of the cylinder.
- It is made up of steel or aluminium alloys.
- It is made by casting.
- A copper or asbestos gasket is provided in between the cylinder and the cylinder head to make it airtight.
- It is made of aluminium alloys.
- The main function is to transmit force exerted by burning of charge to connecting rod.
4.4 Piston Rings
- These are circular rings made up of special steel alloys.
- these are housed in circumferential grooves of the piston.
- Two sets of rings are provided, with an upper ring to prevent leakage of burnt gases into the lower portion, while lower ring to prevent leakage of oil into the Engine Cylinder.
- They retain elastic properties even at a higher temperature.
- The rings are provided with an airtight seal.
- These are provided on the cylinder head,
- Inlet valve is used to take fresh mixture into the cylinder.
- The exhaust valve is used to expel burnt gases from the cylinder.
4.6 Connecting Rod
- It is a link between the piston and the crankshaft.
- The function of Connecting Rod is to transmit the force from piston to crankshaft.
- It is made of special steel alloys.
- The function of the crankshaft is to convert the reciprocating motion of a piston into rotary motion with the help of connecting rod.
- The crankcase is made of cast iron.
- It holds the cylinder and crankshaft of an engine.
- It also serves as a sump (storing place) for lubricating oil.
- It is big solid wheel mounted on a crankshaft of an IC Engine.
- The main function of the flywheel is to maintain speed constant.
- It stores excess energy during power and gives out during the compression stroke.
5. Working Principle Of Internal Combustion Engines
In IC engines (internal combustion engines) the combustion of takes place inside the cylinder, therefore the thermal energy of the fuel is directly converted into mechanical work.
the IC engine has a higher thermal efficiency than the thermal efficiency of EC engines. In internal combustion engines, when
We know that when the engine returns back to the stroke where it starts we say that one cycle has been completed.The IC engine has four steps to complete one cycle as follows:
Suction Stroke In this stroke the fuel vapour, in the correct proportion, is supplied to the engine cylinder.
Compression Stroke In this stroke, the fuel vapour is compressed in the engine cylinder.
Expansion Stroke In this stroke, the fuel vapour burn by the spark plug is provided on the top of the engine cylinder. when the fuel is burned suddenly raise the pressure, due to the expansion of the combustion products in the engine cylinder. The rise of the pressure pushes the piston with a high force and rotates the crankshaft. The crankshaft, in turn, drives the machine connected to it.
Exhaust Stroke In this stroke, the burnt gases are exhausted from the engine cylinder, so as to make space available for the fresh fuel vapour.
5.1 Working principle of the Four Stroke Petrol Engine
The four-stroke engine consists of spark plug fitted at the top of the cover to indicate the ignition of the air and fuel mixture.
The mixture supplied to the cylinder from the carburettor. This engine works on the principle of the auto cycle known as constant volume cycle. The piston performs four strokes to complete one working cycle.
5.1.1 Suction Stroke
- In this stroke, The inlet valve of the engine cylinder is open and the air-fuel mixture enters into the cylinder. the piston moves from top dead centre to bottom dead centre.
5.1.2 Compression stroke
- In this stroke, Both the inlet and exhaust valves are closed and the piston moves from Bottom dead centre to top dead centre.
- When the piston moves up it compresses the air petrol mixture as the result of compression the temperature and pressure of the mixture will increases.
- The mixture is ignited by the spark plug. The combustion of petrol releases the hot gas which increases the pressure.
5.1.3 Expansion Stroke
- In this stroke, both the inlet and exhaust valve are closed. the piston moves from top dead centre to bottom dead centre.
- The burnt gas produces the high pressure of force to piston perform this stroke and the expansion of hot gases takes place during the process.
- The piston produces the mechanical work which is transmitted to the crankshaft.
- At the end of this stroke, the exhaust valve is open to release the gas into the atmosphere.
5.1.4 Exhaust Stroke
- In this stroke, the exhaust valve is open and the piston moves from bottom dead centre to top dead centre.
- The piston pushes out the product of combustion from the engine cylinder to the atmosphere to do mechanical work.
- At the end of this stroke, the exhaust valve is closed and the same cycles are happening repeatedly.
5.2 Working principle of Four Stroke Diesel Engine
The four-stroke diesel engine is the same as that of petrol engine accept fuel injector instead of a spark plug and the fuel is supplied to the injector by means of a fuel pump.
The diesel engine work on the principle of the theoretic diesel cycle known as constant pressure cycle. It is also known as CI engine because the ignition takes place due to heat produced in the cylinder at the end of the compression stroke.
The piston perform following strokes,
5.2.1 Suction Stroke
- In this stroke, the inlet valve is open and pure air enters into the cylinder.
- The piston moves from the top dead centre to bottom dead centre into the cylinder. At the end of this stroke, the inlet valve closed.
5.2.2 Compression Stroke
- In this stroke, both the valve are closed and the piston moves from BDC (bottom dead centre) to TDC (Top dead centre).
- As the piston is compressing the air and increase temperature and pressure of the air considerably as shown in fig.
- It is represented by 2-3 the ratio of compression 1:20 to 1:22 at the end of this stroke the oil spreads into the cylinder through the injector the high temperature of air ignite the diesel and combustion takes place.
5.2.3 Expansion Stroke
- In this stroke, both the valves are closed and the piston moves from TDC to BDC.
- The burnt gases released by combustion of diesel forces. The piston to moves from TDC to BDC and expansion of the burnt gases takes place at constant pressure.
- It is represented by line 4-5 in fig. During the expansion, piston produces mechanical work which is transmitted to the crankshaft as shown in fig.
5.2.4 Exhaust Stroke
- In this stroke, The exhaust valve is open and the piston moves from BDC to TDC.
- The movement of the piston pushes out the products of combustion from the engine cylinder through the exhaust valve into the atmosphere.
- This completes the cycle and the engine cylinder is ready to suck the fresh air once again.
5.3 Two-Stroke Cycle Petrol Engine
A two-stroke cycle petrol engine was devised by Duglad Clerk in 1880. In this cycle, the suction, compression, expansion, and exhaust takes place during two strokes of the piston. It means that there is one working stroke after every revolution of the crank-shaft.
In other words, it takes only one revolution or only two-strokes to complete the working cycle. A two-stroke engine has ports instead of valves. All four stages of a two-stroke petrol engine are described below.
- In this stage, the piston, Initially the piston is at TDC, while going down, uncovers the inlet port and fresh fuel-air mixture flows into the engine cylinder from the crankcase.
- In this stage, the piston, while moving up, first covers the inlet port and then exhaust port. After that, the fuel is compressed as the piston moves upwards.
- In this stage, the valve opens and fresh fuel-air mixture enters with the crankcase.
- Shortly the piston reaches the TDC (During compression stroke), the charge is ignited with the help of a spark plug.
- It suddenly increases the pressure and temperature of the products of combustion. But the volume remains constant.
- Due to a rise in the pressure, the piston is pushed downward with a great force.
- The hot burnt gases expand due to a high speed of the piston. During this expansion, some of the heat energy produced is transformed into mechanical work.
- In this stage, the exhaust valve is opened as the piston moves downwards. The products of combustion, from the engine cylinder, are exhausted through the exhaust valve into the atmosphere.
- This completes the cycle and the engine cylinder is ready to suck the charge once again.
5.4 The-Stroke Cycle Diesel Engine
A two-stroke cycle diesel engine also has one working stroke after a revolution of the crankshaft. All the four stages of a two-stroke cycle diesel engine are described here:
- In this stage the piston, while going down uncovers the inlet port and fresh air flows into the engine cylinder from the crankcase
- In this stage the piston, while moving up, first covers the inlet port and then exhaust port.
- After that, the fuel is compressed as the piston moves upwards. In this stage, the valve opens and the fresh air enters into the crankshaft.
- Before the piston reaches the TDC the fuel oil is injected into the engine cylinder through the nozzle know as fuel injection valve.
- At this moment, the temperature of the compressed air is sufficiently high to ignite the fuel.
- It suddenly increases the pressure and temperature of the product of combustion.
- Due to increased pressure, the piston is pushed with a great force. The hoe burnt gases expand due to a high speed of the piston.
- During the expansion, some of the heat energy produced is transformed into mechanical work.
- In this stage, the exhaust valve is opened and the piston moves downwards, the products of combustion from the engine cylinder are exhausted through the exhaust valve into the atmosphere.
- This completes the cycle and the engine cylinder is ready to suck the air once again.
6. Difference Between Petrol Engine and Diesel Engine
The main difference between a petrol engine and a diesel engine is a petrol engine draws a mixture of petrol and air during the suction stroke. And a diesel engine draws only air during the suction stroke.
The petrol engine works on Otto cycle. It is easy to start, lighter and cheaper, It has high running cost and low maintenance cost.
The diesel engine works on the diesel cycle. It difficult to start, heavier and costlier, It has low running cost and high maintenance cost.
The petrol engines thermal efficiency is about 26%. These are high-speed engines and used in light-duty vehicles. Where diesel engines thermal efficiency is about 40%. These are low-speed engines and used in heavy-duty vehicles.
That’s it, thank you for reading. If you have any questions leave a comment, Share wit h your friends if you find this article helpful.
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