INTERNAL COMBUSTION ENGINE
Hello guys, in this post we are going to see about the Internal combustion engine with its classifications, parts of internal combustion (ic) engine and working of an Internal combustion engine.
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What is an Internal Combustion (IC) engine?
The type of engine in which the combustion of fuel taking places inside the cylinder of a engine is known as Internal combustion(IC) engine.
Principle of Internal Combustion engine
There are two principles which have been used in reciprocating internal combustion engines are:
The otto cycle was named after The German scientist known as Nikolous Otto for Otto cycle engine
Diesel Cycle:
The Diesel engine was named after the French-born German engineer known as Rudolf Christian Karl Diesel for diesel cycle engine.
Both the otto and Diesel-cycles were used in Two-stroke engine and Four-stroke engine categories.
Classification of Internal Combustion Engines
The IC engines are classified under the basis of following types. They are:
- Gas engine
- Petrol engine
- Light oil engine (kerosene)
- Heavy oil engine (diesel)
- Otto cycle engine
- Diesel cycle engine
- Dual combustion engine
- Low-speed engine
- Medium speed engine
- High-speed engine
- Spark ignition engine
- Compression ignition engine
- Air-cooling engine
- Water-cooling engine
Parts of Internal Combustion(IC) Engines
The cylinders of IC engines are generally made of nickel and cast iron. The body of the cylinder body comprises with the passage of both inlet and outlet of fuel. It is also referred to as the heart of engine. The piston of the engine reciprocates within the cylinder. The cylinder is made up of nickel and cast iron. The cylinder head block contains spark plug and it is fitted along with the atomiser.
It is the small part in a Petrol engine or SI engine which is used to produce spark to burn the fuel.
The part which is only used in a Diesel engine or CI engine for spraying the fuel inside the engine cylinder is called fuel injector.
The Pistons which are generally used in internal combustion(IC) engines moves to the end inside the cylinder. So it is known as trunk pistons.The reciprocating member of the engine which moves with in the cylinder is called Piston. The piston rings are fitted at the top of the piston to prevent the leaking of fuel which passes through the piston. So these rings are known as "compression ring".
The part of the engine which converts the reciprocating motion of piston into rotary motion of crankshaft is called connecting rod.The rod which links between the piston and the crank is called as connecting rod. The end which is connected with piston is called wrist pin or piston pin and the end whichis connected with the crank is called as crank pin. With the help of the connecting rod, the pressure of the working gases is transferred to the Crank.
The rotating member of the engine which makes circular motion inside the crankcase is known as crank. It is made up of steel forging. The body of the crank is rectangular in cross section. The rotating member of the that connects the crank and connecting rod is known as crankshaft. It is placed inside the crank case.
For controlling the fluctuation of speed which is being produced by the fluctuation of energy produced per a cycle of operation, a heavy weight element in the form of a wheel will be mounted on the crankshaft is known as flywheel. It is made of up of cast iron. It is also responsible for storing energy in the form of inertia and also for converting it into mechanical work.
For controlling the speed of the engine due to fluctuation in external load, a controller mechanism is used known as governor. It also connects with the engine crankshaft.
The passage pipe which carries the fresh fuel or air-fuel mixture into the cylinder is known as intake manifold.
It is used because for providing equal amount of fuel to every cylinder in the engine.
The passage pipe which is carries out the exhaust gas from the engine cylinder is known as exhaust manifold.
The piston is accommodated with some ring like structures on it outer surface. It is called Piston rings. The Piston rings fits the fuel tightly between the Piston and the cylinder so that it prevents the leakage of high pressure gas. These rings are made up of special category of cast iron,so it retains elasticity even at very high temperature.
And these rings sealed between the gap cylinder lines and the piston. It is also responsible for carrying the lubricants between those parts, i.e. Piston and Cylinder. The rings which are held nearer to cylinder head are known as “compression rings” and those are held away from the compression rings are known as “oil rings”.
The main part of the valve gear mechanism is called as cam. It is provided for operating the function of opening and closing of both Inlet and Exhaust valves and it also operates the fuel injection pump incase of Diesel engine.The camshaft is driven by the crankshaft at a speed which is the half speed of the crankshaft.
The cam motion is transferred to the valve by means of the pushrod and rocker arm that rotates in a vertical plane about the lever due to rotation produced by the cam.
It is provided for monitoring the motion of the cam.
It is one of the part of the engine which provides shelter for the crank and other engine parts. It also acts as the sump for storing lubricants in it.
The valve which controls the entry of fuel or air-fuel mixture into the cylinder of engine is is called Inlet valve.
The function of this valve is to control the exhaust of the burnt gases from the engine cylinder into the atmosphere.The valve whivh controls the process of removing burnt gas after combustionis known as exhaust valve.
The spring which operates the closing function of valve is known as valve spring.
It is the uppermost end position of the piston at the head of the cylinder.
At TDC the angle of the crank is supposed to be at 0'.
The lower end position of the piston at the end of the crankis called bottom dead center. At BDC, the angle of the crank is supposed to be at 180'.
The distance through which piston moves within the cylinder of the engine during one stroke is known as stroke length. Approximately it is equal to twice the length of the crank. In other words it is said that stroke length is the total distance between the top and bottom dead centers.
The inner diameter of the cylinder of an engine is called cylinder bore.
The volume of the piston at covered in one stoke within the cylinder is known as stroke volume.
The volume which is left between the head of the cylinder and piston at the time when the piston is at either end i.e.,TDC or BDC.
Cycles of IC engines
The internal combustion engine has three basic cycle for operation. They are
1. Otto cycle
2. Diesel cycle
3. Dual combustion cycle
Otto cycle
It consists of two reversible adiabatic, two constant volume process. Heat is supplied during process 2-3 at constant volume and heat is rejected during the process 4-1 at constant volume. During adiabatic process 1- 2 and 3- 4, no heat is supplied rejected.
Diesel cycle
It consists of constant pressure and a constant volume, and two adiabatic processes. Heat is supplied during constant pressure process 2-3 and is rejected during constant volume process 4-1. During adiabatic process 1-2 and 3-4, no heat is supplied or rejected.
Dual combustion cycle
It consists of two constant volume process, two adiabatic processes, and one constant pressure process. Heat is supplied partly at constant volume process 2-3 and partly at constant pressure process 3-4. Heat is rejected at constant volume process 5-1. No heat is added during adiabatic process 1-2 & 4-3.
What is four-Stroke Engine?
If the four events of operation i.e. suction, compression, expansion, and exhaust are completed in 4 strokes of piston i.e. by two revolutions of the crankshaft, the engine is called four stroke engine.
working principle of 4-Stroke Petrol engine
 |
| (Four stroke engine) |
It based on Otto cycle. Inlet valve, exhaust valve, and spark plugs are mounted over the cylinder head. It runs in the following sequence of operation
In this stroke, the Piston moves outward. The pressure within the cylinder falls and the mixture of oil and fuel enters into the cylinder through the inlet valve till the end of the stroke. In this stroke, the exhaust valve will remain closed and no Spark will give by the spark plug.
In the stroke, the Piston moves inward and inlet and exhaust valve are in closed condition. So the charge within the cylinder is compressed adiabatically. At the end of the stroke, the spark plug supplies the spark and burning of charge starts.
As the charge burnt, the high pressure is built up above the piston and for which Piston moves outward and expansion of burnt gas take place adiabatically. So power is produced in this stroke. At the end of the stroke, the exhaust valve open and some of the burnt gases escape into the atmosphere and pressure Falls.
In the stroke, the inlet valve is in the closed condition and the exhaust valve is in open condition and Piston moves inward. So, burn gases are driven out from the cylinder. At the end of the stroke and exhaust valve will close and inlet valve will open to start the next cycle.
Just read our article about Four-Stroke engine with its classifications, to know more.
What is two-Stroke Engine?
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| (Two stroke engine- Yamaha RX100) |
If the basic four events of operation i.e. suction, compression, expansion and exhaust stroke are completed in two-stroke of piston i.e. one revolution of the crankshaft, the engine is called two-stroke engine.
working principle of two-Stroke Petrol engine
The Piston moves upward and first cover the inlet port. So the charge enters into the casing through the inlet port, for the movement of the piston, It covers transfer port and then exhausts port. So the charge above the piston compressed adiabatically. Thus in this stroke suction and compression are completed in single Piston movement. After compression ignition of charge starts by means of the spark plug.
The Piston moves downward due to a force exerted by the burnt gases. So, expansion burnt gases take place. After expansion, it fast uncovers the exhaust port and then transfer port. So, scavenging of burnt gases takes place. For further movement of the piston, it covers the inlet port. Thus, the cycle is repeated.
Just read our article about Two-Stroke engine for more clarifications.
Scavenging and Turbocharging
What is Scavenging in IC Engine?
Scavenging is process in which the removal and cleaning out of burnt gases takes places by the intake of fresh air or fuel mixture in the engine cylinder. This process is known as scavenging.
Supercharging
The process of allowing fresh air or air-fuel mixture in large quantity in the engine cylinder during normal suction is known as supercharging or boosting. The instrument used for the supercharging process is called as supercharger.
The objective of supercharging:
- To increase the output efficiency of the engine.
- To reduce the effect of high altitude.
- To decrease the weight of engine for Per KW power developed.
- Improving the engines to take overloads.
Turbocharger
By using a turbocharger, a large amount of energy within the exhaust gas is used for some other purposes. The released exhaust gas is allowed to expand in a nozzle and a huge quantity of kinetic energy is obtained which is used to drive the exhaust gas turbine.
The exhaust gas turbine is connected to the supercharger. The Combination of a supercharger and exhaust gas turbine is known as turbocharger.
Detonation
Very rapid combustion of the last portion of the Unburnt charge will generate high-pressure waves and unusual sound in the cylinder.
If the ignition temperature is reached and the delay period is shorter then the time is taken by the flame front to reach the last portion of the Unburnt charge, detonation will take place.
Effect of detonation:
- Reverberating shock produced in the combustion chamber.
- Breaking of engine parts due to high-pressure waves.
- Power losses.
- Overheating of spark plug and cause of Pre-ignition.
- Increases heat loss and reduce total thermal efficiency of the engine.
Pre-ignition
The automatic ignition of charge before normal ignition given by spark plug. It occurs in Spark ignition engine.
The overheat carbon deposit on the combustion chamber, exhaust valve, spark plug supply to spark to ignite the fresh charge before the spark plug.
Effects of pre-ignition
- Produces detonation
- Reduce thr output power of the engine.
- Poor engine operation
- Create damages in engine parts due to high temperature.
Firing Order in I.C. Engine
The sequence in which the firing takes place in the different cylinder in a multi-cylinder engine. The Proper firing order can reduce the vibration and ensure the balancing of the engine also provide proper flow of power from different cylinder to the common crankshaft.
Firing order in multi-cylinder engine:
- 3-cylinder engine: 1-3-2
- 4-cylinder engine:1-3-4-2 or 1-2-4-3
- 6-cylinder engine:1-5-3-6-2-4 or 1-2-4-6-5-3
- 8-cylinder engine:1-6-2-5-8-3-7-4 or 1-4-7-3-8-5-2-6
Lubrication of Internal Combustion Engine
- To reduce friction between moving the parts to the minimum extent so that power loss is less.
- To reduce wear and tear of moving parts.
- To cool the system when it is overheated.
- It also provides cleaning processes of removal waste from inside the system.
- To remove excess heat from the engine.
- To improve the efficiency and life span of the engine.
The following parts of I.C. Engine are to be lubricated:
- Main bearing of the crankshaft.
- Big end bearing of the connecting rod,
- Cylinder wall.
- Small end bearing.
- Valves guides.
- Camshaft bearing.
- Camshaft driving gears.
Methods of lubrication system
Splash Method
In this system, a dipper on the lower part of the connecting rod bearing cap enters into the oil through containing lubrication oil with each revolution the crankshaft. The dipper flashes the oil to the upper part of the engine as a fine oil spray which lubricates the cylinder wall, piston ring, big end bearing and small end bearing of the connecting rod.
Forced feed system method
In this system, the oil is pumped to the all lubricating point. The lubricating oil is supplied under pressure by means of a pump operated by the camshaft of the engine.
Cooling system of the Internal Combustion engine
The necessity of cooling:
Cooling of I.C. Engine is necessary because of following ways-
- To prevent damage of engine parts due to high temperature.
- To prevent the breakdown of the lubricating system.
- To prevent overheating valves, its guide/ seats to prevent wear of valves.
- To prevent loss of strength of piston and other parts.
- The purpose of the cooling system is to keep the engine at is efficient temperature (700– 900) at all engine speed and operating condition.
Method of cooling system
It is classified as follows-
1. Air cooled engine
2. Water cooled engine