Internal Combustion (IC) Engine and its Components

In previous blog, we have discussed about IC engine and before jumping to this blog, readers are requested to visit the link given below:
IC Engine

Engine or motor is a device designed to convert one form of energy into mechanical energy. The arrangement of different parts of four stroke spark ignition engine (Petrol engine) and four stroke compression ignition engine (Diesel engine) is shown in the figure below:

                                          Figure: Four Stroke Petrol Engine

                                        Figure: Outline of Diesel Petrol Engine

The purpose of each part is described in short:

1.      Cylinder

The cylinder of IC engine is considered as main body of engine in which piston reciprocates to develop power. It has to withstand very high pressure of about 70 bar and temperature of about 2200^o C because there is direct continuous combustion inside the cylinder. So its material should retain strength at high temperatures without any deformation, should be good conductor of heat and should be able to resist to wear and tear due to reciprocating parts. Generally, ordinary cast iron is used but incase of heavy duty engines, alloy steels are used.

2.      Cylinder head

The cylinder seals one end of the cylinder. It houses the inlet, spark plug and exhaust valve through which the mixture of air and fuel is taken and burnt with the help of spark produced by spark plug and burnt gases are exhausted to the atmosphere from exhaust. A copper and asbestos gaskets are provided between the cylinder and cylinder heat to obtain a gas tight joint.

3.      Piston and piston rings

The primary function of piston is to compress the air fuel mixture during compression stroke and to transmit the gas force to the connecting rod and then to the crank during power stroke. Generally, the piston of IC engine are made up of cast iron, cast steel and aluminium alloy. Often piston is considered as heart of the engine.

The piston rings are placed in the circumferential grooves provided on the outer surface of the piston. It gives gastight fitting between piston and cylinder and prevents from the leakage of high pressurized gases. It is made from special grade cast iron which can retains its elastic property at very high temperatures. The upper piston rings are called compression rings and lower piston rings are called the oiling or oil control rings.

4.      Connecting rod

Connecting rod joins piston with crank. It is usually a steel forging of circular, rectangular, I, T, or H section and is highly polished for increased endurance strength. Its small ends forms a hinge and pin joint with piston and its big end is connected to the crank by crank pin. It has a passage for the transfer of lubricants from the big end bearing to small end bearing also known as gudgeon pin.

5.      Crank and crankshaft

The crankshaft is the backbone of the engine. The main function of crankshaft is to take power produced by engine and transmit it to the output shaft. Both crank and crankshafts are steel forged and machined to a smooth finish. Both are held together with the help of key. Crankshaft is supported in the main bearings held by engine block and has a heavy wheel, known as flywheel, to even out the fluctuations of torque. The power required for any useful purpose is taken out from crankshafts only.

6.      Piston pin or Wrist pin

The piston pin provides the bearing for the oscillating small end of the connecting rod.

7.      Inlet valve

This valve is responsible for the injection of air fuel mixture into the cylinder during suction stroke of the engine. It is controlled by cam shaft mounted on top of it.

8.      Exhaust valve

This valve is responsible for the removable of burnt gases from the cylinder after the power stroke. It is also controlled by cam shaft mounted on top of it.

9.      Valve spring

It is used to keep valves closer to each other.

10.  Inlet manifold

It is the path from where air fuel mixture is carried from carburetor to the petrol engine.

11.  Exhaust manifold

It is the passage from which carries the exhaust gases from exhaust valve to the atmosphere.

12.  Cam shaft

The function of cam shaft is to control the motion of intake and exhaust valves through the cams, cams follower, push rods and rocker arm. The cam shaft is driven positively from the crankshaft and is connected with timing chain.

13.  Cam and cam follower

It is made of a required profile to give desired motion to the valves through the followers.

14.  Push rod and rocker arm

Push rod and rocker arm transmits the motion of cam to the valves. These links together are also called valve gear.

15.  Crank case

It is the base which holds the cylinder and the crankshaft. It also serves as the sump for lubricating oil.

16.  Water jacket

It serves as cooling device for the engine operating at high temperatures.

17.  Bed plate

The lower portion of the crank case is also known as the bed plate. For concrete foundations, bed plates are hold the bed bolts.

18.  Flywheel

It is the wheel mounted on the crankshaft which stores the excess energy during the power stroke and returns the energy into the other strokes and maintains a fairly consant output torque on the crankshafts.

19.  Governor

The function of the governor is to regulate the air fuel mixture in case of petrol engine and amount of fuel in case of diesel engine to maintain a constant speed of the engine. It is run by a drive from the crankshaft.

20.  Carburetor

The function of carburetor is to supply the uniform mixture is air and fuel to the cylinder of petrol engine through the intake manifold. The mass of mixture entering the cylinder is controlled by the throttle valve.

21.  Spark plug

The function of spark plug is to ignite the air fuel mixture after completing the compression in the petrol engine. It is generally mounted on the cylinder head. This is not used in diesel engine.

22.  Fuel pump

It forces the fuel at high pressure through the fuel nozzle into the cylinder at the end of compression stroke in diesel engine.

23.  Fuel nozzle

The function of fuel nozzle is to break up the liquid fuel into a fine spray as it enters the cylinder for proper combustion. It is used in diesel engine.

YV Nitesh

13^th Jan 2019

Internal Combustion Engine

Heat Engine

An Engine is defined as a mechanical device which converts one form of energy into mechanical energy. The transformation of one form of energy into another required form is always associated with losses, therefore, the efficiency conversion plays an important role. Heat is considered as poor form of energy where mechanical work is considered rich form of energy as its back conversion with very high efficiency (90-95%) is possible. In every heat engine, some form of fuel (solid, liquid, gas or nuclear) is used. The chemical or nuclear energy of fuel is converted into thermal energy and that is further converted into mechanical energy to perform some useful work.

The heat engines are classified as;     

a.       External Combustion Engines,

b.      Internal Combustion Engines (IC Engine)

An External Combustion Engine is a thermal power plant as shown in the figure where fuel is burned and its heat is given to the water to generate steam which further used for power generation. The working fluid is not mixed with fuel, therefore, the same working fluid (water) is used again and again in the system. Trains in development phase used external combustion engine and they were also called as Steam Engine.

The Internal Combustion Engine is a gas turbine plant as shown in figure below where fuel is mixed with air and burned. The hot gasses are passed through the turbines to generate power and then the gases are exhausted through exhaust valve. In this case same working fluid cannot be used over again and again in the repeated cycle. During next cycle, again, the fresh air is taken and mixed with fuel for next power stroke.

In above described internal combustion system, compression, combustion and expansion are carried out in different components. But in conventional IC engines, all the above mentioned processes (suction, compression, ignition and exhaust) are carried out inside cylinder and piston only. The simple arrangement is shown below:

Development of IC Engine:

1.      Hugens’ Gunpowder Engine:

The first IC engine was developed in the year 1680 by Dutch physicist Hugens using gunpowder as fuel. It consists of cylinder and piston and has arrangement as shown in the figure below:

The upward stroke of the piston was caused by the explosion of gun powder and the return stroke was caused by the atmospheric pressure acting on the other side of the piston and arising from the pressure drop in the cylinder as the gasses starts to cool. The engine worked with a single explosion charge and he was unable to produce sequential explosion necessary for continuous operation.

2.      The Lenoir Engine:

In 1860, Lenoir developed non-compression type gas engine using coal gas as fuel. This engine was similar to double acting steam engine except a mixture of gas and air was used as working fluid instead of steam. The efficiency of this engine was considerably low because of low expansion ratio.

The charge of gas and air was induced during part of the suction stroke and then it was ignited by an electric spark. The combustion of gas caused rise in pressure and temperature of mixture and did work on the piston during remaining part of the stroke. The gases after expansion were discharged to the atmosphere during return stroke. The P-V diagram fir Lenoir Engine is shown below:

3.      Otto-Langen Free Piston Engine:

Developed in 1866, it also consists of piston and cylinder arrangement but piston was not connected to any crankshaft and was free to move vertically outward during expansion stroke. As the explosion of gas and air takes place, the pressure and temperature of the mixture increases and piston is pushed upward. After expansion stroke, mixture is cooled and piston comes down with gravity causing downward stroke. The piston rod is connected to the flywheel by a ratchet and rack and pinion device. During downward stroke, the piston opens the sliding type exhaust valve and allows the burnt gases to go to atmosphere. The contact between the flame and mixture in the cylinder was provided with the help of an eccentric driven valve. The arrangement of engine is shown in the figure below:

4.      Four-stroke Otto-Engine

Otto developed a four stroke engine commonly known as suction, compression, power and exhaust. He used gas as a fuel and compression ratio was hardly 3. All the spark ignition (SI) engines operates on the same principle of Otto-cycle gas engine. The development of Otto engine is considered as an epoch making event in the history of IC engines. The development of this engine founded the IC engine technology and is still used today as a base for design.

5.      Brayton Engine

It is constant pressure combustion and complete expansion engine. It has two cylinders, one is used to compress the air and other is used to expand the high pressure, high temperature gases upto atmospheric pressure.

When the oil is used as fuel, the fuel is injected in the high pressure air coming from the compressor and heated higher pressure gases are expanded in the expansion cylinder known as engine. An ignition flame was supported mixture bypass and flame suppression grid prevented the flame from flashing back into receiver.

The arrangement of this engine is shown in figure:

6.      Atkinson Engine

It uses a short stroke for suction and compression and a long stroke for expansion and exhaust as shown in figure on P-V diagram. Atkinson used a single cylinder, as against two cylinders in Brayton engine. But the linkage mechanism was very complicated and because of that mechanical efficiency was considerably low. A constant volume gas turbine was also operated on this cycle which has become presently obsolete.

7.      Diesel Engine

It was developed in 1892 by Rudolf Diesel. He purposed to inject the liquid fuel in a compressed air at the end of compression. The temperature of compressed air was sufficient to burn the injected fuel. Therefore, these engines are commonly known as Compression Ignition (CI) engines. Two stroke and four stroke with airless injection are commonly used in different fields.

Classification of IC Engines

The internal combustion engines are usually classified on the basis of cylinder arrangement, cycle of operation, type of fuel used, method of charging the engine cylinder, type of ignition and type of cooling.

a.       Classification as per cylinder arrangement

·         Inline engine

·         V-type engine

·         Radial engine

·         Opposed piston engine

·         Opposed cylinder engine

·         Delta type

b.      Classification as per number of strokes

·         Two stroke

·         Four stroke

c.       Classification as per the type of fuel uses

·         Petrol engine

·         Diesel engine

d.      Classification as per the cooling system used

·         Air cooled engines

·         Water cooled engines

e.       Classification as per the thermodynamic cycle used

·         Otto cycle

·         Diesel cycle

·         Dual cycle

·         Brayton cycle

YV Nitesh

12^th Jan 2019