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