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4 ENGINEERING THERMODYNAMICS

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1.3. Internal Combustion Engines

1.3.1. Heat engines

Any type of engine or machine which derives heat energy from the combustion of fuel or

any other source and converts this energy into mechanical work is termed as a heat engine.

Heat engines may be classified into two main classes as follows :

1. External Combustion Engine.


2. Internal Combustion Engine.


3. External Combustion Engines (E.C. Engines)
   In this case, combustion of fuel takes place outside the cylinder as in case of steam engines
   where the heat of combustion is employed to generate steam which is used to move a piston in a
   cylinder. Other examples of external combustion engines are hot air engines, steam turbine and
   closed cycle gas turbine. These engines are generally needed for driving locomotives, ships, gen-
   eration of electric power etc.


4. Internal Combustion Engines (I.C. Engines)
   In this case combustion of the fuel with oxygen of the air occurs within the cylinder of the
   engine. The internal combustion engines group includes engines employing mixtures of combusti-
   ble gases and air, known as gas engines, those using lighter liquid fuel or spirit known as petrol
   engines and those using heavier liquid fuels, known as oil compression ignition or diesel engines.

1.3.2. Development of I.C. engines

Many experimental engines were constructed around 1878. The first really successful engine

did not appear, however until 1879, when a German engineer Dr. Otto built his famous Otto gas

engine. The operating cycle of this engine was based upon principles first laid down in 1860 by a

French engineer named Bea de Rochas. The majority of modern I.C. engines operate according to

these principles.

The development of the well known Diesel engine began about 1883 by Rudoff Diesel. Al-

though this differs in many important respects from the otto engine, the operating cycle of modern

high speed Diesel engines is thermodynamically very similar to the Otto cycle.

1.3.3. Different parts of I.C. engines

A cross-section of an air-cooled I.C. engines with principal parts is shown in Fig. 1.3.

A. Parts common to both petrol and diesel engines

1. Cylinder 2.Cylinder head 3.Piston


2. Piston rings 5.Gudgeon pin 6.Connecting rod


3. Crankshaft 8.Crank 9.Engine bearing


4. Crank case 11.Flywheel 12. Governor


5. Valves and valve operating mechanism.
   B. Parts for petrol engines only


6. Spark plugs 2.Carburettor 3. Fuel pump.
   C. Parts for Diesel engine only


7. Fuel pump. 2. Injector.