05-12-2012, 04:50 PM
Internal Combustion Engines
IC_Engine.ppt (Size: 1.96 MB / Downloads: 40)
Introduction of I.C. Engine
Heat Engines - A machine or device which derives heat from the combustion of fuel and converts part of this energy into mechanical work is called a heat engine. Heat engines may be classified into two main classes as follows:
1. External combustion engines
2. Internal combustion engines.
1. External Combustion Engines - In this case, combustion of fuel takes place outside the cylinder as in the 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.
Classification of I.C. Engines
The internal combustion engines may be classified in the following ways:
1. According to the type of fuel used
a) Petrol engines, b) Diesel engines, and c) Gas engines.
2. According to the method of igniting the fuel
a) Spark ignition engines, and b) Compression ignition
engines.
3. According to the number of strokes per cycle
a) Four stroke cycle engines, and b) Two stroke cycle
engines.
4. According to the cycle of operation
a) Otto cycle engines, b) Diesel cycle engines, and c) Dual
cycle engines.
Basic Idea of I.C. Engines
The basic idea of internal combustion engine is shown in Fig. (Basic idea of I.C. engine). The cylinder which is closed at one end is filled with a mixture of fuel and air. As the crankshaft turns it pushes cylinder. The piston is forced up and compresses the mixture in the top of the cylinder. The mixture is set alight and, as it burns, it creates a gas pressure on the piston, forcing it down the cylinder.
This motion is shown by arrow ‘1’. The piston pushes on the rod which pushes on the crank. The crank is given rotary (turning) motion as shown by the arrow ‘2’. The flywheel fitted on the end of the crankshaft stroes energy and keeps the crank turning steadily.
Constructional details of I.C. Engines
The details of the I.C. Engine parts are:
1. Cylinder - It is one of the most important part of the engine, in which the piston moves to and fro in order to develop power. The engine cylinder has to withstand a high pressure (more than 50 bar) and temperature (more than 2000 deg C). Thus the material for the engine cylinder should be such that it can retain sufficient strength at such a high pressure and temperature. For ordinary engines, the cylinder is made of ordinary cast iron. But for heavy duty engines, it is made of steel alloys or aluminum alloys.
Sometimes, a liner or sleeve is inserted into the cylinder, which can be replaced when worn out. As the material required for liner is comparatively small, it cab be made of alloy cast iron having long life and sufficient resistance to rapid wear and tear to the fast moving reciprocating parts.