Spark and Compression Ignition Engines.pptx

Farm Power and Machinary

1. SPARK AND COMPRESSION IGNITION ENGINES

2. The internal combustion engines are classified based on method of ignition of the fuel in the engine cylinder: Spark ignition engine (petrol engine ) and Compression ignition engine (diesel engine)

3. Spark ignition engine (Petrol engine) In this type of engine, a device called carburetor , which atomizes and mixes fuel with air in correct proportion and send the mixture to the engine cylinder during the suction stroke. Some times these engines are also regarded as carburetor type engine. It is an engine designed to convert chemical energy of heavier fuel into mechanical energy. The injected fuel is ignited by the heat of the air which is compressed by the piston within the cylinder.

4. Compression ignition engine (Diesel engine ) In compression ignition engines only air is drawn into the cylinder instead of mixture of air and fuel as in carburetor type engine. Compression of the air during the compression stroke makes the charge very hot, and increasing pressure and temperature. At the end of the compression stroke, diesel fuel is injected into the cylinder in atomised form through an injector, which ignites in the engine cylinder, causing rise in pressure which forces the piston to move downwards.

5. The basic elements of CI engine are same as that of spark ignition engine but the method of fuel introduction and ignition are different to a great extent. The engine has high compression ratio hence the air in the cylinder attains a very high temperature and pressure at the end of the compression stroke. At the end of the compression stroke, the fuel is sprayed into the cylinder through an atomizer (injectors).

6. The cylinder contains air at high pressure and temperature; hence the fuel begins to burn as soon as the fuel reaches the cylinder in atomised form. Such engines are called compression ignition engines because the ignition of fuel takes place due to heat of compression. CI engine is equipped with fuel injection pump and injectors. The injectors project into the combustion space of the engine.

7. Difference between Compression and Spark ignition engine

8. COOLING SYSTEM

9. Fuel is burnt inside the cylinder of an internal combustion engine to produce power and hence large amount of heat is produced inside the engine cylinder. This raises the temperature of the cylinder, piston and valves. The temperature may reach 1600 ᵒ C, which is above the melting point of the engine parts in contact. Because of heat the lubricating oil is also gets oxidized. So the cooling system is necessary for the engine to remove the excess heat from the engine block and to maintain the temperature of the components within the limit.

10. It is estimated that about 40% of the total heat produced in the engine cylinder is passed to the atmosphere by the exhaust gases, 30% is removed by cooling system and only about 30% is used to produce useful power. For satisfactory performance of the engine, neither overheating nor over-cooling is desirable. Experiments have shown that best operating temperature of Internal combustion engine lies between 60°C to 93°C, depending upon types of engines and load conditions.

11. Effect of high temperature in the engine Cylinder and piston may expand to such an extent that the piston would seize in the cylinder and stop the engine. Lubricating quality of the oil inside the cylinder would be reduced due to high temperature and resulting poor sucking of air in the cylinder. Pre-ignition of fuel mixture would take place and cause engine knocking as well as loss of power.

12. Purpose of cooling The main purpose of cooling are : To maintain optimum temperature of engine for efficient operation under all conditions. To remove excess heat for protection of engine components like cylinder, cylinder head, piston, piston rings and valves. To maintain the lubricating property of the oil inside the engine cylinder for normal functioning of the engine.