ENGINE STARTING METHODS
Spark ignition engines are used mainly in smaller size where compression ratio to be our come in cranking is only 5 to 7. Hand and electric motor (6 - 12 V, DC) cranking are practical. Diesel engines are difficult to be started by hand cranking because of high compression required and therefore mechanical cranking system is used.
The various methods used for the starting of diesel engine are as follows:
Compressed Air System: Compressed air system is used to start large diesel engines. In this system compressed air at a pressure of about 20 kg per sq. cm is supplied from an air bottle the engine an inlet valve through the distributor or through inlet manifold.
Electric Starting: Electric starting arrangement consists of an electric motor which a drives pinion which engages a toothed 11 on engine flywheel. Electric power supply for the motor is made available by a small electric generator driven from the engine in case of small plants a storage battery of 12 to 36 volts is used to supply power to the electric motor.
The electric motor disengages automatically after the engine has started. The advantages of electric starting are its simplicity and effectiveness.
Starting by an Auxiliary Engine: In this method a small petrol engine is connected to the main engine through clutch and gear arrangements. Firstly, the clutch is disengaged and petrol engine is started by hand. Then clutch is gradually engaged and the main engine is cranked for starting. Automatic disengagement of clutch takes place after the main engine has started.
STARTING PROCEDURE
Actual process of starting the engine differs from engine to engine. Some common steps for starting the engine are as follows:
Before starting the engine it is desirable to check fuel system, lubricating system and cooling water supply.
Depending upon the method of starting a check for the same is essential. If air starting is used the pressure of air should be checked and also the air system should be checked for possible leakage. The storage battery should be checked if electric motor is used for starting.
There should be no load on the engine.
Crank the engine and run it at slow speed for a few minutes and again check the working of various systems such as fuel, lubricating oil system etc.
The speed of the engine should be gradually increased till it synchronizes with the bus bars. Then connect the generator to the bus and finally increase the engine speed so that it takes up desired load.
STOPPING THE ENGINE
The engine should not be stopped abruptly. Top stop the engine the speed should be decreased gradually until no power is delivered by the alternator. Then the engine is disconnected from the bus bars and is allowed to run idle for some time.
STARTING AIDS
Starting aids may be used during cold weather to obtain quicker starting of the engine. Ethyl ether is mostly used as such aid. Glow plugs another starting aid. Glow plug forms a local hot spot thus imitating the combustion of fuel even if the compression temperature of air in sufficient.
FUEL SUPPLY
The fuels used in I.C. engines are in liquid form. They HIP preferred because of their high calorific value and case of storage and handling. The storage of oil fuel is simpler than the solid I n. I the amount of fuel to be stored depends upon the service hour’s unit vary for different installations. Bulk storage and engine day I hold the engine fuel. The fuel delivered to the power plant is received in storage tanks. Pumps draw the oil from storage tanks and supply it is the smaller day tanks from where the oil is supplied to the engine as shown in figure.
The fuel oil used should be free from impurities. Efforts should he made to prevent contamination of the fuel. An important step is to reduce the number of times the fuel is handled. Greater amount OF impurities settle down in the storage tank and remaining impurities are removed by passing the oil through filters. Storage tank may be located above the ground or underground. But underground storage tanks are preferred. It is provided with coils, heated by steam or hot water to reduce for viscosity and to lower the pumping cost. Main hole is provided FIN internal access and repair. Vent pipe is provided to allow the tank to breathe as it is filled or emptied. Level indicator measures the quantity of oil in the tank, and an overflow line is provided to control the quantity of oil.
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