Diesel Engine Power Plant Auxiliaries

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i. Diesel Engine Power Plant Auxiliaries

Auxiliary equipment consists of the following systems:

1. Fuel supply system. It consists of fuel tank for tank for the storage of fuel, fuel filters and pumps to transfer and inject the fuel. The fuel oil may be supplied at the plant site by trucks, rail, road ,tank ,tank ,cares etc.

2. Air intake and exhaust system .It consists of pipes for the supply of air and exhaust of the gases. Filters are provided to remove dust etc. from the incoming air. In the exhaust system silencer is provided to reduce the noise.

Filters may be of dry type(made up of cloth ,felt ,glass ,wool, etc. ) or oil bath type . In oil bath type of filters the air is swept over or through a bath of oil in order that the particles of dust get coated. The duties of air intake systems are as follows

i. To clean the air intake supply. ii. To silence the intake air.

iii. To supply air for super charging.

The intake must cause a minimum pressure loss to avoid reducing engine capacity and raising the specific fuel consumption. Filters must be cleaned periodically to prevent pressure loss from clogging. Silencers must be used on some systems to reduce high velocity air noise.

3. Cooling systems. This systems provides a proper amount of water circulation all around the engines to keep the temperature at reasonable level. Pumps are used to discharge the water inside and the hot water leaving the jacket is cooled in cooling in ponds or other devices and is recirculated again .

4. Lubricating systems. Lubrication is essential to reduce friction and wear of the rubbing parts. It includes lubrating oil tank, pumps, filters and lubricating oil cooler.

5. Starting systems. For initial starting of engine the various devices used are compressed airs, battery, electric motor or self starter.

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Starting procedure:

Actual process of starting the engine differs from engine to engine. Some common on steps foe starting the engine are as follows,

1. Before starting the engine it is desirable to check fuel system, lubricating system and cooling water supply.

2. 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 for possible leakage. The storage battery should be checked if electric motor is used for starting.

3. There should be no load on the engine.

4. 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.

5. The speed of the engine should be gradually increased till it, then connect the generator to the bus bars and finally increases the engine speed so that it takes up the desired load. Stopping the engine:

The engine should not be stopped abruptly. To stop the engine speed should be deceased 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.

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Starting aids: during cold weather to obtain quicker starting of the engine. Ethyl ether is mostly used as such aid. Glow plug forms a local hot spot thus initiating the combustion of fuel even if the compression temperature of air is sufficient.

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Advantages of Diesel Engine Power Plant:

The various advantages of the diesel engine power plants are as follows: 1. Plant layout is simple.

2. In this plant handling of fuel is easier. Small storage space for fuel is required, there is no refuse to be disposed off and oil needed can be easily transported.

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3. It can be located near load center.

4. A diesel engine extras more useful work from each heat unit than other types or I.C. engines. Therefore it becomes an attractive prime mover wherever first cost is written off and operating cost is important.

5. The plant can be quickly started and can pick up load in very short time. 6. There are no standby losses.

7. It does not require large amount of water for cooling.

8. The plant is smaller in size than steam power plant for the same capacity. 9. The operation of the plant is easy labour is needed to operate the plant. 10. Compared to steam power the plant is longer.

11. Diesel engines operate at higher thermal efficiency as compared to steam power plants.

Disadvantages

1.Diesel oil is costly.

2. The plant does not work satisfactory under overload conditions for long times. 3. Lubrication cost is high.

4.The capacity of plant is limited.

Applications of diesel engines plants:

1. They are quite suitable for mobile power generation and are widely used in

transportations systems consisting of rail roads, ships, automobiles and aeroplanes. 2. They can be used for electrical power generation in capacities from 100 to 5000 H.P. 3. They can be used as standby power plants.

4. They can be used as peak load plants for some other types of power plants.

5. Industrial concerns where power requirement are small say of the order of 500 kw, diesel power plants become more economical due to their higher overall efficiency.

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Four stroke cycle petrol (S.I) engine:

Construction:

A piston reciprocates inside the cylinder. The piston is connected to the crankshaft by means of a connecting rod and crank. The inlet and exhaust valves are mounted on the cylinder head. A spark plug is provided on the cylinder head. The fuel used is petrol. The events are given below,

(a) Suction stroke: (first stroke of the piston)

1. Piston moves down from top dead centre (T.D.C) to bottom dead centre (B.D.C). 2. Inlet valve is opened and the exhaust valve is closed.

3. Pressure inside the cylinder is reduced below the atmospheric pressure. 4. The mixture of air-fuel is sucked into the cylinder through the inlet valve. (b) Compression stroke:

1. Piston moves up from B.D.C to T.D.C.

2. Both inlet valve and exhaust valves are closed.

3. The air-fuel mixture in the cylinder is compressed. (The compression ratio vary from 5 to 8. The pressure at the end of compression is about 6 to 12 bar. The temperature at the end of compression is 250 to 350°C.)

Ignition:

When the piston reaches near T.D.C., a spark is produced by the spark plug. The compressed air-fuel mixture is ignited. The temperature (1800 - 2000°C) and the pressure (30 to 40 bar) of the burning gas (air fuel mixture) increases. ( C ) Working or power or expansion stroke: (Third stroke of the piston):

1. The burning gases expand rapidly. They exert an impulse (thrust or force) on the piston is pushed downward from T.D.C to B.D.C.

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2. This movement of the piston is converted into rotary motion of the crankshaft through connecting rod. Thus useful work is obtained.

3. Both inlet and exhaust valves are closed.

(d) Exhaust stroke (fourth at stroke of the piston): 1. Piston moves upward from B.D.C.

2. Exhaust valve is opened and the inlet valve is closed.

3. The burnt gases are forced out to the atmosphere through the exhaust valve. (some of the burnt gases stay in the clearance volume of the cylinder.)

4. The exhaust valve closes shortly after T.D.C.

5. The inlet valve opens slightly before T.D.C and the cylinder is ready to receive fresh charge to start a new cycle.

Thus in a four stroke engine, there is only one power and three idle strokes. The power stroke supplies the required momentum to carry out this internal and external work. Thus the engine is kept running. All the events (suction,

compression, power and exhaust) are completed in four strokes of the piston. Hence this is known as four stroke cycle engine.

Four stroke cycle Diesel (C.I) engine:

Construction:

A piston reciprocates inside the cylinder. The piston is connected to the crankshaft by means of a connecting rod and crank. The inlet and exhaust valves are mounted on the cylinder head. A Fuel injector is provided on the cylinder head. The fuel used is diesel. The events are given below,

(a) Suction stroke: (first stroke of the piston) 1. Piston moves from T.D.C to B.D.C.

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2. Inlet valve is opened and the exhaust valve is closed.

3. Pressure inside the cylinder is reduced below the atmospheric pressure.

4. Fresh air from the atmosphere is sucked into the engine cylinder through the air cleaner and inlet valve.

(b) Compression stroke: (second stroke of the piston): 1. Piston moves up from B.D.C to T.D.C.

2. Both inlet valve and exhaust valves are closed.

3. The air drawn during suction stroke is compressed to a high pressure and

temperature. (The compression ratio vary from 12 to 20. The pressure at the end of compression is about 35 to 40 bar. The temperature at the end of compression is 600 to 700°C.)

Ignition:

Nearly at the end of compression stroke, the fuel is injected into the engine cylinder in the form of fine spray. Ignition of air-fuel mixture takes place. The

burning of fresh fuel injected into the cylinder is due to the high pressure and temperature already developed in the cylinder during the compression stroke. ( C ) Working or power or expansion stroke: (Third stroke of the piston): 1. The burning gases (products of combustion) expand rapidly.

2. The burning gases push the piston to move downward from T.D.C to B.D.C. 3. This movement of the piston is converted into rotary motion of the crankshaft

through connecting rod. Thus useful work is obtained. 4. Both inlet and exhaust valves are closed.

(d) Exhaust stroke (fourth at stroke of the piston): 1. Piston moves upward from B.D.C. to T.D.C.

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2. Exhaust valve is opened and the inlet valve is closed.

3. The burnt gases are forced out to the atmosphere through the exhaust valve. (some of the burnt gases stay in the clearance volume of the cylinder.)

4. The exhaust valve closes shortly after T.D.C.

5. The inlet valve opens slightly before T.D.C and the cylinder is ready to receive fresh charge to start a new cycle.

Fuel supply system in diesel (C.I) engines:

In diesel engines, fresh air is draw into the engine cylinder during the suction store. This air is compressed to a very high pressure. The temperature of air also increased to a higher value to ignite the fuel injected into the cylinder. At the end of

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