Engine exhaust, starting and stopping

DIESEL POWER PLANT

PRESENTATION BY

PARMAR PRIYANKA(11,01), DAVE NANDINI(08,07),

PATEL LEENA(10,03), PATEL AMISHA(09,404)

BARIA BHAVNA(11,04)

IT 5th SEM

PIET,WAGHODIA

Engine exhaust System

1> To discharge

engine exhaust to

the atmosphere outside the

building and

2>To reduce

pressure in exhaust line

And eliminate most of noise.

The function of exhaust System :

manifol

d

cylinders muffler exhaust

pipe

The componets of exhaust System : :

The exhaust manifold connects the engine cylinders exhaust

outlet to the exhaust pipe . the exhaust gases from the cylinders collect in the exhaust manifold & are conveyed to the atmosphere

through the exhaust pipe.

Working

* The exhaust pipe is provided with a muffler(silencer) to reduce pressure in exhaust line & eliminate most of noise

which may results if gases are discharged directly into the

atmosphere. The exhaust manifold is connected with exhaust pipe by one or two flexible expansion joints to allow for the expansion & to minimize the effect of engine vibration on system.

The temperature of exhaust gases leaving the engine is about 400 C when it works under full load conditions. Therefore large engine exhaust gases contains large amount of heat. This heat can be recovered and utilized in three manner as1 To heat the water which is supplied to the cylinder jackets 2 To generate low pressure steam in the water heat boiler which can be used for process heating3 To heat ventilating air which is supplied to the engine

Designing an exhaust System

1. The exhaust noise should be reduced to the desired level.

2 The exhaust should be discharged sufficiently height above the ground level in order to reduce the air pollution at ground level.

3 The expansion joints should be used to reduce the engine vibration on the exhaust system

4 The pressure loss in the exhaust system should be minimum.

5 There should be provision to recover the heat of exhaust gases to increase the efficiency of the plant.

Engine Starting by an auxiliary small engine

There are two engines:

1 Diesel engine that is main engine.

2 Small petrol engine.

Joining

Diesel engine and petrol engine are joined by clutch and gear arrangements.Small petrol engine can be easily started by means of manual operations

Working process:

First clutch is disengaged and petrol engine is started by hand operated system.

Then cluth gradually engaged and the power is transferred to diesel engine .

Automatic disengagement of clutch takes place after main engine has started.

The capacity of the starting petrol engine is just sufficient to overcome the friction of the main diesel engine.

Compressed air system

The compressed air system is generally used for starting large diesel engine employed for power plant . In this system compressed air a pressure of 17 bar is supplied from an air bottle to the engine cylinder either through a distributor or directly through inlet manifold .

In case of multicylinder engines, atleast one cylinder remains on the suction stroke.

When compressed air under the pressure enters cylinder, it pushes the cylinder thereby causing entire engine crankshaft assembly to rotate.Meanwhile the suction stroke of some other cylinder takes place and the compressed air again pushes the piston of this cylinder and causes the engine crank assembly to rotate.

Gradually the engine gains momentum and by turning on the fuel supply , engine will start running.

Starting by electric motor

The main advantages of electric starting are its simplicity and effectiveness. This system is used for small diesel engine.This system consist of an electric motor which is drives pinion which engages a gear toothed rim on engine .

A storage battery of 12 to 36 volts is used to supply power to an electric motor.

The first method from above as stopping fuel supply is the most commonly used for stopping diesel engine ,in which the fuel supply to injection pump is cut with the help of solenoid value as fig.

The solenoid valve is placed in the fuel supply line close to the inlet of the injection pumps. The valve needle has a megnatic head which is located inside a solenoid .When electric current is passed though the coil,a magnetic force is set up which moves the valve needle and allows fuel flow.

When hand operated switch button is the electric circuit is broken the needed come back and closes the valve and hence engone is stopped.

The motor draws a heavy current and is designed to engaged continuously for about 30 seconds only, after which it is required to cool off for a minutes or so, and then re-engaged. This is done till the engine starts up.

There is also arrangement for automatic disengagement after the engine has started.

When the engine is running a small d.c. generator on the engine serves to charge the engine serves to charge the battery otherwise small electric generator driven from the engine may be used.

Engine stopping system.

The engine should not be stopped abruptly . in order to stop engine, the speed should be decreased gradually until no power is delivered by generator .Then the engine is disconnected from the bus bars and is allowed to run idle for sometime.

1. Stopping fuel supply

2. keeping exhaust value open

3. shutting

of air supply

4. stopping

the action

of injection pump.

engine can be shut down with of the any one of the

following methods.

Thank you