Diesel power plant....For MEC 403 DAY BY BASHAR SIR

DIESEL ENGINE POWER PLANT

Contents:• Classification of I.C Engine.• Diesel Engine.• Advantage of Diesel Engine power plant.• Disadvantages of Diesel Engine power plant.

• Problem- 1 no.• Lubricant.• Function of Lubricant.• Types of Lubricant. • Properties of Lubricant.

DIESEL ENGINE POWER PLANTClassification of I.C.Engine: The I.C. (International Combustion)

engines may be classified in many ways, but the following are important from the subject point of view.

1. According to the type of fuel used: (a) Petrol Engine. (b) Diesel Engine. (c) Gas Engine. 2. According to the method of igniting the

fuel: (a)Spark ignition Engine (S.I) (b)Compression Ignition (C.I)

Engine 3. According to the number of strokes per

cycle: (a)Four stroke cycle Engine. (b)Two stroke cycle Engine.

DIESEL ENGINE POWER PLANT4. According to the number cycle of operation: (a)Otto cycle Engine. (b) Diesel cycle Engine. (c)Dual combustion cycle Engine.5. According to the speed of engine: (a) slow speed engine. (b) Medium speed Engine. (c)High speed Engine.6. According to the number of cylinder: (a)single cylinder Engine. (b) Multi-cylinder Engine.7. According to the cooling system: (a)Air cooled Engine. (b)Water cooled engine. (c) evaporative cooling Engine.

Working Principle of Diesel engine:


Sequence of operations in a cycle:a)Suction or charging stroke.b)Compression stroke.c)Expansion or working stroke.d)Exhaust stroke.

1. Suction or charging stroke: In this stroke, the inlet valve opens and pure air is sucked into the cylinder as the piston moves downwards from the top dead center (TDC). It continues till the piston reaches its bottom dead center (BDC) as shown in fig.

2. Compression stroke: In this stroke, both the valves are closed and the air is compressed as the piston moves upwards from BDC to TDC. AS a result of compression, pressure and temperature of the air increases considerably ( the actual value depends upon the compression ratio). This complete one revolution of the crank shaft. The compression stroke is shown in fig.


3. Expansion or working stroke: shortly before the piston reaches the TDC (during the compression stroke), fuel oil is injected in the form of fine spray into the engine cylinder, through the nozzle, known as fuel injection valve. At this moment, temperature of the compressed air is sufficiently high to ignite the fuel. It is suddenly increases the pressure and temperature of the products of combustion. The fuel oil is continuously injected for a function of a revolution. The fuel oil is assumed to be burnt at constant pressure. Due to increase pressure the piston is pushed down with a great force. The hot burnt gases expand due to high speed of the piston. During this expansion, some of the heat energy produced is transformed into mechanical work. It may be noted that during this working stroke, both the valves are closed and piston moves from T.D.C to B.D.C. 4. Exhaust stroke: In this stroke, the exhaust valve is open as the piston moves from BDC to TDC. This movement of the piston pushes out the products of combustion from the engine cylinder through the exhaust valve into the atmosphere. This completes the cycle and the engine cylinder is ready to such the fresh air again.


Actual indicator P-V Diagram for a four stroke Cycle Diesel Engine:

The actual indicator diagram for a four stroke cycle Diesel engine is shown in Fig (e). The suction stroke is shown by the line 1-2 which lies below the atmosphere pressure line. It is this pressure difference, which makes the fresh air to flow into the engine cylinder. The inlet valve offers some resistance to the incoming air. That is why the air can not enter suddenly into the engine cylinder.


As a result of this pressure in side the cylinder remains some whatbelow the atmospheric pressure during the suction stroke. The compression stroke is shown by the line 2-3 which shows that the inlet valves closes (IVC) a little beyond 2(i.e. BDC). Shortly before the end of compression stroke, the fuel valve opens (FVO) and the fuel is injected into the engine cylinder, and the fuel is ignited. The ignition suddenly increases volume and temperature of the products of combustion. But pressure, practically, remains constant as shown by the line 3-4. The expansion stroke is shown by the line 4-5, in which the exit valve opens (EVO) a little before 5 (i.e. BDC). The exhaust stroke is shown by the line 5-1, which lies the above the atmospheric pressure line. It is this pressure difference, which makes the burnt gases to flow out of the engine cylinder. The exit valve offers some resistance to the outgoing burnt gases. That is why the burnt gases cannot escape suddenly from the engine cylinder.


DIESEL ENGINE POWER PLANT And vantages 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. 3. It can be located near load center.4. A diesel engine extracts more useful work

from each heat unit than other types of I.C engines.

5. The plant can be quickly started and can pick up load in very short time.

6. There are no stand by 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

1. The operation of the plant is easy and less labor is needed to operate the plant.

2. Compared to steam power plant using steam turbine the life of diesel power plant is longer.

3. Diesel engine operate at higher thermal efficiency as compared to steam power plant.

Disadvantages of diesel engine power plant: The disadvantages of a diesel power plant are as follows-

4. Diesel oil is capacity.5. The plant does not work satisfactorily under

overload conditions for longer times. 6. Lubrication cost is high.7. The capacity of is limit

Diesel Power plant

DIESEL ENGINE POWER PLANTFormula:1. Indicated Horse power, IHP=

2. Break Horse power, BHP=

3. Indicated Thermal Efficient, ƞ=

4. Brake Thermal efficiency(over all efficiency), ƞb=

5. Mechanical Efficiency(%), ƞm= x 100

DIESEL ENGINE POWER PLANTWhere,Pm = Mean effective pressure (kg/cm2).L = Length of stroke (meters).A = Piston areas (cm2).N = speed (rpm).n = number of cylinders.K = 1 for two stroke engine. 2 for four stroke engine.T = Torque (kg-m).W = Weight of fuel supplied (kg/min).Cv = Calorific value of fuel oil (kcl/kg).J = joules equivent (= 427).

DIESEL ENGINE POWER PLANTProblem: 1 The following observations refer to trail on a four

stroke cycle gas engine;-Mean effective pressure = 7 kg/cm2

Fuel gas supplied = 0.24 m3/minCalorific value of the gas = 4500 kcl/m3

Stroke length = 50cmBore = 20cmSpeed = 300 rpmBrake load = 70 kgRadius of brake drum = 0.8 meter Determine of the

following-(a) I.H.P.(b) B.H.P.(c) Mechanical efficiency.(d) Thermal efficiency.(e) Indicated thermal.

DIESEL ENGINE POWER PLANTGiven data:Pm = 7 kg/cm2

W = 0.24 m3/minL = 50cm = 0.5 mD = 20cmN = 300 rpmBrake load = 70 kgRadius of brake drum =

0.8 m To find,(a) IHP = ?(b) BHP = ?(c) Ƞ m = ?(d) Ƞb = ?(e) Ƞ = ?

Here: A= πD2/4 = (π x 202 ) /4 = 314.16 cm2

T= Brake load x Radius of break drum.= 70 x 0.8= 56 kg-mn = 1 (For single cylinder)k = 2 (Four stoke engine)J = 427

I.H.P = (PmLANn) / (4500 x k) = (7 x 0.5 x 3.14 x 300 x 1) / (4500 x 2) = 36.65 (Answer)

Mechanical efficiency (%),

Ƞm = (B.H.P / I.H.P) X 100 = 23.46/36.65 = 64% (Answer). Thermal efficiency on B.H.P. (overall efficiency in %),

Ƞb = { (B.H.P. x 45000) / (w x Cv x J) } x 100 = { (23.46 x 4500) / (0.24 x 4500 x 427) } x 100 = 23% (Answer) Thermal efficiency on I.H.P. efficiency (%),

Ƞ = { (I.H.P. x 45000) / (w x Cv x J) } x 100 = { (36.65 X 4500) / (0.24 x 4500 x 427) } x 100 = 35.8% (Answer).


B.H.P. = (2πNT) / 4500 = (2 x π x 300 x 56) / (4500 x 2) = 23.46 (Answer).

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Problem: 2 In a gas engine the mean effective pressure (m.e.p) is 4.8

kg/cm² and the ratio of diameter of piston to stroke is . Calculate the size of four

stroke cycle gas engine if itruns at 250 P.P.M and its B.H.P. is 16. The mechanical

efficiency of the engine is 80%.

Solution. Mechanical efficiency, Let, D = Diameter of piston L =

Stroke

Where L is in meters and A (area) is in cm² Now

If D is in centimeters Now

And

208.016....

168.0....

PHIPHIPHI

PHBm

32


DIESEL ENGINE POWER PLANTLUBRICANT: Frictional forces causes wear and tear of rubbing part of the engine and there by the life of the engine is reduced. This requires that some substance should be introduced between the rubbing surface in order to decrease the frictional force between them. Such substance is called lubricant. The lubricant forms a thin film between the rubbing surfaces and prevents metal to contact.

The function of a lubricant are as follows: 1.It reduces wear and tear of various moving parts by

minimizing the force of friction and ensures smooth running of parts.

2.It helps the piston ring to seal the gases in the cylinder.

3.It removes the heat generated due to friction and keeps the parts cool.


Type of Lubricant: The various lubricants used in engine are types. such as:-

1. Liquid Lubricants: Lubricants are most commonly used .Liquid lubricants are of two 1.Liquid Lubricants: Lubricants are most commonly used .Liquid lubricants are of two types. Such as-

(a) Mineral oils. (b) Fatty oils. 2. Solid Lubricants: Graphite, white lead and mica are the solid turbid-cants.

3. Semi-sold lubricants: Grease is a semi-solid lubricants.

DIESEL ENGINE POWER PLANTProperties of a lubricant:

A good lubricant should possess the following properties; such as:-

1.It should not change its state with charge in temperature.

2.It should maintain a continuous films between the rubbing surfaces.

3.It should have high specific heat so that it can remove maximum amount of heat.

4.It heat be free from corrosive acids.5.It should be purified before it entre the engine.6.It should be chemically stable.7.It should be high resistance against corrosion.8.It should have high flash point.9.It should have low pour point.

Diesel power plant....For MEC 403 DAY BY BASHAR SIR

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