Thermo-II Lab Manual OBE - 1-6 PDF

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LAB MANUALThermodynamics-IIME-212LDepartment of Mechanical EngineeringUniversity of Engineering and Technology,LahoreLab session:To determine the brake power, fuel consumption, specificfuel consumption and air to fuel ratio of Stuart DieselEngine.Figure 1: Stuart Diesel Engine####### 1 Theory:######...

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LAB MANUAL

Thermodynamics-II ME-212L

Department of Mechanical Engineering University of Engineering and Technology, Lahore

Lab session:01

To determine the brake power, fuel consumption, specific fuel consumption and air to fuel ratio of Stuart Diesel Engine.

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LAB SESSION NO: 1 1.1 Objective: To determine the brake power, fuel consumption, specific fuel consumption and air to fuel ratio of Stuart Diesel Engine.

1.2 Apparatus: Stuart Diesel Engine, tachometer, electrical dynamometer, stop watch etc.

1.3 Consumables: Diesel fuel

1.4 Engine Description: The description of the engine specifications is given as: No. of stokes = 02 No. of cylinders = 02 Engine configuration = vertical type Maximum Brake Horse Power (BHP) = 12hp Maximum speed = 2000rpm

Equipped with D.C electrical dynamometer Diagram:

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Figure 1.1: Stuart Diesel Engine

1.5 Theory: 1.5.1 Engine: Engine is a device that converts chemical energy of fuel (heat energy) to the mechanical energy.

1.5.2 Types of engines: Basically, there are two types of engines. Spark ignition engine (SI engine) Compression ignition engine (CI engine)

Spark ignition engine (SI engine): Petroleum engines are spark ignition engines. In spark ignition engine there is a spark plug that ignites air fuel mixture coming from the carburettor. In these engines the carburettor is the part of engine and it mixes air and fuel. Then in compression this mixture is compressed and spark plug ignites high pressure mixture through a spark.

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Figure 1.2:spark ignition engine

Compression ignition engine (CI engine): Diesel engines are basically compression ignition engines, and, in these engines, there is no need of spark plug rather the air is compressed and then the fuel is injected. In diesel engines, when the fuel is injected in the compressed air then this mixture starts igniting without initiating it through any kind of spark plug.

Figure 1.3:compression ignition engine

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Differences between petrol and diesel engines: Diesel engine 1. No spark plug is needed to start the ignition. Means it is a compression ignition engine. 2. The pressure at the end of the compression is almost 35 bar. 3. In diesel engines air is compressed first and then the diesel is injected through fuel injector. 4. Its compression ratio is almost 15 to 25. 5. Its efficiency is 25 to 30%.

Petrol engine 1. There is a spark plug for ignition, means it is a spark ignition engine. 2. The pressure at the end of compression is almost 10 bar. 3. In petrol engines, first air and fuel are mixed through the carburetor and then compressed in cylinder. 4. Its compression ratio is almost 6 to 10. 5. Its efficiency is almost 35 to 40 %

1.6 Procedure: 

Start the engine using D.C machine which acts as a starting motor as well as dynamometer. Verify that air and water circuits are running. Determine the engine speed with the help of tachometer. Note down the values of voltage and current with the help of voltmeter and ammeter. Take time for 25ml fuel consumption with the help of stop watch in seconds. Now from these values determine the brake power (BP), fuel consumption (FC), specific fuel consumption (SFC) and air to fuel ratio (AFR) by using the formulas as given in the observations and calculations.

    

1.7 Observations and calculations: Observations: Generator efficiency =

ηg

= 85%

Swept volume per cylinder = 250cc Density of diesel fuel = ρf

= 778 kg/m3

Diameter of orifice = d = 38.07mm

Brake power: When engine produces energy, then energy provided to crankshaft which is known as brake power of the engine. The generator efficiency can be given as η g=

VI BP

Where

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V = Voltage as read from the electrical dynamometer I = Current as read from the electrical dynamometer η g = Efficiency of the generator BP = Brake power From above relation we can find the value of brake power BP is: BP=

VI ηg

kW

Fuel consumption: Fuel consumption of any fuel can be defined as its consumption in kg per unit time. It can be given as m ´ f=

ρ f ⋅V t

kg/h

f

Where t = time for 25 litre fuel

Specific fuel consumption: It is the ratio of the fuel consumption to the break power. Means for an efficient engine this ratio should be small i.e. for a small fuel consumption the brake power should be large. It can be given as: SFC =

fuel consumtion B.P

Air to fuel ratio: Air to fuel ratio can be given as ´a A =m ´ F mf Where, m ´ f=

ρ f ⋅V t

Where, t = time for 25 litre fuel

How to find mass flow rate of air ( m´ a ¿ : The mass flow rate of the air can be given as: 6|Page

f

(kg/kWh)

´a mass flow rate of air ¿ m

= A ⋅V a . ρ a

Where A = area of orifice =

π 2 ⋅d 4

Where, d = diameter of orifice = 38.07mm The density of the air can be given as: ρ a=

Pa RT a

For air: R = specific gas constant = 0.287 kJ / kg K Ambient pressure = Pa=¿

1.01325 bar

Ambient temperature = T a=¿ 290.16 K NOTE: The values of the pressure and temperature depend on the laboratory conditions. However, it is a usual approximation to take the density of the air to be 1.2 kg/ m 3 . The velocity of the air can be given as: Velocity of air = V a

=

0.2

√

2 ΔP ρa

Where, ΔP= Δh (0.249 kpa )

Description of Δh : Δh

is the height of water in inches from manometer

29.92 inch of Hg = 101.325 kpa 29.92 × 13.6 inch of water = 101325 Pa 1 inch of water =

101325 =249 Pa 29 ⋅92 ×13.6

Therefore, 1 inch from water = 249 Pa For example, Δh

= 3 inches of water, the equivalent pressure would be:

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ΔP

= 3 × 249 = 0.747 kPa

Volumetric efficiency: It is the ratio of the volume of air entering ( V a ¿ to the volume of the gases leaving ( V s ¿ the engine. It can be given as: ηv =

V´ a V´ s

Where V´ a=

m ´a ρa

For a two-stroke engine: Swept volume per second, V´ s=swept volume per cycle × no. of cycles × no. of cylinders N π 2 V´ s= d × L × × n 60 4 Where n = no. of the cylinders, n = 2 Swept volume per cycle,

π 2 d × L=250 cc per cylinder 4

Torque: The torque provided by the engine can be given as:

Ƭ=

BP ×60 2π ×N

Thermal Efficiency: Thermal efficiency of the engine can be given as:

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BP ×100 m ´ f×C.V

ηth =

1.8 Sample Calculations: Table: Table 1:observation and calculation No of Obs.

N

V

Rpm

(V)

I

(A)

BP

kW

Time for 25 ml fuel t

mf FC X 10-4

sec

kg/sec

SFC

∆h

kg/kW h

in. of H2O

2 3 4

1.9 Graphs: Draw graph between rpm and B.P. Draw graph between rpm and S.F.C. Draw graph between rpm and volumetric efficiency. Draw graph between rpm and torque. Draw graph between rpm and thermal efficiency.

1.10 Discussion:

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Va

m ´a 10-3

1

    

∆P kPa

m/s

kg/sec

x

A F

ƞvol

ƞth

Torque Ƭ

%

%

Nm

Lab session:02

To draw the heat balance sheet of Ruston Diesel Engine

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Lab Session: 02 2.1 Objective To draw the heat balance sheet of Ruston Diesel Engine

2.2 Apparatus Ruston diesel engine, tachometer, dynamometer, stopwatch, diesel fuel.

2.3 Engine Specifications       

Number of strokes = 4 No of cylinders = 4 Engine configuration = Vertical type Maximum BHP = Maximum speed = 2000 rpm Stroke length = Diameter of bore =

2.4 Procedure 1. 2. 3. 4. 5.

Manually, start the engine by rotating the crankshaft. Verify that air and water circuits are running. Determine the engine speed with the help of tachometer. Take time for 25 ml fuel from fuel metering system by help of stopwatch in seconds. Take time for 2.25 liters of water in seconds in a gallon.

2.5 Theory A heat balance sheet is an account of heat supplied and heat utilized in various ways in the system. Necessary information concerning the performance of the engine is obtained from the heat balance. The heat balance is generally done on second basis or minute basis or hour basis. It is generally a practice to represent the heat distribution as percentage of heat supplied. Such a distribution is known as heat balance sheet. The main components of heat balance are;  Heat equivalent to effective work on the engine.  Heat rejected to the cooling medium.  Heat carried away from the engine with exhaust gases.  Unaccounted loses. The unaccounted loses are calculated as;

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Unaccounted loses = Heat supplied – (Brake power + Heat loss in cooling + Heat loss in exhaust)

2.6 Observations and Calculations Observations Heat supplied = ṁf x L.C.V Lower calorific value of fuel = Qnet, v = 44200 kJ / kg Vf = 25ml = 25 x 10-6 m3 Vf = Vf / t ṁf = Vf x ρf (ρf = 778 kg/m3)

Brake power =

VI η

Generator efficiency = ηg = 80% V = Voltage I = Current Heat supplied to the cooling water = Qw = ṁw x Cw x ∆T Vw = 2.25 L ρw = 1000 kg / m3 Mass flow rate of water = ṁw = Vw x ρw Volume flow rate of water = Vw = Vw /t Cw = Specific heat capacity of water = 4.2 kJ/kg.K ∆T = Temp. of coolant leaving the engine – Temp. of coolant entering the engine

Exhaust gases = QEG = ṁEG x CEG x ∆TEG Mass flow rate of exhaust gases = mass flow rate of fuel + mass flow rate of air 12 | P a g e

ṁEG = ṁf + ṁa Mass flow rate of air = ṁa = Va x ρa Volume flow rate of air = Va = A = Area of piston =

(ρa = 1.2 kg/m3)

N × A × L× n 120

π 2 d 4

L = Length of stroke N = Speed n = no. of cylinders CEG = 0.88 kJ/kg.K

The total heat supplied is distributed as; Heat supplied = Heat energy converted into brake power + Heat energy to cooling water + Heat energy in exhaust gases + unaccounted loses

2.7 Sample calculations:

Table 1: Exhaust N0 of obs

N rpm

V (V)

I (I)

Time For 25ml

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´ f × Time m (kg/s)

For 2.25L

´ w × Coolin m g

(kg/s)

Water

´ a × 1 gases m (kg/s)

Tavg ( C)

HS

BP

QW

QEG

QUH

kW

kW

kW

kW

kW

Fuel

Water

Outlet

(s)

(s)

Temp ( C)

1 2 3 4

2.8 Heat Balance Diagram:

2.9 Discussion:

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Lab session:03 To visualize the combustion behaviour of E20 fuelled transparent SI engine at various speed.

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Experiment No. 03 3.1 Objective: To visualize the combustion behaviour of E20 fuelled transparent SI engine at various speed.

3.2 Apparatus: 1. Transparent engine 2. Test bed with dynamometer 3. String 4. Compressor for air cooling

3.3 Figures: -

Figure 3.4: Burning of E20 in transparent engine

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Figure 3.5: Engine test bed with dynamometer

3.4 Consumables: 1. E20 fuel

3.5 Procedure: 1. 2. 3. 4. 5. 6. 7. 8. 9.

Setup the apparatus. Check the working of engine by starting it with generator. Turn on the air flow from cooling apparatus. Fill the fuel tank with gasoline fuel. Set appropriate value of load on engine test bed. Start the engine by pulling the string. Adjust the air fuel ratio by adjusting the adjustment valves. Visualize the combustion flame. Repeat the experiment by varying loads.

3.6 Observations: The observed combustion flames at different rpm are as under.

3.7

Discussion: -

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Lab session:04 To determine the thermal efficiency of steam boiler.

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Lab Session No. 4 4.1 Objective: To determine the thermal efficiency of steam boiler

4.2 Apparatus:  Boiler (OTSG) in STPP

Consumables:  Water  Kerosene oil

4.3 Related Theory 4.3.1 Rankine Cycle: The Rankine cycle is the fundamental operating cycle of all power plants where an operating fluid is continuously evaporated and condensed. The selection of operating fluid depends mainly on the available temperature range. Figure 6.1 shows the ideal Rankine cycle.

Figure 4.6:Rankine cycle

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Rankine cycle operates in the following steps:



1-2 Isobaric Heat Transfer. High pressure liquid enters the boiler from the feed pump (1) and is heated to the saturation temperature (2). Further addition of energy causes evaporation of the liquid until it is fully converted to saturated steam (3).



2-3 Isentropic Expansion. The vapor is expanded in the turbine, thus producing work which may be converted to electricity. In practice, the expansion is limited by the temperature of the cooling medium and by the erosion of the turbine blades by liquid entrainment in the vapor stream as the process moves further into the two-phase region. Exit vapor qualities should be greater than 90%.



3-4 Isobaric Heat Rejection . The vapor-liquid mixture leaving the turbine (4) is condensed at low pressure, usually in a surface condenser using cooling water. In well designed and maintained condensers, the pressure of the vapor is well below atmospheric pressure, approaching the saturation pressure of the operating fluid at the cooling water temperature.



4-1 Isentropic Compression. The pressure of the condensate is raised in the feed pump. Because of the low specific volume of liquids, the pump work is relatively small and often neglected in thermodynamic calculations.

4.3.2 Boiler: A boiler is a closed vessel in which water or other fluid is heated. The fluid does not necessarily boil. (In North America, the term "furnace" is normally used if the purpose is not to boil the fluid.) The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central heating, boiler-based power generation and cooking. The source of heat for a boiler is combustion of any of several fuels, such as wood, coal, oil, or natural gas. Electric steam boilers use resistance- or immersion type heating elements. Nuclear fission is also used as a heat source for generating steam, either 20 | P a g e

directly (BWR) or, in most cases, in specialized heat exchangers called "steam generators" (PWR). Heat recovery steam generators (HRSGs) use the heat rejected from other processes such as gas turbine.

4.3.2.1 Types of boiler: Fire Tube Boiler: Here, water partially fills a boiler barrel with a small volume left above to accommodate the steam (steam space). This is the type of boiler used in nearly all steam engines. The heat source is inside a furnace or firebox that has to be kept permanently surrounded by the water in order to maintain the temperature of the heating surface below the boiling point. The furnace can be situated at one end of a fire-tube which lengthens the path of the hot gases, thus augmenting the heating surface which can be further increased by making the gases reverse direction through a second parallel tube or a bundle of multiple tubes (two-pass or return flue boiler); alternatively, the gases may be taken along the sides and then beneath the boiler through flues (3-pass boiler). In case of a locomotive-type boiler, a boiler barrel extends from the firebox and the hot gases pass through a bundle of fire tubes inside the barrel which greatly increases the heating surface compared to a single tube and further improves heat transfer. Fire-tube boilers usually have a comparatively low rate of steam production, but high steam storage capacity. Fire-tube boilers mostly burn solid fuel but are readily adaptable to those of the liquid or gas variety. Fire-tube boilers may also be referred to as "scotch-marine" or "marine" type boilers. (Gottfried)

Figure 4.2: Fire tube boiler

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Water Tube Boiler: In this type, tubes filled with water are arranged inside a furnace in a number of possible configurations. Often the water tubes connect large drums, the lower ones containing water and the upper one steam and water; in other cases, such as a mono-tube boiler, water is circulated by a pump through a succession of coils. This type generally gives high steam production rates, but less storage capacity than the above. Water tube boilers can be designed to exploit any heat source and are generally preferred in high-pressure applications since the high-pressure water/steam is contained within small diameter pipes which can withstand the pressure with a thinner wall. These boilers are commonly constructed in place, roughly square in shape, and can be multiple stories tall.

Figure 4.3: Water tube Boiler

4.3.3 Steam Boiler Efficiency: The percentage of total heat exported by outlet steam in the total heat supplied by the fuel is called steam boiler efficiency.

It includes with thermal efficiency, combustion efficiency and fuel to steam efficiency. Steam boiler efficiency depends upon the size of boiler used. A typical efficiency of steam boiler

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is 80% to 88%. Actually, there are some losses occur like incomplete combustion, radiating loss occurs from steam boiler surrounding wall, defective combustion gas etc. Hence, efficiency of steam boiler gives this result.

4.4 Procedure: 1. Open water Supply valve. Turn main power ON. Open air purging valve. Open drain valve. 2. After total blow-off, close drain valve and air purging valve. 3. Open fuel valve and press feed water switch and then press combustion switch. 4. Steam pressure goes up and when it gets set value, combustion stops automatically. 5. Open main steam valve gradually. Note feed water inlet temperature from panel and note pressure of generated steam from the outlet pressure gauge. 6. Note the volume of feed water fed to the boiler and fuel consumed in specific time interval, from integral flow meter on control panel, to determine their volume flow rate.

4.5 Observations and Calculations ηT =

m´ s (hout −h¿ ) m´ f C .V

ms = mass flow rate of steam generated = ρw Vw /t mf = mass flow rate of fuel consumed = ρf Vf /t

1

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P1 bar

P2 bar

T2 ˚C

h2 kJ/kg

X

hout kJ/kg

Vw (L)

tw sec

Vf (L)

tf sec

ms kg/s

mf kg/s

Boiler efficiency

Time for Vf

Boiler fuel consumption

Time for Vw

Boiler water consumption

Boiler outlet enthalpy

Dryness fraction