23124

22562
3 Hours / 70 Marks Seat No.

Instructions : (1) All Questions are compulsory.

(2) Illustrate your answers with neat sketches wherever necessary.
(3) Figures to the right indicate full marks.
(4) Assume suitable data, if necessary.
(5) Use of Non-programmable Electronic Pocket Calculator is permissible.
(6) Mobile Phone, Pager and any other Electronic Communication
devices are not permissible in Examination Hall.
(7) Use of steam tables, logarithmic, Mollier’s chart is permitted.

Marks

1. Attempt any FIVE : 10

(a) List the various methods to reduce the pollution in diesel engine.

(b) List the various performance parameters of I.C. engine.

(c) Classify the air-conditioning system.

(d) Represent Brayton cycle on P-V and T-S.

(e) Define :

(i) Compression Ratio

(ii) Air Standard Efficiency

(f) Define pressure ratio in air compressor.

(g) Define SEER & EER.

[1 of 4] P.T.O.
22562 [2 of 4]
2. Attempt any THREE : 12

(a) Represent Otto cycle on p-v & T-s diagram.

(b) Explain working of a storage type water cooler with a sketch.

(c) Represent Joule’s cycle on p-v & T-s diagram.

(d) Discuss in brief process of combustion in S.I. engines with a sketch.

3. Attempt any THREE : 12

(a) Explain with neat sketch the working of Domestic Refrigerator.

(b) Explain the terms B.S.F.C., M.P.F.I.

(c) Octane number is measure of knock resistance. Justify the statement.

(d) Give four classification of air compressor.

4. Attempt any THREE : 12

(a) Explain the working of closed cycle gas turbine.

(b) Explain the following terms :

(i) Isothermal efficiency

(ii) Volumetric efficiency w.r.t. air compressor.

(c) Draw the neat labelled valve timing diagram for four stroke petrol engine.

(d) State formulae to calculate TEWI & LCCP.

(e) A four stroke engine has piston diameter of 90 mm, stroke length 200 mm and
indicated mean effective pressure 4.5 bar. Engine produces 420 explosions per
minute. Determine the mechanical efficiency of the engine if power available
at the shaft of engine is 1.8 kW.
22562 [3 of 4]
5. Attempt any TWO : 12

(a) A petrol engine uses 0.272 kg of fuel per kW of brake power per hour, with
calorific value as 43961 kJ/kg. The mechanical efficiency is 80% and
compression ratio is 5.6. Calculate

(i) Brake thermal efficiency

(ii) Indicated thermal efficiency

(iii) Air standard efficiency

(b) A single stage air compressor deliver air at 5 bar. The suction temperature and
pressure is 20C and 1 bar, respectively, volume of air entering the
compressor is 2 m3/min. The index of compression is 1.2. Calculate
Isothermal efficiency of the compressor.

(c) 400 kg of fruits are supplied to a cold storage at 19 C. The cold storage is
maintained to the storage temperature of –5 C in 10 hours. The latent heat of
freezing is 105 kJ/kg and specific heat of fruit is 1.256 kJ/kg K. Find the
refrigeration capacity of the plant.

6. Attempt any TWO : 12

(a) Compare reciprocating and rotary air compressor (at least six points).

(b) Moist air at the rate of 20,000 m3/h (on a dry air basis) is blown through an
adiabatic humidifier,

Inlet conditions : DBT 30 C & RH 15%.

Exit conditions : DBT 25 C & WBT 20 C.

Determine the :

(i) Dew point

(ii) Rate of moisture addition to air stream.

P.T.O.
22562 [4 of 4]
(c) In a test of a four cylinder four stroke engine 75 mm bore and 100 mm stroke
the following results were obtained at full throttle at a particular constant
speed and with fixed setting of fuel supply of 6.0 kg/hr.

B.P. with all cylinder working = 15.6 kW

B.P. with cylinder No. 1 cutout = 11.1 kW

B.P. with cylinder No. 2 cutout = 11.03 kW

B.P. with cylinder No. 3 cutout = 11.88 kW

B.P. with cylinder No. 4 cutout = 10.66 kW

If C.V. of fuel is 83600 kJ/kg, calculate :

(1) Mechanical efficiency

(2) Indicated thermal efficiency

_______________
22232
22562
3 Hours / 70 Marks Seat No.

Instructions : (1) All Questions are compulsory.

(2) Answer each next main Question on a new page.

(3) Illustrate your answers with neat sketches wherever necessary.

(4) Figures to the right indicate full marks.

(5) Assume suitable data, if necessary.

(6) Use of Non-programmable Electronic Pocket Calculator is permissible.

(7) Mobile Phone, Pager and any other Electronic Communication

devices are not permissible in Examination Hall.

(8) Use of Steam tables, logarithmic, Mollier’s chart and

psychrometric chart is permitted.

Marks

1. Attempt any FIVE of the following : 10

(a) Define the terms ‘Swept Volume’ and ‘Clearance Volume’ for an I.C. Engine.

(b) Define one ton of refrigeration.

(c) Define BSFC.

(d) State any two applications of compressed air.

(e) State two applications of gas turbines.

(f) State two important differences between turbojet and turboprop engines.

(g) State two advantages of supercharging.

[1 of 4] P.T.O.
22562 [2 of 4]
2. Attempt any THREE of the following : 12

(a) Compare SI and CI engines on the basis of following points :

(i) Method of ignition

(ii) Fuel used

(iii) Compression ratio

(iv) Noise and Vibrations

(b) Explain the working of catalytic convertor with neat sketch.

(c) Define the terms “volumetric efficiency” and “isothermal efficiency” for air
compressor.

(d) Represent Brayton cycle on P-V and T-S diagrams. Name the processes.

3. Attempt any THREE of the following : 12

(a) Represent Otto cycle and Diesel cycle on P-V and T-S diagrams.

(b) State the purpose of conducting Morse Test. Explain its procedure.

(c) Define DBT, WBT, Relative humidity and Specific humidity.

(d) Differentiate between two stroke and four stroke I.C. engines. (Any Four
Points)

4. Attempt any THREE of the following : 12

(a) Draw the neat sketch of Common Rail Direct Injection (CRDI) system. Label
all parts.

(b) Name any four sensors used in I.C. engines and state their functions.

(c) Draw the neat sketch of ice plant. Label all the components.

(d) Explain working of centrifugal compressor with neat sketch.

(e) Differentiate between open cycle and closed cycle gas turbine.
22562 [3 of 4]
5. Attempt any TWO of the following : 12
(a) Following observations are recorded during a trial on four stroke diesel engine :
Fuel supplied = 0.1 kg/min.
Calorific value of fuel : 41,840 kJ/kg
Engine speed : 400 rpm
Effective diameter of brake drum = 1 m
Net load on the brake drum = 1000 N
Mass flow rate of cooling water = 10 kg/min
Rise in cooling water temperature = 25 ºC
Air supplied : 6 kg/min
Exhaust gas temperature : 200 ºC
Specific heat of water : 4.186 kJ/kg ºk
Specific heat of exhaust gas : 1 kJ/kg ºk
Room temperature = 30 ºC
Prepare heat balance sheet on minute basis.
(b) A single stage air compressor delivers air at 5 bar. Suction temperature is
20 ºC. Suction pressure is 1 bar. The volume of air entering into compressor is
3 m3/min. The index of compression is 1.2. Calculate power required and
isothermal efficiency.
(c) A refrigeration system works on vapour compression cycle. Enthalpies at
various points are given below :
Compressor inlet : 1460 kJ/kg
Compressor outlet : 1796 kJ/kg.
Inlet to expansion valve : 322 kJ/kg.
Calculate : (i) COP (ii) Power required for one kg of refrigerant circulated per
min.
The refrigerant is superheated by 15 ºC before it enters the compressor and
subcooled by 3 ºC before expansion. Sketch the cycle on P-H and T-S
diagrams.

P.T.O.
22562 [4 of 4]
6. Attempt any TWO of the following : 12
(a) A single cylinder four stroke diesel engine gave the following results :
Speed of the engine : 400 rpm
Load on the brake : 370 N
Diameter of the brake Drum : 1.2 m
Fuel consumption : 2.8 kg/hr
Calorific value of fuel : 41,800 kJ/kg
Cylinder diameter : 160 mm
Piston stroke : 200 mm
Calculate : (i) Brake Power (ii) bsfc (iii) Brake thermal efficiency

(b) It is desired to compress 16 m3 of air per minute from 1 bar to 10.5 bar.
Calculate minimum power required to drive the compressor with two stage
compression and compare it with power required for single stage compressor.
Assume the value of index of compression 1.35 in both cases. Also, assume
the condition for maximum efficiency.
(c) With the help of psychrometric chart find following properties of air at 25 ºC
DBT and 50% relative humidity :
(i) Dew point temperature
(ii) Wet bulb temperature
(iii) Specific volume of air
(iv) Enthalpy of air
(v) Specific humidity of air
Draw psychrometric chart showing all above properties.

_______________
21222
22562
3 Hours / 70 Marks Seat No.
15 minutes extra for each hour

Instructions : (1) All Questions are compulsory.

(2) Answer each next main Question on a new page.
(3) Illustrate your answers with neat sketches wherever necessary.
(4) Figures to the right indicate full marks.
(5) Assume suitable data, if necessary.
(6) Use of Non-programmable Electronic Pocket Calculator is permissible.
(7) Mobile Phone, Pager and any other Electronic Communication
devices are not permissible in Examination Hall.
(8) Use of steam tables, logarithmic, Mollier’s chart is permitted.

Marks
1. Attempt any FIVE of the following : 10
(a) Define :
(i) Compression Ratio
(ii) Air standard Efficiency
(b) List the various methods to reduce the pollution in diesel engine.
(c) List the various performance parameters of I.C. engine.
(d) Define :
(i) Free Air Delivery (FAD)
(ii) Volumetric efficiency related to air compressor
(e) Represent Brayton cycle on P–V and T–S chart.
(f) Classify the gas turbines on the basis of
(i) Combustion Process
(ii) Path of working substance
(g) Classify the air-conditioning systems.

[1 of 4] P.T.O.
22562 [2 of 4]
2. Attempt any THREE of the following : 12
(a) Compare the SI engine with CI engine on following basis –
(i) Working cycle (ii) Ignition system
(iii) Compression ratio (iv) Applications
(b) List the polluting emissions in exhaust of I.C. engine. Explain their effect on
environment.
(c) Explain working of two stage reciprocating air-compressor with P–V diagram.
(d) Explain with neat sketch the working of turbojet engine.

3. Attempt any THREE of the following : 12

(a) Draw the actual and theoretical indicator diagram for 4 stroke engine. State
the reasons of change in diagram.
(b) Explain with neat sketch the CRDI system used in diesel engine, controlled by
ECU.
(c) “Octane number is measure of knock resistance.” Justify the statement.
(d) Represent vapour compression refrigeration cycle with subcooling on P–h and
T–S chart. Explain the effect of subcooling on system performance.

4. Attempt any THREE of the following : 12

(a) State the objectives and advantages of supercharging.
(b) Explain the procedure of fault finding in two wheelers with diagnostic tool.
(c) Compare the rotary compressor with reciprocating type air compressor on the
following basis.
(i) Delivery pressure
(ii) Discharge
(iii) Balancing & Vibration
(iv) Running Speed of compressor
(d) Draw label schematic diagram of liquid propellant system used in rockets.
List the points which differentiates this system from solid propellant system.
22562 [3 of 4]
(e) Plot the psychrometric chart and show the following processes on it :
(i) Sensible heating
(ii) Latent cooling
(iii) Latent heating
(iv) Sensible cooling
(v) Heating with humidification
(vi) Heating with dehumidification
(vii) Cooling with dehumidification
(viii) Cooling with humidification

5. Attempt any TWO of the following : 12

(a) Explain the methods to control the exhaust emissions of light motor vehicle to
achieve euro norms.
(b) Single acting two stage air compressor with complete intercooling delivers
6 kg/min of air at 16 bar. Assuming an intake at 1 bar and 15C. Compression
has index n = 1.3.
Calculate :
(i) Power required to drive the compressor
(ii) Isothermal efficiency
(iii) Free air delivered
(c) A refrigeration system using R-12 as refrigerant works on Vapour
compression cycle. Temperature in condenser and evaporator are 37C and
–18C respectively. Enthalpy of refrigerant after compression is 595.7 kJ/kg
and mass flow rate is 100 kg/hec. Find – (i) COP (ii) Capacity of plant in
tones of refrigeration (iii) Power required by compressor.
Show the process on P–h chart. Take the values from chart –
Temp. Pressure Sp. Volume Enthalpy Enthalpy Vapour
T C P bar  m3/kg liquid Hf. Hg kJ/kg.
– 18 1.6627 0.1030 402.28 565
37 9.0726 0.0203 455 589

P.T.O.
22562 [4 of 4]
6. Attempt any TWO of the following : 12
(a) In a test on single cylinder four stroke petrol engine, the following results are
obtained – Cylinder bore = 15 cm, length of stroke = 25 cm, Indicated mean
effective pressure = 7.353  105 N/cm2, Engine speed = 400 RPM, Brake
Torque = 225 N.m, Fuel consumption = 3 kg/hec., Calorific value of
fuel = 44200 kJ/kg.
Determine :
(i) Mechanical efficiency
(ii) Brake thermal efficiency
(iii) Specific fuel consumption of engine
(b) A single acting two stage compressor with complete intercooling delivers
5 kg/min of air at 15 bar. The conditions at intake are 1 bar and 15C. The
compression follow the law PV1.3 = C. Calculate the power required and the
isothermal efficiency, if the compressor run at 400 rpm speed.
(c) Draw the layout of ice plant. Name all important components of it and explain
its working in brief.
_______________
11920
22562
3 Hours / 70 Marks Seat No.

Instructions : (1) All Questions are compulsory.

(2) Illustrate your answers with neat sketches wherever necessary.
(3) Figures to the right indicate full marks.
(4) Assume suitable data, if necessary.
(5) Use of Non-programmable Electronic Pocket Calculator is permissible.
(6) Use of psychrometric chart is allowed.

Marks
1. Attempt any FIVE of the following : 10
(a) List diagnostic tools used in fault finding of MPFI engines.
(b) Define SEER & EER.
(c) State purpose of Selective Catalytic Reduction (SCR).
(d) Define Pressure Ratio in air compressors.
(e) List at least six components of a jet engine.
(f) List different liquid propellants used in rocket engines.
(g) State four objectives of supercharging.

2. Attempt any THREE of the following : 12

(a) Draw actual indicator diagram for 4 stroke petrol engine.
(b) Draw a typical graph indicating changes in pollutants level (HC, CO2 & CO)
with respect to changes in air fuel ratio.
(c) Describe in brief working of axial flow compressor with sketch.
(d) Explain in brief aero derivative & heavy frame engine. State their applications
separately.

3. Attempt any THREE of the following : 12

(a) List changes made by automobile manufactures in achieving BS VI norms in
diesel engines.
(b) Discuss in brief process of combustion in SI engines with a sketch.
(c) Explain working of a storage type water cooler with a sketch.
(d) In otto cycle compression ratio is 8. Calculate air standard efficiency. Will it
be grater than Carnot Cycle ? Justify your answer.

[1 of 2] P.T.O.
22562 [2 of 2]
4. Attempt any THREE of the following : 12
(a) Draw inline fuel injection pump. Name different components.
(b) With sketch, justify use of Variable Geometry Turbocharger as compared to
fixed geometry turbocharger.
(c) State formulae to calculate TEWI & LCCP.
(d) Draw PV diagram for working of two stage reciprocating air compressor
when inter-cooling in perfect and imperfect.
(e) Compare turbojet & turboprop engines (at least four parameters).

5. Attempt any TWO of the following : 12

(a) A two stroke cycle internal combustion engine has a mean effective pressure
of 5.8 bar. The speed of the engine is 940 rpm. If the diameter of piston and
stroke are 120 mm and 130 mm respectively, find the indicated power
developed and piston speed.
(b) A single acting reciprocating air compressor has cylinder diameter and stroke
of 201 mm & 301 mm respectively. The compressor sucks air at 1 bar and
27 C and delivers at 8 bar while running at 101 rpm. Find indicate power of
compressor, mass of air delivered by compressor per minute. Compression
follows law PV1.25 = C Take R = 287 J/kg K.
(c) In a typical refrigeration system refrigerating effect of 9.5 Tons of
refrigeration is expected. Enthalpy values of refrigerant per kg at various
locations are 185 kJ (compressor inlet), 206 kJ (compressor outlet), 70 kJ
(condenser exit). Assuming no under cooling & superheating find mass of
refrigerant per second required to be circulated. Also find COP of the system.

6. Attempt any TWO of the following : 12

(a) A 4 cylinder, 4 stroke petrol engine has 5 cm bore and 8 cm stroke. It was
tested at constant speed. Fuel consumption was 0.13 kg/min. Spark plugs for
four cylinders were cut one after other. Brake Power was measured and was
found as follows :
When all cylinders working = 16.25 kW, first cylinder cutoff = 11.55 kW,
second cylinder cutoff = 11.65 kW, third cylinder cutoff = 11.70 kW, fourth
cylinder cutoff = 11.50 kW. Find IP & Mechanical Efficiency.
(b) Compare reciprocating and rotary air compressor (at least six points).
(c) Expected room conditions are 20 C & 55% RH. Outdoor conditions are
39 C and RH 70%. Locate both points on psychrometric chart and find how
much enthalpy per kg of air and moisture content per kg of dry air need to be
changed to achieve room conditions. Draw skeleton of psychrometric chart
and show both points.
__________
 MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION
(Autonomous)
(ISO/IEC - 27001 - 2013 Certified)
__________________________________________________________________________________________________
WINTER – 19 EXAMINATION
Subject Name: Power Engg. & Refrigeration Model Answer Subject Code: 22562
Important Instructions to examiners:
1) The answers should be examined by key words and not as word-to-word as given in the model answer scheme.
2) The model answer and the answer written by candidate may vary but the examiner may try to assess the
understanding level of the candidate.
3) The language errors such as grammatical, spelling errors should not be given more Importance (Not applicable for
subject English and Communication Skills.
4) While assessing figures, examiner may give credit for principal components indicated in the figure. The figures
drawn by candidate and model answer may vary. The examiner may give credit for any equivalent figure drawn.
5) Credits may be given step wise for numerical problems. In some cases, the assumed constant values may vary and
there may be some difference in the candidate’s answers and model answer.
6) In case of some questions credit may be given by judgement on part of examiner of relevant answer based on
candidate’s understanding.
7) For programming language papers, credit may be given to any other program based on equivalent concept.

Q. Su Answer Marking
b
No. Q. Scheme
N.

Q.1 a) Following are the diagnostic tools used in fault finding of MPFI engines Any 4

(A) 1. Engine Code Readers 5. Scan Tool 2M

2. Compression Testers 6. Battery Tester

3. Spark Plug Testers 7. Power Probe III

4. Mechanic’s Stethoscope

b) SEER: Seasonal Energy Efficiency Ratio (SEER), is most commonly used to measure the efficiency 1M
of a central air conditioner. The higher the SEER, the more efficient the system OR It is the ratio
of cooling Capacity to energy consumed in watts-hours. each

EER: Energy Efficiency Ratio (EER) is a measure of how efficiently a cooling system will operate
when the outdoor temperature is at a specific level (95 degrees F). The higher the EER, the more
efficient the system. In technical terms,(Correction) OR It is the ratio of total capacity to the total
KW energy usage at specific humidity and temperature condition.

c) Purpose of Selective Catalytic Reduction (SCR) : 2M

1. It reduces Nox 75% to 90% Any 2

Point
2. Converts it in to molecular nitrogen and water vapor

3. It reduces HC emission up to 80%

4. It reduces PM emission 20 to 25%.

d) Compressor pressure ratio (CPR), is the ratio of the air total pressure exiting the compressor to 2M

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 MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION
(Autonomous)
(ISO/IEC - 27001 - 2013 Certified)
__________________________________________________________________________________________________
the air pressure entering the compressor. This number is always greater than 1.0.

e) Following are the components of jet engine: Any

1. Air intakes Six
2. Compressors
For 2M
3. Combustors
4. Turbines
5. Afterburners (reheat)
6. Nozzle
7. Bypass duct
8. Shaft
f) Following are the different liquid propellants used in rocket engines 2m

1. kerosene, Liquid oxygen and Liquid Hydrogen similar to kerosene ½M

2. Alcohol and its derivatives (Ethyl Alcohol) Each

3. hydrazine and its derivatives Any 4

Point
4. Hydrogen peroxide

5. liquid hydrogen

g) Following are the objectives of supercharging 2m

1. To compensate for loss of power due to high altitudes for air craft engines ½M

2. To obtain better performance from the existing engine Each

3. For a given weight and bulk of the engine, super charging increase power output. This is Any 2
important in air craft, marine and automotive engines where weight and space are Points
considered

4. Super charging is done to induct more amount of air into cylinder per unit times and
hence to burn more amount of fuel to increase power output

Page No: ____/ N

 MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION
(Autonomous)
(ISO/IEC - 27001 - 2013 Certified)
__________________________________________________________________________________________________
Q.2 a)

4M

Actual Indicator diagram for 4 stroke petrol engine

b) Graph indicating changes in pollutants level w.r.t air fuel ratio

4M

c) Axial flow compressor :

Working Principle: As the fluid enters and leaves in the axial direction, the centrifugal
component in the energy equation does not come into play. Here the compression is fully based
on diffusing action of the passages. 2M

The diffusing action in stator converts absolute kinetic head of the fluid into rise in pressure.
The relative kinetic head in the energy equation is a term that exists only because of the rotation
of the rotor.

The rotor reduces the kinetic head of the fluid and adds it to the absolute kinetic head of the
fluid i.e. the impact of the rotor on the fluid particles increases its velocity (absolute) and
thereby reduces the relative velocity between the fluid and the rotor.

In short increases the absolute velocity of the fluid and the stator converts this into pressure
rise.

Page No: ____/ N

 MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION
(Autonomous)
(ISO/IEC - 27001 - 2013 Certified)
__________________________________________________________________________________________________
2M

d)
Heavy frame industrial gas turbines compared to aero derivative gas turbines are usually slower
in speed, narrower in operating speed range, heavier, larger, have higher air flow, slower in 2M
start-up and need more time and spare parts for maintenance. Heavy frame industrial gas
turbines use hydrodynamic bearing.

Aero derivative gas turbines use anti-friction bearing. Advanced aircraft engine and space
technologies have been used to provide maintainable, flexible, light weight and compact aero
derivative gas turbines. The key to maintainability is the modular concept which provides for
removal of components and replacement without removing the gas turbine from its support
mounts.

The heavy frame industrial units, by contrast, require more amount of effort to remove and
replace components (especially combustor parts) and more effort to inspect or repair the
sections. The user should weigh needs and requirements against the variety of gas turbines
offered.
2M
Applications-

Traditionally, preference has been to place the aero derivative units in remotely located
applications (including offshore) and to place heavy frame industrial units in easily accessible
base-load applications. The heavy frame industrial gas turbines consume more fuel and more air
than the aero derivative units. They are exposed to a greater quantity of the contaminants in air
that cause corrosion.

Q.3 a) Following are Changes in automobile manufacturers in achieving BS6 norms of diesel engines Any

1. Reduction in HC emission by 45% Four

2. Reduction in NOX emission by 70% Changes

1M
3. Reduction in PM emission by 80%
each
4. Use of Lean NOX traps

5. Use selective catalytic reduction (SCR)

6. Use of Diesel particulate filter

7. Five times reduction in Sulpher %

Page No: ____/ N

 MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION
(Autonomous)
(ISO/IEC - 27001 - 2013 Certified)
__________________________________________________________________________________________________
8. OBD for all diesel vehicles

9. Real Driving Emission introduced in vehicles

10. Fumigation

11. Catalytic converter monitoring

12. Misfire detection

b) Combustion In S I Engine

Fig.

2M

According to Ricardo, There are three stages of combustion in SI Engine as shown in figure
above 1. Ignition lag stage 2. Flame propagation stage 3. After burning stage

1. Ignition lag stage:

There is a certain time interval between instant of spark and instant where there is a noticeable Stages
rise in pressure due to combustion. This time lag is called IGNITION LAG. 2M
2. Flame propagation stage:

Once the flame is formed at “b”, it should be self sustained and must be able to propagate through
the mixture. This is possible when the rate of heat generation by burning is greater than heat lost
by flame to surrounding. After the point “b”, the flame propagation is abnormally low at the
beginning as heat lost is more than heat generated.

3.After burning:

Combustion will not stop at point “c” but continue after attaining peak pressure and this
combustion is known as after burning. This generally happens when the rich mixture is supplied
to engine.

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 MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION
(Autonomous)
(ISO/IEC - 27001 - 2013 Certified)
__________________________________________________________________________________________________
c)

Fig.

2M

OR

Storage type Water Cooler

The storage type cooler has the evaporator coil soldered on to the walls of the storage tank
of the cooler, generally on to the outside surface of the walls. The tank could be of the galvanized
steel or stainless steel sheets. Water level is maintained in the tank by a float wall.

Push type water taps are generally provided for drawing cold water in both the types, to
minimize the wastage of refrigerated water. Thermostat controls the operation of the compressor
to maintain the water temperature at the desired level. The feeler bulb of the thermostat is
clamped on to the water coil just at its outlet end in the instantaneous cooler. In the storage type,
the bulb is kept immeresed in water in the tank or clamped to the wall of the storage tank on the
outside at a lower level, much below the lower most evaporator refrigerant tube soildered on to
the tank. 2M

Page No: ____/ N

 MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION
(Autonomous)
(ISO/IEC - 27001 - 2013 Certified)
__________________________________________________________________________________________________
d)

2M

No, the Otto cycle efficiency 56.47% will always be lower than Carnot cycle efficiency. 1M

Justification: Carnot theorem states that keeping operating conditions same, Carnot engine is
more efficient than any other engine. So, Otto cycle efficiency is lower than Carnot cycle
1M
efficiency.

Q.4 a)

Fig.

3M

Naming

1M

Inline Fuel Injection Pump

Page No: ____/ N

 MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION
(Autonomous)
(ISO/IEC - 27001 - 2013 Certified)
__________________________________________________________________________________________________
b)

Sketch

2M

Variable Geometry Turbocharger

Justification

Variable Turbine Geometry technology is the next generation in turbocharger technology where the turbo
uses variable vanes to control exhaust flow against the turbine blades. The problem with the fixed 2M
geometry turbocharger that big turbochargers do not work well at slow engine speeds, while small
turbochargers are fast to spool but run out of steam pretty quick.

A turbocharger equipped with Variable Turbine Geometry has little movable vanes which can direct
exhaust flow onto the turbine blades. The vane angles are adjusted via an actuator. The angles of the
vanes vary throughout the engine RPM range to optimize turbine behaviour.

c) TEWI (Total equivalent warming impact ) 2M

TEWI = GWP⋅ L ⋅ n + GWP⋅m⋅(1−α) + n ⋅ E ⋅ β (1)

where, GWP - Refrigerant Global Warming Potential (equivalent to CO2) [kg CO2/kg refrigerant]

L - Annual leakage rate [kg/year]

n - System operating life time [years]

m - Refrigerant charge [kg] α - Recycling factor [%]

E - Annual energy consumption [kWh/year]

β - CO2 emissions on energy generation [kg CO2/kWh]

2M
LCCP ( Life-cycle climate performance )

LCCP = TEWI + GWP (Indirect) [energy consumption expressed as CO2- eq emissions from chemical
production & transport, manufacturing components & vehicle assembly and end-of-life] + GWP (direct)
[chemical refrigerant emissions including atmospheric reaction products, manufacturing leakage, and
end-of- -life]

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d) 2M

each

e)

Any
four
points

1M

each

- Engine is noisy - Engine is less noisy

- Engine consist of Diffuser, - Engine consist of Diffuser, Compressor,

Compressor, Combustion Chamber,
Turbine, Nozzle. Combustion Chamber, Turbine, Nozzle with

Propeller

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Q.5 a)

Speed in terms of m/min Piston speed = 244.38 m/min

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b)

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c)

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Q.6 a)

b) Reciprocating compressor Rotary compressor

1. Compression of air takes place with help of 1. Compression of air takes place due to rotary Any
piston and cylinder arrangement with motion of blades.
Six
reciprocating motion of piston.
points
2. Delivery of air intermittent. 2. Delivery of air is continuous.
1M
3. Delivery pressure is high i.e. pressure ratio 3. Delivery pressure is low, i.e. pressure ratio is
is high. low. each
4. Flow rate of air is low. 4. Flow rate of air is high.

5. Speed of compressor is low because of 5. Speed of compressor is high because of

unbalanced forces. perfect balancing.
6. Reciprocating air compressor has more 6. Rotary air compressor has less number of
number of moving parts. moving part.
7. It needs proper lubrication and more 7. It required less lubrication and
maintenance. maintenance.

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8. Due to low speed of ration it can’t be 8. Rotary air compressor can be directly
directly coupled to prime mover but it coupled to prime mover.
requires reduction of speed.
9. It is used when small quantity of air at high 9. It is used where large quantity of air at
pressure is required. lower pressure is required.
10. Receiver Compulsory 10. Receiver not compulsory
11. Mechanical Efficiency Low 11. Mechanical Efficiency High
12. More Starting torque required 12. Less Starting torque required

c)

3
Marks
for
calculation

Skelton diagram -

3
Marks
for dig.

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WINTER – 2022 EXAMINATION
Model Answer

Subject Name: Power Engineering & Refrigeration Subject Code: 22562

Important Instructions to examiners: XXXXX
1) The answers should be examined by key words and not as word-to-word as given in the model answer
scheme.
2) The model answer and the answer written by candidate may vary but the examiner may try to assess the
understanding level of the candidate.
3) The language errors such as grammatical, spelling errors should not be given more Importance (Not
applicable for subject English and Communication Skills.
4) While assessing figures, examiner may give credit for principal components indicated in the figure. The
figures drawn by candidate and model answer may vary. The examiner may give credit for any equivalent
figure drawn.
5) Credits may be given step wise for numerical problems. In some cases, the assumed constant values
may vary and there may be some difference in the candidate’s answers and model answer.
6) In case of some questions credit may be given by judgement on part of examiner of relevant answer
based on candidate’s understanding.
7) For programming language papers, credit may be given to any other program based on equivalent
concept.
8) As per the policy decision of Maharashtra State Government, teaching in English/Marathi and Bilingual
(English + Marathi) medium is introduced at first year of AICTE diploma Programme from academic year
2021-2022. Hence if the students in first year (first and second semesters) write answers in Marathi or
bilingual language (English +Marathi), the Examiner shall consider the same and assess the answer
based on matching of concepts with model answer.

Q. Sub Answer Marking

No. Q. Scheme
N.

1. Attempt any FIVE of the following: 10

a) Define : i)Indicating Power ii) Octane Number 2 Marks

Sol. i) Indicated Power: The total power developed by combustion of fuel in the combustion 1 mark
chamber is called indicated power.

ii) Octane Number: a number that is used to measure the antiknock properties of a liquid
1 mark
motor fuel (such as gasoline)
b) 2 marks
Name the components used in Vapour compression refrigeration Cycle
Sol. ½ mark for
i) Compressor
each
ii) Condenser component

iii) Capillary (Expansion device )

iv) Evaporator

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WINTER – 2022 EXAMINATION

Model Answer

Subject Name: Power Engineering & Refrigeration Subject Code: 22562

Q. Su Answer XXXXX
Marking
No b Scheme
. Q.
N.

1. c) Define BSFC and state its unit.

Sol. Brake specific fuel consumption is the ratio of a mass flow rate of the fuel supplied to the engine to 2 marks
the brake power obtained at a crankshaft and it indicates how efficiently the fuel is used to produce
brake power.

BSFC = Mass flow rate of fuel (m)/ BP

d) Define the term FAD
Sol. Actual volume of the air delivered by the compressor when reduced to normal temperature
and pressure is known as Free air delivered (FAD) OR Free air delivery (FAD) is the enlarged volume 2 marks
of air that the compressor releases into the network within a given measure of time

e) State any two application of gas turbine .

Sol. 1. It is used for electric power generation.

2 Marks
2. It is used for locomotive propulsion. for any 2
3. It is used for ship propulsion.
application

4. Gas turbine is used in aircrafts.

5. It is used for supercharging for heavy duty Diesel engines.

6. Used in turbo jet and turbo-propeller engine.

7. It is used for various industrial purpose such as in steel industry, oil and other chemical industry.

f) Name the main components used in constant pressure cycle gas turbine.
2 marks for
Sol. Compressor
Any 2
Combustion Chember

Turbine

g) State any 2 advantages of “VVT-I”.

Reduce pumping losses.

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Smoother idle and low rpm running of engine. 2 Marks

Better torque and Increase fuel economy Any 2

Advantage
Reduce the emission of Nitric oxide (NOx) s
Controlling the cylinder temperature by valve overlap.

Better breathing of engine and Assist the scavenging process.

Increase engine life.

2. Attempt any THREE of the following: 12

a) Represent otto cycle on P-V & T-S diagram

Sol. 1.5 Marks

for PV
diagram

1.5 Marks
for TS
Diagram

1 Mark for
labeling

b) State effect of compression ratio (Rc) on Air standard efficiency of i) Otto cycle ii) Diesel Cycle

Sol. According to thermodynamics, otto cycle & Diesel has its own P-V diagram and based on that
diagram we can derive the efficiency equation. Now compression ratio is common term in all these
cycle. Compression ratio is defined as the ratio of the total volume of the cylinder to the clearance
volume of the engine. It is a fundamental specification for many common combustion engines.

Otto cycle
For Otto cycle the equation of efficiency is given by, 2 Marks
for
equations

Diesel cycle
For Diesel cycle the equation of efficiency is given by,
2 marks for
conclusion

Where r is compression ratio

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So you can see that in in above cases the efficiency equation contains, compression ratio term, so
compression ratio is an important term in all three cases.

Higher the compression ratio, higher the efficiency.

Explain working of single stage single stage single acting compressor with neat sketch
2. c)
Working :
sol.
In a single-stage reciprocating compressor, all the compression process takes place in only 2 marks for
one cylinder. Two valves connect with the cylinder, one is an inlet or suction valve, and the explanatio
other is an outlet or delivery valve. The opening and closing of a spring or plate valve vary on n
the pressure difference. When mechanical valves use for suction and discharge, their
function controls through cams.

2 marks for
Diagram

When the piston reaches at BDC, the crankcase movement helps the piston to move upward
and compresses the air. During this compression process, there is a point where the
cylinder’s internal pressure becomes higher than the external air pressure, and at this stage,
the inlet valve closes.

An outlet connects with a storage tank. As the compressed air pressure becomes higher than
the storage tank pressure, the outlet valve opens, and compressed air is released. Therefore,
this piston stroke is known as s “Delivery Stroke”. This is a compression stroke of the single-
stage air compressor. At the end of this stroke, the outlet valve opens, and the compressed
air transfers to the the receiver.

The piston moves at a very high speed inside the cylinder and continuously exerts a force on
the cylinder. Due to this reason, the compressor life reduces. To avoid this, a slight
curvature provides at the top of the cylinder.

d)
2.
Represent joules cycle on p-v & T-s Diagram

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2 marks for
P-V
diagram &
2 Marks
for T-S
Diagram

3 Attempt Any THREE of the following. 12

State advantages of CRDI system used in CI engine.
A
Advantages Of CRDI 1 Mark for
each point
• Uniform circulation of fuel to each cylinder

• Only one pump is sufficient for circulation of fuel

• Variation of pump pressure affects all cylinder uniformly

• The arrangement of system is simple and requires less maintenance

Explain the terms:

b 2 Marks
1) Compression Ratio: Compression ratio is ratio of total cylinder volume to clearance
volume.

2) B.S.F.C: It is defined as the ratio of the mass of fuel consumed per hour for unit power 2 Marks
output (Brake power). It is designated by BSFC

It is parameter which decides the economics of power production from engine.

C
Explain with neat sketch the working of Domestic Refrigerator.

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2 marks for
Sketch

Working

 The low pressure and low temperature refrigerant vapour is sucked through the
suction line to the compressor.

 The accumulator provided between the suction line and the evaporator collects
liquid refrigerant out of the evaporator. 2 Marks
for
 The compressor then compresses the refrigerant vapour to a high pressure and high
working
temperature.

 The refrigerant flows through the discharge line into condenser. In the condenser the
vapour refrigerant at high pressure and at high temperature is condensed to the
liquid refrigerant at high pressure and low temperature.

 The high pressure liquid refrigerant then flows through the filter and then enters the
capillary tube (expansion device).

 The warm refrigerant passing through the capillary tube give some of its heat to cold
suction line vapour as capillary coil is coiled around suction line.

 The capillary tube expands the liquid refrigerant at high pressure to the liquid
refrigerant at low pressure & liquid refrigerant is passed into the evaporator.

 In the evaporator the liquid refrigerant gets evaporated by absorbing heat from the
container/ articles placed in the evaporative chamber and is sucked back into the
compressor and the cycle repeated.

D
Differentiate between theoretical Otto cycle and actual Otto cycle on PV Diagram.

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3 Marks
for PV
chart(actua
l and
theoretical
)

PV chart for Theoretical and Actual Otto cycle

Comparison between theoretical and actual Otto Cycle:

Above fig. shows both theoretical and actual PV chart for Otto Cycle

 In Theoretical Otto cycle it is observed that both suction and exhaust stroke
take place at same pressure and opening and closing of valves is either at 1 mark for
TDC or BDC explanatio
 In actual PV chart of Otto cycle suction take place at below atmospheric n
pressure. inlet valve open before TDC.
 In actual PV chart of Otto cycle inlet valve closes after BDC (at point 1)
 Ignition will start before end of compression stroke.
 Exhaust valve will open before BDC (i.e. before point 4)
Exhaust will take place above atmospheric pressure and exhaust will close after TDC.

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4 Attempt any THREE of The Following 12

2 Marks

2 Marks

B Draw the neat labeled valve timing diagram for four stroke petrol engine .

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04 marks

4
c Explain Following terms in refrigeration:

i) One tonne of refrigeration:

A tonne of refrigeration is defined as the amount of refrigeration effect produced by the

uniform melting of one tonne (1000 kg) of ice from and at 0°C in 24 hours.

Since the latent heat of ice is 335 kJ/kg

1TR = 1000 x 335 kJ in 24 hours

02
In actual practice, 1TR = 210 kJ/min or 3.5 kW (i.e. 3.5 kJ/s).

Or

A tonne of refrigeration is defined as the amount of heat required to be removed to

convert 1 tonne of water at 00C to 1 tonne of ice at 00C,within the period od 24 hours.

ii) COP:

The coefficient of performance (briefly written as C.O.P.) is the ratio of heat extracted in
the refrigerator to the work done on the refrigerant. It is also known as theoretical
coefficient of performance.

02

Q = Amount of heat extracted in the refrigerator (or the amount of refrigeration

produced, or the capacity of a refrigerator)

W = Amount of work done.

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4 D Explain Following Terms

i) Isothermal efficiency:

It is defined as, "ratio of isothermal power to the indicated power". It is also called as
compressor efficiency.

02

ii) Volumetric Efficiency:

It is the ratio of free air delivered to the displacement of the compressor. It is also the
ratio of effective swept volume to the swept volume.

02

E Explain Working of closed cycle gas turbine.

4

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2 Marks

A closed cycle gas turbine, consists of a compressor, heating chamber, gas

turbine, which drives the generator and compressor and a cooling chambers.
In this turbine, the air is compressed isentropically generally in rotary
compressor and then passed in to the heating chamber. The compressed air
is heated with the help of some external source, and made to flow over the 2 Marks
turbine, blades (Generally reaction type.) The gas while flowing over the for
explnation
blades gets expanded. From the turbine the gas is passed to the cooling
chamber where it is cooled at constant pressure with the help of circulating
water to its original temp., Now the air is made to flow into compressor
again. It is thus obvious that in a closed cycle gas turbine, the air is
continuously circulated within the turbine. A closed cycle gas turbine works
on Joule’s or Bray tons cycle.
The process 1-2 shows heating of the air in heating chamber at constant
pressure. The process 2-3 shows isentropic expansion of air in the turbine
similarly the process 3-4 shows cooling of the air at constant pressure in
cooling chamber the process 4-1 shows isentropic compression of the air in
the compressor.
Work done by the turbine per kg of air
WT = CP (T2 – T3)
And
Work required by the compressor per kg of air

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WC = CP (T2 – T3)
Now, the net work available
W = WT – WC

5 12
Attempt any TWO of the following:

03

03

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5 B

02

02

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02

5
C

Chart-02

02

01

01

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6 Attempt any TWO of the following: 12

03

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03

6
B

Chart-02

02

02

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6 c

01

01

01

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0.5

0.5

0.5

0.5

01

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