SARDAR RAJA COLLEGE OF ENGINEERING, ALANGULAM (Affiliated to Anna University of Technology Tirunelveli, Regulations 2008) DEPARTMENT OF MECHANICAL ENGINEERING Subject code : ME 51 Subject Name : THERMAL ENGINEERING Question Bank UNIT I GAS POWER CYCLES Otto, Diesel, Dual, Brayton cycles, Calculation of mean effective pressure, and air standard efficiency -Actual and theoretical PV diagram of four stroke and two stroke engines. Part-A 1. What is thermodynamic cycle? 2. List out the assumptions made for the analysis of thermodynamic air cycles. 3. Sketch the Otto cycle on P-V and T-S planes and name all the processes. 4. Define air standard cycle efficiency of an Otto Cycle. 5. How does the change in compression ratio affect the air standard efficiency of an ideal Otto cycle? 6. Define MEP as applied to gas power cycles. What is its significance? 7. Write the expression for MEP for an Otto cycle in terms of compression ratio and other parameters. 8. In an Otto cycle, pressure ratio during compression is 11. Calculate the air standard cycle efficiency.
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SARDAR RAJA COLLEGE OF ENGINEERING, ALANGULAM
(Affiliated to Anna University of Technology Tirunelveli, Regulations 2008)
DEPARTMENT OF MECHANICAL ENGINEERING
Subject code : ME 51
Subject Name: THERMAL ENGINEERING
Question Bank
UNIT I GAS POWER CYCLES
Otto, Diesel, Dual, Brayton cycles, Calculation of mean effective pressure, and air
standard efficiency -Actual and theoretical PV diagram of four stroke and two
stroke engines.
Part-A
1. What is thermodynamic cycle?
2. List out the assumptions made for the analysis of thermodynamic air cycles.
3. Sketch the Otto cycle on P-V and T-S planes and name all the processes.
4. Define air standard cycle efficiency of an Otto Cycle.
5. How does the change in compression ratio affect the air standard efficiency of an
ideal Otto cycle?
6. Define MEP as applied to gas power cycles. What is its significance?
7. Write the expression for MEP for an Otto cycle in terms of compression ratio and
other parameters.
8. In an Otto cycle, pressure ratio during compression is 11. Calculate the air standard
cycle efficiency.
9. A Carnot cycle works between the temperatures 300K and 700K. Find the maximum
work possible per kg of air.
10. Sketch the Diesel cycle on P-V and T-S planes and mention the four thermodynamic
processes involved.
11. A Diesel engine has a compression ratio of 14 and cut-off takes place at 6% of the
stroke. Find the air standard efficiency.
12. Draw the actual p-v diagram for four stroke SI Engine.
13. Define air standard cycle efficiency of a diesel Cycle.
14. Name the factors that affect the air standard efficiency of diesel cycle.
15. Define the terms compression ratio and cutoff ratio.
2 Thermal Engineering
16. What is the effect of cut-off ratio on the efficiency of diesel cycle when the
compression ratio is kept constant?
17. Write any four differences between Otto cycle and Diesel cycle.
18. When the efficiency of diesel cycle approaches the Otto cycle efficiency?
19. Sketch the Dual cycle on P-V and T-S planes and mention the various processes.
20. Sketch the PV & TS diagram for Otto cycle and Diesel cycle and Dual cycle for the
same compression ratio and heat rejection, compare the efficiency.
21. For the same compression ratio and heat supplied, state the order of decreasing air
standard efficiency of Otto, Diesel and Dual cycles.
22. When will be the gas turbine cycle efficiency reaches maximum?
23. Sketch the Brayton cycle (Limited pressure cycle) on P-V and T-S planes and
mention the various processes.
24. Explain the effect of pressure ratio on the net output and efficiency of Brayton cycle.
25. Sketch the schematic arrangement of open cycle gas turbine plant and name the
components.
26. It is always useful to have a regenerator in gas turbine power cycle. Why?
27. What are the affects of reheat cycle?
Part-BOtto Cycle:
1. Derive an expression for air standard efficiency of an Otto cycle. Obtain an
expression for mean effective pressure of an Otto cycle.
2. In an engine working on constant volume cycle, the pressure, temperature and
volume at the beginning of the cycle are 1.2 bar, 35oC and 0.5 m3 respectively. At
the end of compression stroke, the pressure is 12 bar. 315 kJ of heat is added per
kg of gas during constant volume heating process. Calculate the pressure,
temperature and volume at all points. Also find the air standard efficiency of the
cycle.
3. A six cylinder petrol engine has a compression ratio of 5:1. The clearance volume
of each cylinder is 110CC. It operates on the four stroke constant volume cycle
and the indicated efficiency ratio referred to air standard efficiency is 0.56. At the
speed of 2400 rpm, it consumes 10kg of fuel per hour. The calorific value of fuel
is 44000KJ/kg. Determine the average indicated mean effective pressure.
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Prof. V. Alfred Franklin
Department of Mechanical Engineering
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4. An engine working on Otto cycle has a volume of 0.45m3, pressure 1 bar and
temperature 30oC at the beginning of compression stroke. At the end of
compression stroke, the pressure is 11bar and 210KJ of heat is added at constant
volume. Determine (i) Pressure, temperatures and volumes at salient points in the
cycle. (ii) Efficiency.
5. The compression ratio in an air-standard Otto cycle is 8. At the beginning of the
compression stroke the pressure is 0.1Mpa and the temperature is 15°C. The heat
transfer to the air per cycle is 1800 kJ/kg of air. Take Cp and Cv for air as 1.005
and 0.7 18 kJ/kg K respectively. Determine the following
(i) The pressure and temperature at the end of each process of the cycle.
(ii) The thermal efficiency.
(iii) The mean effective pressure.
6. An engine 20 cm bore and 30 cm stroke works on Otto cycle. The clearance
volume is 1600 cu cm. The initial pressure and temperature are 1bar and 60°C. If
the maximum pressure is limited to 24 bar, find the following:
(i) The air standard efficiency (ii) The mean effective pressure of the cycle.
7. An engine working on Otto cycle has a volume of 0.45 m3, pressure of
0.45 m3, pressure 1 bar and temperature 30oC at the beginning of
compression stroke. At the end of compression stroke, the pressure is 11
bars. 2 10 kJ of heat added is at constant volume. Determine
(i) Pressures, temperatures and volumes at salient point in the cycle,
(ii) Percentage of clearance
(iii) Efficiency
(iv) Mean effective pressure
(v) Ideal power developed by the engine if the number of working cycle per
minute is 210.
8. In an air standard Otto cycle the compression ratio is 6.5, and at the beginning
of isentropic compression, the temperature is 15oC and the pressure is 1 bar. Heat
is added during constant volume process so that the maximum temperature in the
cycle is 1480CC. Calculate
(i) The heat supplied per kg of air,
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4 Thermal Engineering
(ii) The cycle efficiency and
(iii) The mean effective pressure
Diesel Cycle:
1. Derive an expression for mean effective pressure of a Diesel cycle in terms of
pressure ratio, cutoff ratio and compression ratio.
2. An air standard Diesel cycle has a compression ratio of 12 and cutoff takes place
at 6% of the stroke. Calculate the air standard efficiency of the cycle.
3. 1kg of air is taken through a diesel cycle. Initially the air is at 25oC and 1 bar. The
compression ratio is 14 and the heat added is 1850KJ. Calculate the ideal cycle
efficiency and the mean effective pressure.
4. Draw the theoretical and actual P.V. diagrams for 4-stroke diesel engine and
explain why in practice the actual condition differs from the ideal condition.
5. In an air standard Diesel cycle, the compression ratio is 18, and at the beginning
of isentropic compression, the temperature is 27CC and the pressure is 0.1 MPa.
1800 kJ of heat is added at constant pressure. Calculate i) the cut-off ratio, ii) the
heat supplied per kg of air iii) the cycle efficiency and iv) mean effective pressure
Dual Cycle:
1. With the help of p-v and T-s diagrams, show that for the same maximum
pressure
and temperature of the cycle and the same heat rejection
ηDiesel > ηDuaI < ηOtto
2. In a dual cycle the air is compressed isentropically to 1/14th of its initial volume.
At the end of compression heat is added at constant volume till its pressure
increases to twice the pressure at the end of compression. Then heat is added at
constant pressure till its volume increases to twice the volume after compression.
Find the efficiency of the cycle.
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Prof. V. Alfred Franklin
Department of Mechanical Engineering
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3. In engine working on Dual cycle, the temperature and pressure at the beginning
of cycle are 90oC and one bar. The compression ratio is 9. The maximum
pressure is limited to 68bar and total heat supplied per kg of air is 1750kJ.
Determine air standard efficiency and mean effective pressure.
4. A dual combustion air standard cycle has a compression ratio of 10. The constant
pressure part of combustion takes place at 40 bar. The highest and the lowest
temperatures of the cycle are 1727° C and 27° C respectively. The pressure at the
beginning of compression is 1 bar. Calculate (i) the pressures and temperatures at
key points of the cycle,(ii)the heat supplied at constant volume, (iii) the heat
supplied at constant pressure, (iv) the heat rejected, (v) the work output, (vi) the
efficiency and (vii) MEP.
6. An air standard dual cycle has a compression ratio of 16 and compression
begins at1.013 bar, 50°C. The maximum pressure is 70 bar. The heat
transferred to air at constant pressure is equal to that at constant volume.
Estimate the temperatures at the cardinal points of the cycle and the cycle
efficiency.
7. An air-standard Dual cycle has a compression ratio of 10. The pressure
and temperature at the beginning of compression are I bar and 27°C. The
maximum pressure reached is 42 bar and the maximum temperature us
1500oC Determine
(i) The temperature at the end of constant volume heat addition
(ii) Cut-off ratio
(iii) Work done per kg of air and
(iv) Net work output per kg
(v) Cycle efficiency
Brayton Cycle:
1. Derive an expression for air standard efficiency of a Brayton cycle in terms of
pressure ratio and compression ratio. Also prove that the pressure ratio for
maximum work is a function of limiting temperature ratio.
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6 Thermal Engineering
2. The extreme of pressure and temperature in an open circuit constant pressure
gas turbine plant are 1 bar, 5.25bar and 25oC and 560oC respectively. The
isentropic efficiency of the turbine is 88% and that of the compressor is 84%.
Determine the efficiency of the plant.
3. A gas turbine works on an air standard Brayton cycle. The initial condition
of the air is 25°C and 1 bar. The maximum pressure and temperature are
limited to 3 bar and 650°C. Determine the following:
(i) Cycle efficiency
(ii) Heat supplied and heat rejected/kg of air
(iii) Work output/kg of air
(iv) Exhaust temperature
4. Air enters the compressor of a gas turbine at 100 kPa and 25° C. For a pressure
ratio of 5 and a maximum temperature of 850°C determine the thermal
efficiency using the Brayton cycle.
5. An air standard Limited pressure cycle has a compression ratio of 15 and
compression begins at 0.1MPa, 40°C. The maximum pressure is limited
to 6MPa and the heat added is 1.675 MJ/Kg. Compute
(i) The heat supplied at constant volume per kg of air, and the heat supplied
at constant pressure per kg of air.
(ii) The work done per kg of air, the cycle efficiency, and the temperature at
the end of the constant volume heating process.
iii) The cut-off ratio, and iv) The m.e.p. of the cycle.
UNIT II INTERNAL COMBUSTION ENGINES
Classification - Components and their function - Valve timing diagram and port
timing diagram - Comparison of two stroke and four stroke engines – Carburettor
system, Diesel pump and injector system. Performance calculation – Comparison of
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Prof. V. Alfred Franklin
Department of Mechanical Engineering
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petrol and diesel engine - Lubrication system and Cooling system – Battery and
Magneto Ignition System – Formation of exhaust emission in SI and CI engines.
Part-A
1. Write any two major differences between 'SI engine' and 'CI engine'.
2. Compare two stroke and four stroke engines.
3. Why diesel engines are more efficient than petrol engines?
4. Which is better efficient two stroke or four stroke engines? Why?
5. What is the function of camshaft and crankshaft?
6. What is the function of pushrod and rocker arm?
7. What are the functions of piston rings?
8. Name the basic thermodynamic cycles of two types of internal combustion
reciprocating engines.
9. What is meant by highest useful compression ratio?
10. Why compression ratio of a petrol engine is low while diesel engines have high
compression ratio?
11. Compare the thermal efficiency of petrol engines with diesel engines. Give
reasons.
12. Why the actual cycle efficiency is much lower than the air-standard cycle
efficiency? List and explain the major losses in an actual engine.
13. State the air-fuel ratio requirements of SI engine under various operating
conditions.
14. Differentiate between ideal and actual valve timing diagram of a petrol engine.
15. Draw port-timing diagram of petrol engine.
16. What is scavenging in IC engines?
17. Define Cetane number of a fuel.
18. What is the function of a carburettor? What is carburetion?
19. Why a choke is used in carburettor and what is meant by automatic chocking?
20. What are the limitations of simple carburettor?
21. During peak power operation, why petrol engine requires rich mixture?
22. Mention the different types of fuel injection system in CI Engine.
23. What are the basic requirements of a fuel injection system of a diesel engine?
24. What do you understand by air injection and solid injection?
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8 Thermal Engineering
25. Define delay period with respect to a CI Engine.
26. Differentiate brake power and indicated power.
27. What are the various methods to determine the FHP of a engine?
28. Differentiate between SFC and TFC in engine performance.
29. What is the necessity of cooling in IC engines?
30. What is the purpose of thermostat in an engine cooling system?
31. What is the need of lubrication system for IC engines?32. What is splash lubrication?
33. What do you mean by mist lubrication?
34. List the advantages and disadvantages of battery ignition system. Also draw the
V-N curve.
35. List the advantages of electronic ignition system over the conventional systems.
36. List out the effects of detonation.
Part-B
1. (a) Explain any four types of classification of internal combustion engines.
(b) Draw the valve timing diagram for a 4 stroke SI Engine.
2. Describe with a suitable sketch the two-stroke cycle spark ignition (SI) engine.How
its indicator diagram differs from that of four-stroke cycle engine?
3. (a) Explain any four types of classification of Internal Combustion engines.
(b) With a neat sketch explain any one type of ignition system.
4. Explain the working of 4-stroke cycle Diesel engine. Draw theoretical and actual
valve-timing diagram for the engine. Explain the reasons for the difference.
5. (a) Explain why cooling is necessary in an I.C. engine.
(b) With neat sketches describe the working of Water Cooling System used for multi
cylinder engine.
Sardar Raja College 0f Engineering, Alangulam
Prof. V. Alfred Franklin
Department of Mechanical Engineering
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6. Explain why cooling is necessary in I.C. engine. With neat sketches describe the
working of water cooling system used for multi-cylinder engine. Why should a pump and
thermostat be provided in the cooling system of an engine?
7. Explain with neat sketches the method of lubrication of the following parts of the I.C.
Engines. (i) Piston and cylinder
(ii) Crank-pin and Gudgeon pin
(iii) Cam-shaft.
8. (i) Explain with neat sketch Air Cooling of Engines.
(ii) Explain any one lubrication system adopted in multi cylinder SI engines.
9. Explain the principle of Magneto ignition system. Enumerate its advantages and
disadvantages?
10.(a) What are the various factors influencing the flame speed in SI Engines? (8)
(b) Explain the combustion phenomenon in SI Engines. (8)
11. (a) What is the purpose of cooling an I.C. Engine?
(b) What are the ill effects of improper cooling?
(c) With neat sketches, describe how a fuel injection pump supplies fuel to a
diesel engine for different load conditions.
(d) Explain the normal combustion and knocking in a diesel engine with
pressure-crank angle diagram
12. (i) Explain the function of a fuel injection pump with a simple sketch. (8)
(ii) What are the advantages and disadvantages of Magneto ignition system over Batter
ignition system? (8)
13. (a)Draw the port timing diagram with fuel injection of a two-stroke diesel engine and
explain the salient points.
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10 Thermal Engineering
(b) Explain the effects of time loss factor and heat loss factor with suitable graphs on
the performance of actual I.C. Engines
14. (i) Explain the phenomenon of knock in SI engine. What are the different factors
which influences the knocking? Describe the methods used to suppress it. [9]
(ii) With a neat sketch explain magneto and coil ignition system. [7]
15.(a) Compare the petrol and diesel engines with reference to the following:
(1) Power to weight ratio
(2) Acceleration response
(3) Economy in road transport
(4) Maintenance and repair.
(b) Enumerate the desirable properties of a good fuel for a petrol engine. (4)
(c) Explain the significance of flame speed and its influence on combustion in
S.I.engine.
16.(a) Explain the phenomenon of knock in CI engine. Describe the methods used to
suppress it. Compare the knocking in Diesel engine with that of petrol engine.
(b) The petrol used in an engine is approximated to both methane and ethane. Calculate
the theoretical A/F Ratio. If 30% of excess air is supplied, find the actual A/F ratio.
17. (a) A six cylinder, 4 stroke SI engine having a piston displacement of 700 cm3 per
cylinder developed 78 kW at 3200rpm and consumed 27 kg of petrol per hour. The
calorific value of petrol is 44 MJ/kg. Estimate
i. The volumetric efficiency of the engine if the air fuel ratio is 12
and intake air is at 0.9 bar, 32oC.
ii. The brake thermal efficiency, and
iii. The braking torque.
(b) Describe a simple carburetor with a neat sketch and also state its limitations.
Sardar Raja College 0f Engineering, Alangulam
Prof. V. Alfred Franklin
Department of Mechanical Engineering
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18. Following data relates to 4 cylinders, 2 stroke petrol engine. Air/Fuel ratio by weight
16:1. Calorific value of the fuel = 45200 kJ/kg, mechanical efficiency = 82%. Air