Code :9A03402 1II B.Tech II Semester(R09) Regular Examinations, April/May 2011

THERMAL ENGINEERING-I(Mechanical Engineering)

Time: 3 hours Max Marks: 70Answer any FIVE questions

All questions carry equal marks⋆ ⋆ ⋆ ⋆ ⋆

1. (a) Define volumetric efficiency and discuss the effect of various factors affecting the volumetricefficiency.

(b) How does the composition of exhaust gases vary for various fuel-air ratios in a gasolineengine?

2. (a) Draw a typical value timing diagram for a four stroke diesel engine and explain the signif-icance of value over lap.

(b) Compare between Air - standard cycles and Fuel-air cycles.

3. (a) What is meant by abnormal combustion? Explain the phenomena of knock in s1 engines.

(b) What are homogeneous and heterogeneous mixtures? In which engines these mixtures areused? Explain.

4. Explain with figure various types of combustion chambers used in c1 engines.

5. (a) Explain the method of motoring test for obtaining friction power of an engine.

(b) Find the air - fuel ratio of a four- stroke, single cylinder, air coded engine with fuelconsumption time for 10cc is 20.4s and air consumption time for 0.1m3 is 16.35. Theload is 17Kg at the speed of 3000rpm . Find also brake specific fuel. Consumption ing/KWh and brake thermal efficiency. Assume the density of air as 1.175 Kg/m3 andspecific gravity of fuel to be 0.7. The lower heating value of fuel is 43 MT/kg and thedynamometer constant is 5000.

6. Explain the effect of excessive clearance on the performance of air compressor. A single actingtwo stage reciprocating air compressor running at 280 rev/min delivers air at a pressure of18 bar, the conditions at the commencement of compression being 0.098 bar and 305K. Theintermediate pressure is 4 bar and the clearance volume for low pressure cylinder is 5% of itsswept volume. Equation of compressor has a capacity of 2.25 m3/minute measured under freeconditions of 1 bar and 290 k. Design the compressor for (a) volumetric efficiency (b) theoreticalwork spent in driving the compressor (c) dimensions of L.P. cylinder 1f bore is equal to stroke(d) isothermal efficiency, The gives compressor has a perfect intercooling.

7. (a) Write a brief note on Rotary displacement compressors and derive an expression for theefficiency of Roots blower.

(b) Explain the terms serging & choking of a compressors.

8. (a) Explain the working of an axial flow compressor.

(b) Explain the term degree of reaction and point on the difference between the blading of areaction turbine and that of axial flow compressor.

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Code :9A03402 2II B.Tech II Semester(R09) Regular Examinations, April/May 2011

THERMAL ENGINEERING-I(Mechanical Engineering)

Time: 3 hours Max Marks: 70Answer any FIVE questions

All questions carry equal marks⋆ ⋆ ⋆ ⋆ ⋆

1. (a) Briefly explain the following : (i) time loss factor (ii) heat loss factor (iii) exhaust blowdown factor.

(b) Compare the actual and fuel - air cycles of a Diesel engine.

2. (a) List various assumptions made in air - standard cycle analysis and explain how the actualcycles are different form air standard cycle.

(b) Explain how the power and efficiency of the S1 engine vary with air - fuel ratio for differentload and speed conditions.

3. (a) Explain the effect of various engine variable on S1 engine knock.

(b) Explain the various factors that influence the flame speed in S1 engines.

4. (a) Explain the phenomenon of knock in C1 engines and compare it with S1 engine knock.

(b) What are homogeneous and heterogeneous mixtures? In which engines these mixtures areused? Explain.

5. (a) With a neat sketch explain an Eddy current dynamometer.

(b) A six - cylinder, gasoline engine operators on the four - stroke cycle. The bore of eachcylinder is 80mm and the stroke 100mm. The clearance volume per cylinder is 70cc. At aspeed of 4000rpm the fuel consumption is 20 Kg/h and the torgue developed is 150 Nm.Calculatei. the brake powerii. the brake mean effective pressureiii. brake thermal efficiency is the calorific value of the fuel is 43000 KJ/Kg andiv. the relative efficiency on a brake power basis assuming the engine works on the con-

stant volume cycle. γ = 1.4 for air.

6. An air Compressor designed to deliver air at 8 bar a stroke length 80cm and the clearancevolume is 2% of the swept volume. To study the effect of clearance on free air delivery at workexpanded. The compressor was overhauled and a distance piece of 0.5cm was filled betweenthe cylinder head and the cylinder. The compressor was then commisined under the changedclearance. Calculate percentage change in the volume of free air delivered and the powernecessary to run the compressor.

7. (a) Explain the performance characteristics of Rotary compressors.

(b) Give a detailed classification of Rotary compressors.

8. A multi stage axial floe compressor absorbs H.P when delivering 20 Kg/sec of air from stagna-tion condition of I bar and 288 K. If the poly tropic efficiency of compression is 0.9 and if thestage stagnation pressure ratio is constant, calculate

(a) pressure at compressor out let

(b) the number stager and

(c) over all isentropic efficiency of compressor.

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Code :9A03402 3II B.Tech II Semester(R09) Regular Examinations, April/May 2011

THERMAL ENGINEERING-I(Mechanical Engineering)

Time: 3 hours Max Marks: 70Answer any FIVE questions

All questions carry equal marks⋆ ⋆ ⋆ ⋆ ⋆

1. (a) Discuss the effect of spark advance on the performance of an otto cycle engine. What is meantby the optimum spark advance?

(b) Briefly discuss pumping and rubbing Friction losses. Discuss briefly the loss due to gas exchangeprocess.

2. (a) With a neat sketch explain the working principal of a simple carburetor.

(b) Explain various Factors which effect the ignition timing.

3. (a) Briefly explain the stages of combustion in S1 engines elaborating the flame front propagation.

(b) What are homogeneous and heterogeneous mixtures? In which engines mixtures are used Explain.

4. (a) What is delay period and what are the factors that effect the delay period?

(b) Explain the phenomena of knock in C1 engines?

5. (a) Explain the internationally accepted methods of measuring the following invisible emission.(i) oxides of nitrogen(ii) carbon monoxide

(b) The following details were noted in a test on a four - cylinder, four - stroke engine, diameter =100mm; stroke = 120mm; speed of the engine = 1600 rpm; fuek consumption = 0.2 Kg/min;calorific value of fuel is 44000 KJ/Kg; difference in tension on either side of the brake pulley =40 Kg; brake circumference is 300cm. If the mechanical efficiency is 80% calculate

i. brake thermal efficiencyii. indicated thermal efficiencyiii. indicated mean effective pressure andiv. brake specific fuel consumption.

6. A single cylinder reciprocating air compressor running at 150rpm delivers to a receiver 5m3 of freeair per minute. Compressed to a pressure of 6 Kgf/cm2. The suction is at 1 Kgf/cm2 and 300k.Compression and expension. Curve follows the law pv1.3=c. Clearance is 5% of the active stroke.Estimate.

(a) Temperature of air as admitted to receiver.

(b) Volumetric efficiency

(c) Volumetric of air taken in per stroke

(d) Dimension of the cylinder if stroke equals 1.25 times diameter.

(e) H.p of compressor.

7. A Rotary vane compressor has a free air delivery of 0.03 m3/revolution when it compressor from 1 barto 1-5 bar. Estimate the work expended for revolution in driving the compressor when (a) ports areS0 placed that there is no internal compression (b) The ports so placed that there is 50% pressure risedue to internal adiabatic compression before have flow occurring also determine the blower efficiency.

8. An axial compressor has a degree of reaction of 0.5 at the mean radius with relative air angles of 1300

and 1000 at rotor inlet and outlet respectively. The angles are measured in the same direction fromthe blade velocity direction. The over all stagnation pressure ratio is 3.5 and the stagnation isentropicefficiency is 85% when the inlet stagnation temperature is 3300k. The blade speed is constant at 200m/s and the flow velocity is also constant in the compressor. The work done factor is 0.85. Find thestagnation polytropic efficiency and the number of stages.

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Code :9A03402 4II B.Tech II Semester(R09) Regular Examinations, April/May 2011

THERMAL ENGINEERING-I(Mechanical Engineering)

Time: 3 hours Max Marks: 70Answer any FIVE questions

All questions carry equal marks⋆ ⋆ ⋆ ⋆ ⋆

1. (a) Why the actual cycle efficiency is much lower than the air standard cycle efficiency? Listthe major losses and differences in actual engine and air standard cycles.

(b) Discuss the optimum opening position of exhaust value to reduce the exhaust blowdownloss.

2. (a) Enumerate various components of an electronic fuel in system and mention their functions.

(b) Distinguish between wet sump and dry sump lubrication systems.

3. What are the various types of combustion chambers used in S1 engines? Explain them briefly.

4. Bring out clearly the process of combustion in C1 engines and also explain the various stagesof combustion.

5. (a) State the limitations experienced in the evaluation of friction power using Willan’s linemethod.

(b) A four - stroke gas engine having a cylinder of 250mm diameter and stroke 450mm has avolumetric efficiency of 80%, ratio of air to gas is 8 to 1, calorific value of gas is 20 MJ/m3

at NTP. Find the heat supplied to the engine per working cycle. If the compression ratiois 5, What is the heating value of the mixture per working stroke per m3 of total cylindervolume?

6. Discuss concisely the reason for the use of multistage reciprocating compressors. Explain theunderlying principle by means. Of a P-V and T-S diagram,It is required to compress 1m3 of air/s from 0.98 bar and 200C to a delivery pressure of 60bar. The compression of air follows the polytropic law PV1.25= c. Estimate theoretical powerrequired when compression is carried out in (a) Single stage compressor (c) Three stage com-pressor. Also estimate the temperature of air at the end of compression in each case. Neglectclearance and assume ideal conditions regarding intercooling . Comment on the results.

7. (a) Explain the working of centrifugal compressor.

(b) Explain the terms serging & choking of a compressor.

8. An eight stage axial flow compressor provides an over all pressure ratio of 6:1 with an overallisentropic efficiency 90% when the temperature of air at inlet is 200. The work is divided equallybetween stages. A 50% reaction design is used with a mean blade speed 188m/s and a constantaxial velocity 100m/s through the compressor ultimate the power required and blade angles.Assume air to be a perfect gas for which Cp=0024, γ = 104.

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Code: 9A03402

II B. Tech II Semester (R09) Supplementary Examinations, November/ December 2011 THERMAL ENGINEERING - I

(Mechanical Engineering) Time: 3 hours Max Marks: 70

Answer any FIVE questions All questions carry equal marks

***** 1 (a) What do you understand from degree of reaction? (b) An axial flow compressor with compression ratio of 1.4 draws in air at 22o C. The compression

process is approximated as an isentropic process. The stagnation conditions at this stage is 300 K. the blade velocity being 200 m/s. Draw the velocity triangles for an air angle of 20o

and determine vane angles. Also calculate the degree of reaction.

2 (a) What do you understand from gas exchange process in an engine and how it affects the

performance of I.C engine? (b) What do you understand from air standard cycle? What are the assumptions made for accurate

analysis of internal combustion engine process? 3 (a) A gas engine having a cylinder 250mm bore and 450mm stroke has a volumetric efficiency of

80%. Air-gas ratio equals 9:1, calorific value of fuel 21000 kJ/m3 at NTP. Calculate the heat supplied to the engine per working cycle. If the compression ratio is 5:1, what is the heat value of the mixture per working stroke per m3

of total cylinder volume?

(b) Explain the performance test of an IC engine. Why is it carried out? 4 (a) Briefly explain any two methods of fuel injection systems generally employed in C.I engines. (b) Compare Otto and diesel engines. 5 (a) What are the primary considerations in designing a combustion chamber for C.I engine? (b) State the factors on which delay period in C.I engine depends. 6 (a) Define volumetric efficiency and explain the effect of clearance volume and pressure ratio on

volumetric efficiency. (b) Estimate the minimum work required to compress 2 kg of air from 1 bar 330 K to 18 bar in two

stages if the law of compression is pV1.25

= constant and inter cooling is perfect.

7 (a) What are different types of rotary compressors and explain briefly the working of any two rotary

compressors. (b) With the help of h-s diagram, compare actual and isentropic compressions. 8 (a) What are knock limited parameters in case of combustion engines? (b) What are homogeneous and heterogeneous mixtures? Explain in which engines these mixtures

are used.

*****

R09

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Code: 9A03402

II B. Tech II Semester (R09) Regular & Supplementary Examinations, April/May 2012 THERMAL ENGINEERING - I

(Mechanical Engineering) Time: 3 hours Max Marks: 70

Answer any FIVE questions All questions carry equal marks

*****

1 (a) Why actual cycle is different from air standard cycle for I.C engine? Give few reasons. (b) Explain in detail the effect of time loss in the mixing of fuel and air and also in combustion

in case of I.C engine. 2 (a) Explain the working of a two-stroke engine with neat sketch. Also draw the P-V diagram. (b) What is ignition system in I.C engines and explain battery ignition system used in petrol

engines? 3 (a) What is knocking and what are the factors affecting knock? (b) Differentiate pre-ignition, auto ignition and detonation. 4 What do you understand from fuel requirements and fuel rating of C.I engine? Explain in

detail. 5 (a) Define indicated power and how it can be determined experimentally for multi cylinder

engine. (b) A four cylinder, four stroke diesel engines has brake mean effective pressure of 5.5 bar

at full load speed of 600 rpm and specific fuel consumption of 0.25 kg/kWh. The cylinder has bore of 25 cm and stroke length of 35 cm. The air fuel ratio is measured as 26 from the exhaust gas analysis. The ambient conditions are 1 bar, 27ºC. Assuming the calorific value of fuel as 44 MJ/kg. Determine the brake thermal efficiency and the volumetric efficiency. Also find out brake power.

6 (a) Estimate the minimum work required to compress 1 kg of air from 1 bar 300 K to 16 bar

in two stages if the law of compression is pV1.3 = constant and inter cooling is perfect. (b) Explain the working of blower and compressor. 7 (a) How does the pressure rise in a centrifugal compressor? Where the compressed air is

used? (b) A centrifugal compressor delivers free air of 20 kg/min. Air is sucked at static states of 1

bar, 27o C with inlet velocity of 100 m/s. The total head pressure ratio is 6 and isentropic efficiency of compressor is 82%. The mechanical efficiency of motor attached is 90%. Determine total temperature of air at exit o compressor and power required to drive compressor.

8 (a) Explain the working of an axial flow compressor with the help of neat sketch. (b) Derive expression for polytropic efficiency in terms of entry and delivery pressures,

temperature and ratio of specific heats. *****

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Code: 9A03402

II B. Tech II Semester (R09) Regular & Supplementary Examinations, April/May 2012 THERMAL ENGINEERING - I

(Mechanical Engineering) Time: 3 hours Max Marks: 70

Answer any FIVE questions All questions carry equal marks

*****

1 (a) List out few actual and air standard cycles. (b) List the major losses in actual cycles and air standard cycles. 2 (a) What is I.C engine and briefly explain how they are classified? (b) Explain with neat sketch the construction and working of fuel pump. 3 (a) Briefly explain the importance of flame speed on combustion. (b) What are the requirements of combustion chamber? 4 (a) What is delay period in C.I engine? What is the difference between physical delay and

chemical delay? (b) Enlist the various methods of controlling diesel knock. 5 (a) A diesel engine has a bore of 0.1 m, stroke of 0.11 m and a compression ratio of 19

running at 2000 rpm. Each cycle takes two revolutions and had a mean effective pressure of 1400 kPa. With total of six cylinders, find the indicated power.

(b) What are the methods to measure the fuel consumption of I.C engine? Explain any one method with the help of diagram.

6 (a) Define volumetric efficiency and explain the effect of clearance volume and pressure

ratio on volumetric efficiency. (b) Estimate the minimum work required to compress 2 kg of air from 1 bar 330 K to 18 bar

in two stages if the law of compression is pV1.25 = constant and inter cooling is perfect. 7 (a) A gas turbine utilizes a two-stage centrifugal compressor. The pressure ratios for the first

and second stages are 2.5:1 and 2.1:1 respectively. The flow of air is 1.5 kg/s, and is being at 1.013 bar and 283 K. If the temperature drop in the intercooler is 50oC and isentropic efficiency is 0.85 for each stage. Calculate: (i) the actual temperature at end of each stage, (ii) the total compressor power. Take γ =1.4 and Cp = 1.005 kJ/kg k.

(b) What are the different shapes of impeller blades used in the centrifugal compressor? 8 (a) Compare the axial flow compressor with centrifugal compressors (b) An axial flow compressor stage has a mean diameter of 600 mm and runs at 12000 rpm.

mass flow rate through the compressor is 60 kg/s. Determine the power required to drive the compressor and degree of reaction if the air angle is 15o. The vane angle at inlet and exit are equal to 45o and 25o respectively.

*****

2

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Code: 9A03402

II B. Tech II Semester (R09) Regular & Supplementary Examinations, April/May 2012 THERMAL ENGINEERING - I

(Mechanical Engineering) Time: 3 hours Max Marks: 70

Answer any FIVE questions All questions carry equal marks

*****

1 (a) What are the components of four-stroke IC engine and explain its functions? (b) What is the necessity of carburetor in S.I engine and explain its working principle? 2 (a) What do you understand from gas exchange process in an engine and how it affects the

performance of I.C engine? (b) What do you understand from air standard cycle? What are the assumptions made for

accurate analysis of internal combustion engine process? 3 (a) What do you understand from normal combustion and what are the factors affecting

normal combustion in S.I engines? (b) Explain the difference between pre-ignition, auto ignition and detonation. 4 (a) What do you mean by Octane number and Cetane number of fuels? (b) What is supercharging of IC engine? Write few applications. 5 (a) A petrol engine develops 20 kW of brake power. If the brake thermal efficiency and

mechanical efficiencies of the engine are 25% and 80% respectively, calculate the indicated thermal efficiency.

(b) Define indicated mean effective pressure related to I.C engine and how it can be measured?

6 (a) Derive the expression for the reversible work of compression with and without clearance,

when the compression process is polytropic. (b) Differentiate positive displacement and non-positive displacement compressor. 7 (a) What is vane type compressor? Briefly explain its operating principle. (b) Estimate the efficiency of the vane compressor when it handles 0.15 m3 of air per second

from 1 bar to 3 bar. The pressure rise due to compression in the compressor is limited to 1.9 bar. Also calculate the power required to run the compressor if mechanical efficiency is 85%.

8 (a) Explain the mechanical details and working principle of an axial flow compressor. (b) An axial flow compressor draws air at 1 bar and 20o C. Assuming 50% degree of

reaction, find the velocity of flow if the blade velocity is 100 m/s. Take air angle, vane angle at inlet are 10o and 40o respectively. Estimate the work done per kg of air and power developed if the flow area is 0.2 m2.

*****

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Code: 9A03402

II B. Tech II Semester (R09) Regular & Supplementary Examinations, April/May 2012 THERMAL ENGINEERING - I

(Mechanical Engineering) Time: 3 hours Max Marks: 70

Answer any FIVE questions All questions carry equal marks

***** 1 (a) What is volumetric efficiency? Explain different factors which affect the volumetric efficiency

of any engine. (b) Explain the optimum opening position of exhaust valve to reduce the exhaust blow down

loss in gasoline engine. 2 (a) Draw the valve-timing diagram of four-stroke engine and mark the various processes on it (b) What is fuel supply system and explain methods of fuel system generally employed in

spark ignition engines. 3 (a) Write short notes on pre-ignition and knocking. (b) What are homogeneous and heterogeneous mixtures? Explain in which engines these

mixtures are used. 4 What are the different methods used in C.I engines to create turbulence in the mixture?

Explain its effect on power output and thermal efficiency of the engine. 5 (a) Briefly explain the measurement of brake power of IC engine by using prony brake

dynamometer. (b) A two stroke two cylinder engine runs with speed of 2000 rpm and fuel consumption of 3

liters/hr. The fuel has specific gravity of 0.8 and air-fuel ratio is 18. The piston speed is 500 m/min and indicated mean effective pressure is 5 bar. The ambient conditions are 1.013 bar, 15ºC. The volumetric efficiency is 0.7 and mechanical efficiency is 0.8. Determine brake power output considering R for gas = 0.287 kJ/kg K.

6 (a) What is the function of a compressor and what are the different types of compressors? (b) Derive the expression for work of compression without clearance, when the compression

process is reversible adiabatic and reversible isothermal. 7 (a) Derive expression for roots blower efficiency. (b) A centrifugal compressor running at 3000 rpm has internal and external diameters of

impeller as 425 mm and 625 mm respectively. The vane angles at inlet and outlet are 25o and 45o respectively. The air enters the impeller radially. Determine work done by the compressor per kg of air and degree of reaction.

8 (a) An axial flow compressor stage has a mean diameter of 600 mm and runs at 250 rps.

Mass flow rate through the compressor is 50 kg/s. Determine the power required to drive the compressor and degree of reaction if the air angle is 12o. The vane angle at inlet and exit are equal to 35o and 27o respectively.

(b) What do you understand by 50% reaction balding? *****

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Code: 9A03402

B. Tech II Year II Semester (R09) Supplementary Examinations, November/December 2012 THERMAL ENGINEERING - I

(Mechanical Engineering) Time: 3 hours Max. Marks: 70

Answer any FIVE questions All questions carry equal marks

*****

1 (a) Explain in detail the effect of time loss in the mixing of fuel and air and also in combustion in case of I.C engine.

(b) Explain in detail the effect of heat loss from gases to cylinders in case of I.C engines. 2 (a) Explain any one method of spark ignition system that is employed in S.I engines with

neat sketch. (b) Explain different ignition systems employed in S.I engine. 3 (a) With the help of pressure-crank angle diagram, explain the normal combustion in spark

ignition engines. (b) Define homogeneous mixture. 4 Explain in detail the stages of combustion in C.I engine. 5 (a) Briefly explain the measurement of brake power of IC engine by using rope brake

dynamometer. (b) Determine the dimensions of cylinder, brake thermal efficiency and indicated mean

effective pressure for the single cylinder four stroke diesel engines producing 100 kW of brake power. Engine runs at speed of 400 rpm, brake mean effective pressure of 850 kPa, brake specific fuel consumption of 0.335 kg/kW hr. The mechanical efficiency is 0.8 and stroke to bore ratio is 1.25. The calorific value of fuel may be taken as 43.5 MJ/kg.

6 (a) Briefly explain the working of fan, blower and compressor. (b) A three stage single acting reciprocating air compressor delivers 2.5 m3 of free air per

minute from 1 bar to 72 bar. Calculate the power required to operate compressor if n = 1.3. The mean piston speed is 140 m/min. Find the piston area, neglecting the clearance volume.

7 (a) What are different types of rotary compressors and explain briefly the working of any

two rotary compressors? (b) With the help of h-s diagram, compare actual and isentropic compressions. 8 (a) Explain very briefly why work done factor needs to be considered in a multi stage axial

compressor and how it is applied. (b) An axial flow air compressor is designed to provide an overall total-to-total pressure ratio

of 8 to 1. At inlet and outlet the stagnation temperatures are 300 K and 586.4 K, respectively. Determine the overall total-to-total efficiency and the polytropic efficiency for the compressor. Assume that for air is 1.4.

*****

R09

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Code: 9A03402

B.Tech II Year II Semester (R09) Regular & Supplementary Examinations, April/May 2013 THERMAL ENGINEERING - I

(Mechanical Engineering) Time: 3 hours Max Marks: 70

Answer any FIVE questions All questions carry equal marks

*****

*****

1 (a) Explain in detail the effect of exhaust valve opening time on blow down in case of gasoline engine. (b) Discuss briefly the loss due to gas exchange process in gasoline engine 2 (a) Briefly explain any two methods of fuel injection systems generally employed in C.I engines. (b) Compare Otto and diesel engines. 3 Briefly explain the effect of different factors on knock in SI engines. 4 What are the factors affecting the delay period? Explain in detail. 5 (a) Define indicated mean effective pressure related to I.C engine and how it can be measured? (b) A two cylinder four stroke engine runs at 240 rpm developing a torque of 5 kN-m. The bore and

stroke of cylinder are 30 cm and 60 cm respectively. Engine runs with gaseous fuel having calorific value of 16.8 MJ/m3. The gas and air mixture is supplied in proportion of 1:7 by volume. The volumetric efficiency is 0.85. Determine: (i) The brake power. (ii) The mean piston speed in m/s. (iii) The brake mean effective pressure. (iv) The brake thermal efficiency.

6 (a) A single stage double acting air compressor running at 300 rpm, delivers 15 m3 of free air per

minute at 700 kPa and 2000 C. If the clearance volume is 8% of swept volume and if the index of compression and expansion are same. Find the clearance swept volume of piston and volumetric efficiency. Initial air conditions are 10 kP and 150 C.

(b) Draw the T-S diagram for the multi stage compression and show the work saving during the compression in comparison with single stage reciprocating air compression.

7 (a) With the help of neat sketch, explain the working of vane type blower. Also show the compression

process in P-V diagram. (b) A Vaned compressor handles free air of 0.6 m3/s at 1 bar and compresses to 2.3 bar. There occurs

30% reduction in volume before the back flow occurs. Determine the indicated power required and isentropic efficiency.

8 (a) Derive expression for polytropic efficiency in terms of entry and delivery pressures, temperature

and ratio of specific heats. (b) An axial flow compressor is to have constant axial velocity of 250 m/s and 50% degree of reaction.

The mean diameter of blade ring is 45 cm and speed is 18000 r.p.m. The exit angles of the blade are 250. Calculate blade angle at inlet and work done per kg of air with the help of velocity triangles.

1

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Code: 9A03402

B.Tech II Year II Semester (R09) Regular & Supplementary Examinations, April/May 2013 THERMAL ENGINEERING - I

(Mechanical Engineering) Time: 3 hours Max Marks: 70

Answer any FIVE questions All questions carry equal marks

*****

*****

1 (a) Define volumetric efficiency of engine and discuss the effect of various factors that affect the volumetric efficiency.

(b) Compare the actual and fuel-air cycles of IC engine 2 (a) Sketch the battery ignition system and explain its working. (b) Explain the various types of cooling systems employed in IC engines. 3 Explain the phenomenon of knocking in S.I engine. What are the effects of knocking? 4 Explain with neat sketch the working principle of combustion chamber used in CI engine. 5 (a) A four stroke four cylinder diesel engine running at 300 rpm produces 250 kW of brake power.

The cylinder dimensions are 30 cm bore and 25 cm stroke. Fuel consumption rate is 1 kg/min while air fuel ratio is 10. The average indicated mean effective pressure is 0.8 MPa. Determine indicated power, mechanical efficiency, brake thermal efficiency and volumetric efficiency of engine. The calorific value of fuel is 43 MJ/kg. The ambient conditions are 1.013 bar, 27ºC.

(b) How do you measure air consumption rate of I.C engine in the laboratory? 6 (a) A two stage air compressor compresses air from 1 bar 200C to 42 bar. If the law of

compression is pV1.35 = constant and intercooling is perfect. Find per kg of air (i) the work done in compression. (ii) the mass of cooling water necessary for abstracting the heat in the intercooler, if the temperature rise of the cooling water a 250C.

(b) What are power producing and power absorbing machines? List few of them. 7 (a) A roots blower handles free air of 0.5 m3/s at 1 bar and 270C and delivers air at a pressure of 2

bar. Determine the indicated power required to drive compressor and isentropic efficiency. (b) With the help of neat sketch, explain the working of roots blower. Also show the compression

process in p-V diagram. 8 In an axial flow compressor, the overall stagnation pressure ratio achieved is 4 with overall

stagnation isentropic efficiency 86%. The inlet stagnation pressure and temperature are 1 bar and 320 K. The mean blade speed is 190 m/s. The degree of reaction is 0.5 at the mean radius with relative air angles of 100 and 300 respectively. The work done factor is 0.9. Calculate: (i) Stagnation polytropic efficiency. (ii) Number of stages. (iii) Inlet temperature and pressure. (iv) Blade height in the first stage if the hub-tip ratio is 0.4, mass flow rate is 20 kg/sec

2

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Code: 9A03402

B.Tech II Year II Semester (R09) Regular & Supplementary Examinations, April/May 2013 THERMAL ENGINEERING - I

(Mechanical Engineering) Time: 3 hours Max Marks: 70

Answer any FIVE questions All questions carry equal marks

*****

*****

1 (a) What is the use of air-standard cycle? List some air standard cycles. (b) Discuss the effect of exhaust valve opening time on blow down. 2 (a) What is IC engine? Classify I.C engines. (b) Compare external combustion and internal combustion engine. 3 What are the factors which affects the ignition lag, flame propagation in S.I engines? 4 Explain any three important phases of combustion in C.I engine. 5 (a) Define the terms: brake power, piston speed, brake mean effective pressure and brake thermal efficiency. (b) A two cylinder four stroke engine runs at 240 r.p.m developing a torque of 5.16 kN- m. The bore and

stroke of cylinder are 30 cm and 58.5 cm respectively. Engine runs with gaseous fuel having calorific value of 16.8 MJ/m3. The gas and air mixture is supplied in proportion of 1:7 by volume. The volumetric efficiency is 0.85. Determine (i) The brake power. (ii) The mean piston speed in m/s. (iii) The brake mean effective pressure. (iv) The brake thermal efficiency.

6 (a) With the help of neat sketch explain the working principle of single stage single acing reciprocating air

compressor. (b) A single-stage, double acting compressor has a free air delivery of 14 m3/min, measured at 1.013 bar and

150C. The pressure and temperature in the cylinder during induction are 0.95 bar 150C. The delivery pressure is 7 bar and index of compression and expansion is 1.3. The clearance volume is 5% of the swept volume. Calculate: (i) Indicated power required. (ii) Volumetric efficiency.

7 (a) Define and explain the terms: pressure coefficient and adiabatic coefficient of a centrifugal compressor. (b) A single sided centrifugal compressor is to deliver 14 kg/s of air when operating at a pressure ratio of 4:1

and a speed of 200 rev/s. The inlet stagnation conditions are 288 K and 1.0 bar. The slip factor and power input factor may be taken as 0.9 and 1.04 respectively. The overall isentropic efficiency is 0.80. Determine the overall diameter of the impeller.

8 (a) Define polytropic efficiency of an axial flow compressor and write the expression. (b) A multi stage axial compressor is required for compressing air at 300 K, through a pressure ratio of 4.5 to

1. Each stage is to be a 50% reaction and the mean blade speed of 300 m/s, flow coefficient 0.5, and the stage loading factor 0.3 are taken, for simplicity, as constant for all stages. Determine the flow angles and the total number of stages required if the polytropic efficiency is 85%. Take Cp = 1.005 kJ/kg K and = 1.4 for air.

3

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Code: 9A03402

B.Tech II Year II Semester (R09) Regular & Supplementary Examinations, April/May 2013 THERMAL ENGINEERING - I

(Mechanical Engineering) Time: 3 hours Max Marks: 70

Answer any FIVE questions All questions carry equal marks

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1 (a) Discuss the effect of exhaust valve opening time on blow down. (b) What are the factors that affect the volumetric efficiency of an engine? 2 (a) What are the various components to be lubricated in an engine and explain how it is accomplished? (b) What are the various characteristics of an efficient cooling system in an engine? 3 (a) What do you understand from abnormal combustion in S.I engines? (b) Explain different stages of combustion in S.I engine. 4 (a) What are the factors that affect the combustion process in C.I engines? (b) What is knocking in diesel engine? Explain in detail. 5 (a) A gas engine having a cylinder 250 mm bore and 450 mm stroke has a volumetric efficiency of 80%.

Air-gas ratio equals 9:1, calorific value of fuel 21000 kJ/m3 at NTP. Calculate the heat supplied to the engine per working cycle. If the compression ratio is 5:1, what is the heat value of the mixture per working stroke per m3 of total cylinder volume?

(b) Explain the performance test of an IC engine. Why is it carried out? 6 (a) Derive an expression for minimum work required for two stage reciprocating air compressor with

perfect inter-cooling and neglect clearance volume. (b) A single stage single acting air compressor delivers 14 m3 of free air from 1 bar to 7 bar. The speed

of the compressor is 300 r.p.m. Assuming the compression and expansion is pV1.35 = constant and clearance is 5% of the swept volume, find the diameter and stroke of the compressor. Take stroke length is 1.5 times the bore diameter.

7 (a) What is power input factor and slip factor? (b) A centrifugal compressor running at 9000 r.p.m delivers 600 m3/min of free air. The air is compressed

from 1 bar and 200C to a pressure ratio of 4 with an isentropic efficiency of 0.82. Blades are radial at outlet of impeller and the flow velocity of 62 m/s may be assumes throughout constant. The outer radius of the impeller is twice the inner and the slip factor may be assumed as 0.9. The blade area coefficient may be assumed as 0.9 at the inlet. Calculate, (i) Final temperature of air. (ii) Theoretical power. (iii) Impeller diameters at inlet and outlet. (iv) Breadth of the impeller at inlet. (v) Impeller blade angle at inlet. (vi) Diffuse blade angle at inlet.

8 (a) Define degree of reaction and write the expression for degree of reaction. (b) An axial flow compressor is to have constant axial velocity of 150 m/s and 50% degree of reaction.

The mean diameter of blade ring is 35 cm and speed is 15000 rpm. The exit angles of the blade are 270. Calculate blade angle at inlet and work done per kg of air with the help of velocity triangles.

4

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Code: 9A03402

B.Tech II Year II Semester (R09) Supplementary Examinations January/February 2014 THERMAL ENGINEERING - I

(Mechanical Engineering) Time: 3 hours Max Marks: 70

Answer any FIVE questions All questions carry equal marks

*****

*****

1 (a) Explain in detail the loss due to gas exchange process in gasoline engine. (b) What is the effect of time loss in the mixing of fuel and air and also in combustion in case of I.C engine?

Explain in detail. 2 (a) Explain the working of four stroke engine with a neat sketch. (b) What promotes the development of two stroke engines? (c) Explain briefly the air cooling method in IC engine. 3 (a) What are the various factors that influence the flame speed in SI engine? (b) Explain the effect of turbulence, air-fuel ratio, temperature and pressure on the flame speed in SI engine

combustion. 4 Explain the following terms related to combustion in C.I engines: (a) Delay period (ignition delay). (b) Diesel knocks. (c) Cetane number. 5 (a) How do you measure air consumption rate of I.C engine in the laboratory? (b) A two stroke two cylinder engine runs with speed of 3000 rpm and fuel consumption of 5 litres/hr. The

fuel has specific gravity of 0.7 and air-fuel ratio is 19. The piston speed is 500 m/min and indicated mean effective pressure is 6 bar. The ambient conditions are 1.013 bar, 15ºC. The volumetric efficiency is 0.7 and mechanical efficiency is 0.8. Determine brake power output considering R for gas = 0.287 kJ/kgK

6 (a) What is the optimum pressure ratio for perfect intercooling in between two stages of compression? The

inlet and outlet pressures may be taken as P1 and P3. (b) A single-stage, double acting compressor has a free air delivery of 14 m3/min, measured at 1.013 bar

and 15 . The pressure and temperature in the cylinder during induction are 0.95 bar 15 . The delivery pressure is 7 bar and index of compression and expansion is 1.3. The clearance volume is 5% of the swept volume. Calculate: (i) Indicated power required. (ii) Volumetric efficiency.

7 (a) A roots blower supplies air at the rate of 1.5 kg/s. The pressure ratio of the blower is 2.5:1 with an intake

pressure and temperature of 1.013 bar and 27 respectively. Find the power required to drive the blower.

(b) Explain the working of vane type blower and show the compression process in p-v diagram. 8 (a) Compare the axial flow compressor with centrifugal compressors. (b) An axial flow compressor stage has a mean diameter of 600 mm and runs at 12000 rpm. Mass flow rate

through the compressor is 60 kg/s. Determine the power required to drive the compressor and degree of reaction if the air angle is 15o. The vane angle at inlet and exit are equal to 45o and 25o respectively.

R09