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Posted By: yamini Member Level: Gold Posted Date: 13 May 2008
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2007 Jawaharlal Nehru Technological University B.Tech Mechanical Engineering II II ME thermal enginnering aug/sep 2007 set III Question paper
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Code No: R05220304 Set No. 3
II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2007
THERMAL ENGINEERING-I
( Common to Mechanical Engineering and Automobile Engineering)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
? ? ? ? ?
1. (a) Explain the principle operation of an I.C .Engine with neat sketch?
(b) Why the exhaust valve is opened before BDC and closed after TDC? [8+8]
2. (a) Describe the mixture requirement in S.I. Engine for di erent speed conditions.
How to achieve above requirements from the carburetor.
(b) What are di erent types of combustion chambers used in S.I.Engine? [10+6]
3. (a) What are di erent four stages of combustion in C.I. Engine? Explain salient
features.
(b) How to minimize diesel knock? Explain di erent controlling methods. [8+8]
4. (a) List the parameters by which performance of an engine is evaluated.
(b) Find the bore of the single-cylinder diesel engine working on the four-stroke
cycle and delivers 40 kW at 200 rpm from the following date:
Compression ratio : 14:1
Fuel cut-o : 5% of stroke
Index of compression curve : 1.4
Index for expansion curve : 1.3
Pressure at beginning of compression : 1 atm
Ratio of stroke to bore : 1.5 to 1. [8+8]
5. A single acting two stage compressor with complete inter cooling delivers 6 kg/min
of air at 16 bar. Assuming an intake at 1 bar and 150C and compression and
expansion with the law pV1.3 = C. Calculate.
(a) Power required to run the compressor at 420 rpm
(b) Isothermal eciency
(c) Free air delivered per sec.
(d) If clearance ratios for LP and HP cylinder are 0.04 and 0.06, calculate volu-
metric eciency and swept volume for each cylinder.
(e) Net heat transferred in LP and HP cylinders during compression and also in
the intercooler. Assume R = 0.287 kJ/kg K, Cv = 0.71 kJ/ kg K. [16]
6. The conditions of air at the entry of an axial compressor stage are p1 = 768 mm
Hg and T1 = 314 K. The air angles are ß1 = 510, ß2 = 90, a1 = a3 = 70 The
mean diameter and peripheral speed are 50 cm and 100 m/s, respectively. Mass-
flow rate through the stage is 25 kg/s; the work-done factor is 0.95 and mechanical
eciency 92%. Assuming a stage eciency of 88% determine:
(a) air angle at the stator entry,
(b) blade height at entry and the hub-tip diameter ratio,
(c) stage loading coecient,
(d) stage pressure ratio, and
(e) the power required to drive the stage. [16]
7. (a) In respect of a reciprocating refrigerant compressor, define the team ‘volumet-
ric eciency’ and discuss the factors which e ect it.
(b) A dense air refrigerating system operating between pressures of 16 bars and
4 bars is to produce 10 tons of refrigeration. The air temperature leaving the
refrigerating coils is-70C and the air temperature leaving the air cooler is 170C.
Assuming no losses and no clearance, calculate the mass of air in circulation
(kg/min), power required (kW), and piston displacement for the compressor
(m3 /min). For air Cp= 1.005 kJ/kg K, R=0.287 kJ/kg. K. [16]
8. (a) What is the bypass factor ? Explain its usefulness.
(b) The air-handling unit of an air-conditioning plant supplies a total of 4500 c.
mm. of dry air which comprises by weight 20 per cent fresh air at 40 C DBT
and 270C WBT and 80 per cent recirculated air at 250C DBT and 50 per cent
RH. The air leaves the cooling coil at 130C saturated state. Calculate the
total cooling and room heat gain. [16]
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