Question Paper: Applied Thermodynamics : Question Paper Jun 2015 - Mechanical Engineering (Semester 4) | Pune University (PU)

Applied Thermodynamics - Jun 2015

Mechanical Engg (Semester 4)

(1) Question 1 is compulsory.
(2) Attempt any four from the remaining questions.
(3) Assume data wherever required.
(4) Figures to the right indicate full marks.

Answer any one question from Q1 and Q2

1 (a) Explain with the help of a P-V diagram the loss due to variation of specific heats in an Otto cycle.(6 marks) 1 (b) With a neat sketch explain the working principle of simple carburettor.(6 marks) 2 (a) Draw ideal and actual valve timing diagram for four stroke S.I. engine.(6 marks) 2 (b) Explain the different stages of combustion in S.I. engine.(6 marks)

Answer any one question from Q3 and Q4

3 (a) Explain the various factors that influence the delay period in C.I. engine.(6 marks) 3 (b) In a test of a four-cylinder four-stroke petrol engine of 75 mm bore and 100 mm stroke, the following results were obtained at full throttle at a constant speed and with a fixed setting of the fuel supply of 0.082 kg/min:
BP with all cylinders working = 15.24 kW
BP with cylinder No. 1 cut-off = 10.45 kW
BP with cylinder No. 2 cut-off = 10.38 kW
BP with cylinder No. 3 cut-off = 10.23 kW
BP with cylinder No. 4 cut-off = 10.45 kW

Estimate: (1) Total indicated power of the engine
(2) Total friction power,
(3) Indicated thermal efficiency of the engine
If the calorific value of the fuel is 44 MJ/kg.
(7 marks)
4 (a) Explain with figures various types of combustion chambers used in CI engines.(6 marks) 4 (b) During the trial of a single cylinder, four-stroke oil engine, the following results were obtained:

Cylinder diameter =20 cm
Stroke =40 cm
Mean effective pressure =6 bar
Torque = 407 Nm
Speed =250 r.p.m.
Fuel consumption = 4 kg/h
Calorific value of fuel = 43 MJ/kg
Cooling water flow rate = 4.5 kg/min
Air used per kg of fuel = 30 kg of air/kg of fuel
Rise in cooling water temperature = 45oC
Temperature of exhaust gases = 420oC
Room temperature = 20oC
Mean specific heat of exhaust gas = 1 kJ/ kgK
Specific heat of water = 4/18 kJ/kgK

Find IP, BP and draw heat balance sheet for the test.(7 marks)

Answer any one question from Q5 and Q6

5 (a) Explain with neat sketch pressurized dry sump lubrication system.(6 marks) 5 (b) Discuss the effect of A:F ratio on emission of:
i) Unburnt HC
ii) CO
iii) NOx.
(6 marks)
6 (a) Explain battery ignition system with neat diagram.(6 marks) 6 (b) Explain exhaust gas recirculation method used to control NOx emissions.(6 marks)

Answer any one question from Q7 and Q8

7 (a) What are the advantages of multi-staging in reciprocating air compressor?(6 marks) 7 (b) During an experiment on reciprocating air compressor the following observations are being taken:

Barometer reading = 75.6 cm Hg
Manometer reading across orifice = 13 cm Hg
Atmospheric temperature = 25oC
Diameter of orifice = 15 mm
Coefficient of discharge across the orifice =0.65
Take density of Hg = 0.0135951 kg/cm3

Determine the volume of free air handled by compressor in m3/min.(7 marks) 8 (a) Draw isothermal, polytrophic and isentropic compression on P-V and T-s diagram and compare the three works.(6 marks) 8 (b) Determine the minimum number of stages required in an air compressor which admits air at 1 bar 27°C and delivers at 180 bar. The maximum discharge temperature at any stage is limited to 150°C. Consider the index for polytropic compression as 1.25 and perfect and optimum inter-cooling in between the stages. Neglect the effect of clearance.(7 marks)

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