Applied Thermodynamics - May 2014

Mechanical Engg (Semester 4)

TOTAL MARKS: 100
TOTAL TIME: 3 HOURS (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 classification of I.C. Engine. State any 4 applications of I.C. Engines.(6 marks) 1 (b) Explain detonation in S.I. Engine and factors affecting detonation.(6 marks) 2 (a) Explain with neat sketch valve timing diagram of 4-S petrol engine.(6 marks) 2 (b) Draw and explain with neat sketch simple carburettor.(6 marks)

Answer any one question from Q3 and Q4

3 (a) Compare combustion in S.I. and C.I. Engine (6 points).(6 marks) 3 (b) During trial on single cylinder 4-S oil engine, following results were obtained:
Cylinder Diameter = 20 cm, Stroke = 2D, Mean Effective pressure = 6 bar, Torque = 407 N-m, Speed = 250 RPM, Oil Consumption = 4 kg/hr, Calorific Value of Fuel = 43 MJ/kg, Cooling water flow rate = 4.5 kg/min, Air used per kg of fuel = 30 kg, Rise in cooling water temperature = 45°C, Temperature of exhaust gases = 420°C, Room Temperature = 20°C, Mean specific heat of exhaust gas = 1 kJ/kg K, Specific heat of water = 4.187 kJ/kg K, Draw heat balance sheet for the test in kJ/hr. Calculate Mechanical efficiency.(6 marks) 4 (a) What are the requirements of a good combustion chamber design in C.I. engines (6 valid points).(6 marks) 4 (b) The air flow to 4 cylinder 4-S gasoline engine was measured by means of 8 cm diameter sharp edge orifice with C d = 0.65. During a test the following data was recorded: Bore = 10 cm, Stroke = 15 cm, Engine speed = 2500 RPM, Brake power = 36 kW, Fuel Consumption = 10 kg/hr, Calorific Value of fuel = 42 MJ/kg, Pressure drop across orifice = 4 cm of water, Atmospheric Temperature and pressure are 17°C and 1 bar resp. Density of air = 1.2 kg/m³. Calculate:
i) Brake thermal efficiency
ii) Brake Mean Effective Pressure
iii) Volumetric Efficiency.(6 marks)

Answer any one question from Q5 and Q6

5 (a) Explain with neat sketch Thermostatic cooling system used in automobiles.(7 marks) 5 (b) Describe with schematic diagram working of electric starting system.(6 marks) 6 (a) Explain with neat sketch EGR system.(7 marks) 6 (b) Compare magneto-ignition system and Battery ignition system (6 points).(6 marks)

Answer any one question from Q7 and Q8

7 (a) Explain roots blower compressor with neat sketch.(6 marks) 7 (b) A reciprocating compressor of single stage, double acting type delivers 20m³/min when measured at free air condition of 1 bar, 27°C. The compressor has pressure ratio of 7 and the conditions at the end of suction are 0.97 bar, 35°C. Compressor runs at 240 RPM with clearance volume of 5% of swept volume. The L/D ratio is 1.2. Determine the volumetric efficiency and dimensions of cylinder and isothermal efficiency taking the index of compression and expansion as 1.25. Also show the cycle on P-V diagram.(6 marks) 8 (a) Explain the methods of improving isothermal efficiency of reciprocating compressors with P-V diagram.(6 marks) 8 (b) A three stage reciprocating air compressor compresses air from 1 bar and 170 C to 35 bar. The law of compression is PV1.25 = C and is same for all stages of compression. Assuming perfect intercooling, neglecting clearance, find the minimum power required to compress 15 m³/min of free air. Also find the intermediate pressures.(7 marks)