Internal Combustion Engine - May 2013

Mechanical Engineering (Semester 6)

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 four of the following:-

1 (a) State the assumptions in an Air Standard cycle and explain the deviations of Fuel-Air Cycle with reference to it.(5 marks) 1 (b) Explain why a simple carburettor cannot meet the various engine requirements.(5 marks) 1 (c) Compare the phenomenon of knock in C.I. and S.I. engines.(5 marks) 1 (d) Distinguish between four stroke and two stroke engines.(5 marks) 1 (e) Compare air-cooling with water-cooling used in an I.C. engine.(5 marks) 1 (f) Write a note on rating of fuels for I.C. engines.(5 marks) 2 (a) Explain with a sketch the construction and working of a Solex carburettor.(10 marks) 2 (b) Describe the phenomenon of combustion in C.I. engine and explain in detail the various stages in it.(10 marks) 3 (a) Draw the theoretical and actual valve timing diagram for a four stroke C.I. engine and discuss in brief the deviations between the two.(8 marks) 3 (b) An 8 cylinder, 4 stroke diesel engine has a power output of 368kW at 800rpm. The fuel consumption is 0.238kg/kW-h. The pressure in the cylinder at the beginning of injection is 35bar and the maximum cylinder pressure is 60bar. The injection of fuel is expected to be at 210bar and the maximum pressure at the injector is set to be at about 600bar. Calculate the orifice area required for each injector if the injection takes place over 12° crank angles. Assume the coefficient of discharge for the injector is 0.6, specific gravity of fuel is 0.85 and the atmospheric pressure is 1.013bar. Take the effective pressure difference to be the average pressure difference during the injection period.(12 marks) 4 (a) The venturi of a simple carburetor has a throat diameter of 20mm and the coefficient of air flow is 0.85. The fuel has an orifice diameter of 1.25mm and the coefficient of fuel flow is 0.62. The petrol surface is 6mm below the throat. Find:
i) The air-fuel ratio for a pressure drop of 0.07bar when the nozzle tip is neglected.
ii) The air-fuel ratio when the nozzle tip is taken into account
iii) The minimum velocity of air required to start the fuel flow when the nozzle tip is provided.
Take density of air and fuel as 1.2 and 750 kg/m³ respectively.(12 marks) 4 (b) What do you understand by supercharging? What are its advantages and limitations?(8 marks) 5 (a) The average indicated power developed in a C.I. engine is 13kW/m³ of free air induced per minute. The engine is a 3litre four stroke engine running at 3500rpm and has a volumetric efficiency of 81% referred to free air conditions of 1.013bar and 15°C. It is proposed to fit a blower driven mechanically from the engine. The blower has isentropic efficiency of 72% and works through a pressure ratio of 1.72. Assume that, at the end of induction the cylinders contain a volume of charge equal to the swept volume at the pressure and temperature of the delivery from the blower.
Calculate the increase in brake power to be expected from the engine. Take all mechanical efficiencies as 78%.(12 marks) 5 (b) Explain with a neat sketch the working of a dry sump lubrication system.(8 marks) 6 (a) Explain with a neat sketch the battery ignition system and elaborate on the significance of individual components.(8 marks) 6 (b) In a test on a single cylinder 4 stroke diesel engine with bore 400mm and stroke 450mm, the following observations were made:
Duration of test=1hr
Fuel consumption=7.5kg
C.V. of fuel=44500kJ/kg
Total revolutions=12000/hr
Indicated mean effective pressure=3.75bar
Net brake load=1500N
Brake drum diameter=180cm
Rope drum diameter=3cm
Jacket cooling water=600kg
Rise in cooling water temp.=42°C
Total air consumption=361kg
Exhaust gas temperature=300°C
Room temperature=20°C
Specific heat of exhaust gases=1.01 kJ/kg-K
Calculate:
i) Mechanical efficiency
ii) Indicated and brake thermal efficiency
iii) Draw the heat balance sheet on minute basis(12 marks)

Write short notes on any four:-

7 (a) Wankel Engine.(5 marks) 7 (b) Mist lubrication system.(5 marks) 7 (c) Magneto ignition system.(5 marks) 7 (d) Thermosyphon cooling.(5 marks) 7 (e) Methods of fuel injection.(5 marks) 7 (f) Exhaust Gas Recirculation.(5 marks)