Internal Combustion Engine - May 2012

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. 1 (a) Differentiate between four stroke and two stroke engines.(5 marks) 1 (b) Draw a heat balance sheet and show various heat inputs and losses in it.(5 marks) 1 (c) Draw the circuit diagram and explain the working of a battery ignition system.(5 marks) 1 (d) With a neat sketch describe a simple carburettor.(5 marks) 2 (a) Describe mist lubrication.(5 marks) 2 (b) A test of one hour duration was conducted on a single cylinder engine having a bore of 300mm and stroke of 450mm. Fuel consumed is 8.8kg at an average speed of 200rpm. The mean effective pressure of the engine 5.8bar and calorific value of fuel is 41800J/kg. The brake friction load is 1860N for a brake wheel of diameter 1.22mm. Quantity of cooling water consumed during the test is 650kg with a rise in temperature of 22°C.
Draw the heat balance sheet on hourly and percentage basis and also calculate:
i) Mechanical Efficiency
ii) Brake Thermal Efficiency(15 marks) 3 (a) Explain the various stages of combustion in S.I. engines.(8 marks) 3 (b) A S.I. engine consumes 7.2kg/hr of fuel having a specific gravity of 0.75 at 27°C. A simple carburettor having a choke tube of 24mm and supplying A/F ratio of 15 is attached to it. If the height of top of the jet above the petrol level is 4.2mm, calculate the diameter of the fuel jet.
Take coefficient of discharge for air=0.8 and for fuel=0.7. Atmospheric pressure is 1.013bar.(12 marks) 4 (a) Describe the various losses and its effect in fuel-air cycle analysis.(6 marks) 4 (b) A C.I. engine having a stroke length of 200mm and bore of 160mm is having a fuel consumption rate of 2.8kg/h at 400rpm. The engine is connected to brake dynamometer having a drum diameter of 1.2m. The load applied on the brake drum is 370N and the spring balance reading is 50N. An indicator diagram mechanism is also connected to this engine having a spring constant of 1bar/mm. The length of the indicator diagram is 40mm and the area is 300mm².
Take calorific value of fuel as 41800kJ/kg and engine as single cylinder, 4-stroke.
Calculate:
i) Indicated mean effective pressure
ii) Brake power
iii) Brake mean effective pressure
iv) BSFC
v) Brake and indicated thermal efficiencies(14 marks) 5 (a) What are the constituents of the exhaust gases of S.I. engines? Explain any method to control any one of them.(8 marks) 5 (b) Explain the working of thermostatic cooling system.(8 marks) 5 (c) Define: Octane Number and Cetane Number.(4 marks) 6 (a) Enlist the various losses occurring in actual cycles. Describe exhaust blowdown and pumping losses in detail.(8 marks) 6 (b) A 6 cylinder 4 stroke C.I. engine develops 220kW at 1500rpm, with brake specific fuel consumption of 0.273kg/kW-h. Determine the size of the single hole injector nozzle if the injection pressure is 160bar and the pressure in the combustion chamber is 40bar. The period of injection is 30° of crank angle. Specific gravity of fuel is 0.85 and the orifice discharge coefficient is 0.9.(12 marks)

Write short notes on any four:-

7 (a) Non-conventional fuels.(5 marks) 7 (b) Wankel engines.(5 marks) 7 (c) Stratified Charge Engines.(5 marks) 7 (d) Exhaust Gas Recirculation.(5 marks) 7 (e) Electronic Ignition System.(5 marks) 7 (f) Scavenging.(5 marks) 7 (g) Air-Box Method.(5 marks)