Internal Combustion Engine - Dec 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 the following any four:-

1 (a) Explain the main functions of fuel supply system in C.I. engines.(5 marks) 1 (b) Explain the phenomenon of pre-ignition. Explain how pre-ignition leads to detonation and vice versa.(5 marks) 1 (c) Explain how induction swirl is created? What are the requirements of injector for this type of swirl?(5 marks) 1 (d) Describe the phenomenon of knocking in S.I. engines with the help of P-? and P-V plots. (5 marks) 1 (e) Give a brief classification of diesel injection system with explanation of any one system.(5 marks) 2 (a) A four cylinder, four stroke, square engine running at 2400rpm has a carburettor venturi with a 30m throat. The engine cylinder bore is 100mm and volumetric efficiency 75%. Take density of air as 1.15kg/m³ and coefficient of air flow, Cd as 0.75. Neglecting compressibility of air, calculate the suction at the throat.(10 marks) 2 (b) Define the following terms and explain their significance. Also name the tests used to evaluate them for:
i) Constant speed
ii) Variable speed engines
iii) Indicated power
iv) Mechanical efficiency
v) Brake thermal efficiency
vi) Frictional power(10 marks) 3 (a) The following observations were made during a test on a diesel engine:-
Brake power of engine=31kW
Fuel consumption=10kg/h
Flow rate of cooling water=530kg/h
Rise in temperature of cooling water=50°C
Calorific value of fuel=44000kJ/kg
Exhaust gases are passed through an exhaust gas calorimeter. Flow rate of water through the calorimeter is 450kg/h and its rise in temperature is 40°C. Exhaust gases leave the calorimeter at 90°C. Assuming the engine used A/F ratio of 20:1. Prepare a heat balance sheet on minute basis and percentage basis.(10 marks) 3 (b) Explain:
i) Octane number
ii) Cetane number(10 marks) 4 (a) Determine the diameter of a fuel orifice for a four stroke engine which develops 15kW at 2000rpm. Fuel consumption is 0.24kg/kW-h of a fuel of 32°C API. The duration of fuel injection is 30° of crank rotation. Fuel injection pressure is 130bar and cylinder pressure is 45bar. Assume velocity coefficient 0.9 and specific gravity of fuel is given by the relation:-(10 marks) 4 (b) Explain the function of any two with neat sketches:-
i) Air bleed jet
ii) Emulsion tube
iii) Anti-dieseling system
iv) Economiser system(10 marks) 5 (a) What are the objectives of supercharging? What are the limitations of supercharging? Explain the term charge cooling and how it is achieved in a turbocharged engine.(10 marks) 5 (b) Explain the types of combustion chambers used in S.I. engines and compare them why the maximum diameter of S.I. engine combustion chambers is limited?(10 marks) 6 (a) A fuel has the following percentage composition by mass:-
C=85%, H₂=15%
Determine:
i) The stoichiometric mass of air required for complete combustion of fuel.
ii) The percentage composition by mass of dry products of combustion.
Air contains 23.2% oxygen by mass.(10 marks) 6 (b) Explain with neat sketches the working of a battery ignition and magneto ignition and compare their advantages and disadvantages.(10 marks)

Write short notes on any four:-

7 (a) Requirements of spark plug in S.I. engine with neat sketch.(5 marks) 7 (b) Alternative fuels used in I.C. engines.(5 marks) 7 (c) Wankel Engines.(5 marks) 7 (d) MPFI for S.I. engines.(5 marks) 7 (e) Engine cooling systems.(5 marks) 7 (f) SAE ratings of lubricants.(5 marks)