337512(37)
B.E (Fifth Semester) Examination,
NOV.-DEC., 2007
(Mechanical Branch)
INTERNAL COMBUSTION ENGINES
Time allowed : Three Hours
Maximum Marks : 80
Minimum Pass Marks : 28
Note :- Attempt (a) and two parts out of (b) , (c) and (d) of each question . Marks are iven in the margin.
1. (a) Compare two sroke cycle engine and four stroke cycle engine. What are their applications?
(b) Draw the valve timing diagram of a four stroke petrol engine. Explain why the valves are openedbefore dead centres and closed after dead centres.
(c) What are the reason for differing the actual p-V diagram from ideal diagram? Discuss variation of specific heat and exhaust blow down loss.
2. (a) Explain with the help of p-Q diagram the stages of combustion in S.I. engine. In what way detonation differs from preignation.
(b) What is ASTM distillation curve? Discuss the effect of volatility on the following :
Carburrettor icing
Vapour lock
(c) Explain the effect of fuel structure on knocking. Define Octane number, HUCR and Cetane number.
3. (a) Draw the neat sketch of a simple carburettor and explain its working. What are the drawbacks of a simple carburettor?
(b) What is petrol injection system? What are its marits and demerits?
(c) The venturi of simple carburretor has a throat diameter of 20 mm and the coefficient of air flow is 0.85. The fuel oriffice has a diameter of 1.25 mm and the coefficient of fuel flow is ).66. The petrol surface is 5mm below the throat. Find :
the air fuel ratio for a pressure drop of ).)7 bar when the nozzle lip is neglected;
the air fuel ratio when the nozzle lip is taken into account.
Take density of air and fuel as 1.2 and 750 kg/m3 respectively.
4. Write notes on any four of the following :
- Battery ignition system
- Spark plug heat range
- Working of fuel injector
- Merits and demerits of air and water colling systems
- Governing of I.c. Engines
- Wet sump lubrication method
5. (a) Draw the following performance curves of a S.I. engine and comment on nature of curve.
Indicated power Vs speed at full throttle.
Specific fuel consumption Vs speed at full throttle
(b) Describe the "Morse Test". What are the assumptions made in this test? What precautions should be taken in performing this test?
(c) Calculate bore and stroke of a six cylinder, four stroke petrol engine for the following data :
Compression ratio = 6, bp = 312 kW; N = 2500 r.p.m. stroke = 1.25 times the bore, mechanical efficiency 0.82; imep = 10 bar; relative efficiency = 0.5 and calorific value of fuel = 43960 kJ/kg.
Also calculate the fuel consumption in kg/min.
