33715(37)
B.E.(Fifth semester)Examination
NOV.-DEC.,2008
(Mechanical engg. branch)
INTERNAL COMBUSTION ENGINES
Time allowed : Three hours
Maximum Marks : 80
Minimum Pass Marks : 28
Note : (1) Attempt all questions. part (a) of all questions are compulsory
(2) Answer any two parts from part (b), (c) and (d). Explain your
answer by means of neat sketches wherever it is necessary.
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1. (a) What are the two general classes of combustion engines and how do they basically differ in principle? 2
(b) Draw actual valve timing diagram of a petrol engine. Explain why the opening and closing of inlet and exhaust valves are not at the dead centre position of the piston and give reasons for spark advance. 7
(c) What are the reasons for differing the actual p-v diagram from ideal diagram? Discuss loss due to variation of specific heat and pumping loss. 7
(d) What are the objects of supercharging? Explain the thermodynamic cycle of conventional and super charged engine on p-v diagram for C.I. Engine. 7
2. (a) What are the two basic requirements of an I.C. engine fuel ? 2
(b) Discuss the effect of fuel structure on:
- Knocking
- Volatility and
- Heating value of fuel.
(c) A producer gas has the following percentage analysis by volume: H2-10, CO-20, CH4-2, CO2-6 & N2-62.
- Calculate the stoichiomtric air for complete combustion of 1 m3 of gas.
- If 20% excess air is supplied, calculate the percentage composition by volume of the product of combustion.
(d) Explain the knocking combustion in SI and CI engines with the help of pressure-crank angle diagram.
3. (a) What are the major difficulties to be faced if a simple carburettor is used in an automobile engine ?
(b) Discuss the air fuel mixture requirements for various states of engine operations. 7
(c) What is petrol injection? Discuss the advantage and dis advantage of petrol injection system with conventional carburettor system.
(d) The venturi of a simple carburettor has a throat diameter of 20 mm and thecoefficient of air flow is 0.85. the fuel orifice has a diameter of 1.25 mm and coefficient of fuel flow is 0.66. petrol surface is 5 mm below the throat . find :
- The air- fuel ratio for a pressure drop of 0.07 bar when nozzel lip is neglected.
- The air fuel ratio when the nozzel lip is taken into account
Take density of air and fuel as 1.2 and 750 kg/m3 respectively.
4. (a) Why cooling of I.C. engines is essential ?
(b) Explain the working of a megneto ignition system with the help of neat sketch. Discuss its relative merits and demerits over battery ignition system.
(c) Describe with help of suitable sketches
- jerk pump system
- common rail system
- distributor system.
Discuss their relative advantages and disadvantages.
(d) Discuss the functions of lubricant in an engine and describe a typical mist lubrication system used for a two stroke engine with its advantage and disadvantages.
5. (a) Show by a diagram the energy flow in a reciprocating internal combustion engine.
(b) What are the various methods of measuring friction power? Describe the Willan's line method.to which type of engine its applicable?
(c) the air flow to four cylinder, four stroke diesel engine is measured by means of a 5cm diameter orifice, having a coefficient of discharge of 0.6. During a test on the engine the following data were recorded:
Bore-10.5 cm, stroke -12.5 cm, engine speed-1200 rpm,break torque-147Nm, fuel consuption-5.5 kg/hr, caloric value of fuel- 43100 kj/kg, Head across orifice-5.7 cm of water, ambient temprature and pressure-20 c and 1.013 bar respectively.
Calculate
- Break power
- Break thermal efficiency
- The volumetric efficiensy
(d) Discuss the various methods of control for exhaust emission from petrol engines.
