,17S·mk : 1stl-lt-t t.

Con. 3798-11. (REVISED' COURSE) RK-2562

.(3 Hours) [Total lV!arks : 100

N.B. (1) Question No.1 is compulsory.(2) Answer any four questions from Question Nos. 2 to 7.(3) Assume suitable data if necessary and state it clearly.(4) Answers should be written together, and one below the other.

1. State whether following statements are true or false and justify (any four) :-. 20(a) Four stroke engines requires more flywheel size as compared to two stroke

engines.(b) Choke in a carburetor is used during idling.(c) Larger the ignition delay lesser the chances of detonation in C.!. Engine

and smaller the ignition delay more the- chances of detonation in S.1.Engine.(d) Converting a naturally aspirated engine into supercharged engine requires

reduction of compression ratio and increase of valve overlap.(e). Larger the octane number more the chances of detonation and vice versa.(f) Mist type of lubrication system can be used in large capacity engines. .

2. (a) The air fuel ratio of a diesel engine is 29 : 1. If the compression ratio is 16 : 1 12and the temperature at the end of compression is 900 K, find at what cylinder

. volume the combustion is complete? Express this volume as a percentage ofstroke. Assume that the combustion begins at the top dead center and takesplace at constant pressure. Take calorific value of fuel as 42000 kJ/kg andR = 0·287 kJ/kg K. The specific heat at constant volume varies w.r. t. temperaturein the relation Cv = 0·709 + 0·000028 T kJ/kg K.

(b) Explain with neat sketch an Electronic Ignition system. 8

3. (a) A single cylinder four stroke oil engine develops 20 kW at 1200 rpm. Its specific 10fuel consumption is 300 gms/kW-hr. The fuel density is 860 kg/m3. The fuelinjection is carried out during 30 degrees of rotation of crank. The average injectionpressure and pressure in the combustion chamber of the engine are 120 barand 30 bar respectively. Find the diameter of nozzle hole if four holes are usedon the nozzle .. Take coefficient of discharge of fuel nozzle = 0·65.

(b) Define the following wing terms in relation to an internal combustion engine with 10their significance:

(i) Brake specific fuel consumption(ii) Brake mean effective pressure(iii) Brake thermal efficiency(iv)· Volumetric efficiency.

4. (a) A supercharged four stroke diesel engine is used to drive an air compressor. 12The air is taken inside the compressor at 20°C and its discharqe is passedthrough a water cooler. The air comes out from cooler at 60°C and l·75 bar.A part of the air coming outfrom cooler is'used to supercharge the engine. Thevolumetric efficiency 'of the engine is 80% on the basis' of inlet conditions, 'The

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176·mk : 1 tHf·11.

Con. 3798"RK •.2562~11. 2·

engine has 6 cylinders with its diameter of 90 mm and stroke of 120 mm. Theengine delivers the output torque of 150 N-m at 2000 rpm. Assuming mechanicalefficiency of 80%, find :-

(I) IMEP of engine(ii) The air used by engine per minute(iii) The amount of air compressed in kg/min.

The amount of heat removed from the compressed air in the water cooler is1350 kJ/min.

(b) Write a note on nonconventional fuels for internal combustion engines. 10

5. (a) Power output of a six cylinder four stroke engine is absorbed by a water brake 12dynamometer for which the law is WN/20000, where W is the brake load in 'N'

-and N is in rpm. The air consumption is measured by an air box method withsharp edged orifice system. Following are the readings obtained :-

Orifice diameter = 30 mmBore = 100 mmStroke = 120 mmBrake Load = 560 NC and H ratio by mass = 83/17Coefficient of discharge = 0·6Ambient Pressure = 1 barPressure drop across orifice = 14·5 cm of HgTime take for 100 cc fuel = 20 secondsConsumptionAmbient TemperatureFuel Density

Calculate : (1) Brake power(2) Brake Torque(3) BSFC(4) Volumetric Efficiency(5) The Percentage of Excess Air(6) BMEP.

(b) "A good CI engine fuel is a bad SI engine fuel and vice versa". Discuss thevalidity of this statement with respect te eight factors to reduce knocking in SIand CI engines.

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6. (a) Explain with neat sketches working of idling system and .cold starting system 8used in modern carburetor.

(b) Compare phenomenon of detonation in SI and CI engines. 8(c) Explain why it is difficult to design high speed diesel engines. 4

7. Write notes on any four :- 20(a) Turbo charging vIs Supercharging(b) Properties of Lubricants(c) Wankel Engine(d) Air cooling vIs Water cooling(e) Rating of Fuels.

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