2. (a) An engine fitted with a single jet carburettor having a jet diameter of 1.25 mm has a fuel consumption of 6 kg/hr. The specific gravity of fuel is 0.7. The level of fuel in the float chamber is 5mm below the top of the jet when the engine is not running. Ambient conditions are 1 bar and 17°C. The fuel jet diameter is 0.6 mm. The discharge coefficient of air is 0.85. Air-fuel ration is 15. Determine the critical velocityof flow at throat and the throat diameter. Exprexx the pressure at throat in mm of water column. Neglect compressibility effect. Assume discharge coefficient of fuel flow is 0.60. 15
(b) Find the percentage increase in the efficiency of a Diesel Cycle having a compression ratio 'r' of 16 and cut off ratio 'r' is 10% of the swept volume, if Cv decrease by 2%. Take Cv← 0.717 kJ/kg °K and γ← 1.4. 15
(c) Explain the knocking phenomenon in a CI engine. Compare it with that of SI engines. Discuss the effect of operating variables on delay period and diesel knock. 10
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Engineering Services Examination 2011:Mechanical Engineering Question Paper I (Conventional)