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Friday, 11 January 2013

Internal combustion engines – for B.E/B.Tech model question paper



1(a) Explain with suitable sketches, the working of a four-stroke spark-ignition engine. (6 Marks)
(b) Define mean effective pressure. What is its relevance in reciprocating engines? (4 Marks)
(c) What are the characteristics of constant volume fuel-air cycle? (6 Marks)
(d) A diesel engine develops 5 kW. Its indicated thermal efficiency is 30% and mechanical efficiency 57%. Estimate the fuel consumption of engine in (a) kg/hr, (b) litres/hr, (c) indicated specific fuel consumption, and (d) brake specific fuel consumption. (4 Marks)
2(a) Explain the term ‘burning time loss’ with the help of p-V diagram. (4 Marks)
(b) Discuss the general principles of SI engine combustion chamber design. (6 Marks)
(c) Discuss the variables affecting the delay period. (4 Marks)
(d) In a bomb calorimeter test on petrol, the HCV was determined and found to be 46900 kJ/kg. If the fuel contains 14.4% H2 by mass, calculate the LCV. Given ufg at 250C for H2O = 2304.4 kJ/kg. (4 Marks)
3(a) What are the factors which affect the process of carburetion? (4 Marks)
(b) Distinguish between continuous injection system and timed injection system. (6 Marks)
(c) Compare the burning rates in petrol and diesel engines. (4 Marks)
(d) A 6-cylinder 4-stroke S.I. engine having a piston displacement of 700 cm3 per cylinder developed 78 kW at 3200 r.p.m and consumed 27 kg of petrol per hour. The calorific value of petrol is 44 MJ/kg. Estimate the volumetric efficiency of the engine if the air-fuel ratio is 12 and the intake air is 0.9 bar, 320C.  Also determine the brake thermal efficiency and the brake torque. (6 Marks)
4(a) Describe a battery ignition system with the help of a sketch. (6 Marks)
(b) What is a Texaco ignition system? Mention its advantages. (4 Marks)
(c) What is the significance of flash and fire points of a lubricant. (6 Marks)
(d) A petrol engine with indicated thermal efficiency of 30% has an fp of 18 at 1500 rev/min and 45 kW at 2500 rev/min. If the bhp required at each speed is 75 kw and the calorific value of the fuel is 44000 kJ/kg, calculate the bsfc at both speeds, assuming indicated thermal efficiency to be same at both speeds. (4 Marks)
5 (a) Why is over-cooling in an engine harmful? (4 Marks)
(b) Describe with a sketch the construction and working of a thermostat. (6 Marks)
(c) Explain the scavenging process in two-stroke engine. What is meant by blowdown? (6 Marks)
(d) Explain pulse turbocharging. (4 Marks)
6 (a) Describe with a sketch, the principle of eddy current dynamometer. (6 Marks)
(b) What are reduction mechanisms for taking indicator diagrams? Describe with sketches the important types of reduction mechanisms. (6 Marks)
(c) What is a flame ionization detector? (4 Marks)
(d) A test on a two-stroke single cylinder oil engine gave the following results: Cylinder bore=200 mm, engine stroke=250 mm, indicated mean effective pressure=4.5×102 N/m2, fuel consumption=7kg/h, calorific value of fuel=43500 kJ/kg, engine speed=180 rev/min. Calculate the indicated power and indicated thermal efficiency. (4 Marks)
7 (a) Describe with a sketch, a dual-fuel engine and comment on its performance. (6 Marks)
(b) Discuss the performance of multi-fuel engine on various fuels. (4 Maks)
(c) What is meant by crankcase blowby? How it can be controlled? (6 Marks)
(d) Compare diesel engine and gasoline engine emissions. (4 Marks)
8 (a) What are the important methods of charge stratification? (4 Marks)
(b) Discuss with the help of a sketch, the governance of Stirling engine. (6 Marks)
(c) Discuss some applications of Wankel RC engine. (4 Marks)
(d) A gas turbine cycle takes in air at 250C and atmospheric pressure. The compression pressure ratio is 4. The compressor efficiency is 75%. The inlet temperature to turbine is limited to 7500C. What turbine efficiency would give overall cycle efficiency 0%.  (4 Marks)

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