JNTU
JNTU B.Tech III THERMAL ENGINEERING Previous Question Paper (November/December - 2018 - R15)
Part A is compulsory. Answer any one full question from each unit in Part B.
Part A
Define two-stroke and four stroke engines.
Answer
A two-stroke engine is an internal combustion engine that completes the power cycle in one revolution of the crankshaft (two strokes of the piston). A four-stroke engine completes the power cycle in two revolutions of the crankshaft (four strokes of the piston).
Describe the air-cooling system with the help of suitable sketch.
Answer
Air-cooling systems dissipate heat directly from the cylinder walls to the atmosphere. The cylinder block and head are provided with fins to increase the surface area for heat transfer. A fan or the forward motion of the vehicle forces air over these fins, carrying away the heat. This system is simple, lightweight, and typically used in motorcycles and small engines.
Define mean effective pressure and volumetric efficiency of the engine.
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Prove that
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What are the losses in gas turbine combustion chamber?
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Describe the gas turbine cycle with reheating arrangement.
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What are the applications of steam nozzles?
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Write the differences between the water tube and fire tube boilers.
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What is meant by velocity compounding and pressure compounding?
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Derive the expression for condenser vacuum efficiency.
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Part B
Explain the operation of fuel injector with the help of neat sketch.
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Describe the function and working principle of compensating jet arrangement in a carburettor with the help of a diagram.
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Discuss effect of engine variables on the ignition delay in the CI engine.
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What are the types of abnormal combustions? Explain clearly the knocking phenomenon in SI engine.
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What is the function of dynamometer? List the types of dynamometers. Describe the rope brake dynamometer and derive the expression for brake power.
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Describe briefly about the heat balance test.
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During the testing of a 4-stroke oil engine fitted with a simple rope brake dynamometer the following readings were taken. Brake wheel diameter= 60 cm, brake rope dia.= 2.5 cm, dead load on the brake=200 N, spring balance reading= 50 N, speed= 450 rpm, area of the indicator diagram= 4.2 cm2, length of the indicator diagram= 6 cm, spring constant= 6 bar/cm, bore=10 cm, stroke= 15 cm, bsfc=0.3 kg/kWhr, calorific value of the fuel= 43960 kJ/kg. Determine the brake power, indicated power, mechanical efficiency, brake mean effective pressure and indicated thermal efficiency.
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Derive the expression for the work done in a two stage reciprocating air compressor considering the perfect inter cooling.
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Write the differences between reciprocating and rotary air compressors.
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In a gas turbine plant air is compressed from 1 bar and 15°C through a pressure ratio of 6. It is then heated to 727°C in a combustion chamber and expanded back to a pressure of 1 bar. Calculate the work done, work ratio and thermal efficiency when a heat exchanger is fitted. Assume a thermal ratio of 0.75. Take isentropic efficiency of the turbine and compressor as 90% and 85% respectively.
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Explain the operation of Babcock and Wilcox boiler with the help of neat sketch.
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Derive an expression for critical pressure ratio of a convergent-divergent nozzle when steam is expanded isentropically from rest.
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A convergent-divergent nozzle is required to discharge 2 kg of steam per second. The nozzle is supplied with steam at 10 bar and 200°C and discharge takes place against a back pressure of 0.34 bar. Estimate the throat and exit areas. Assume isentropic flow and take n = 1.3. If the nozzle efficiency is assumed to be 85%, determine the exit area.
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At a stage of reaction turbine the mean ring diameter is 140 cm. The speed ratio is 0.7. The speed of rotation is 3000 rpm. Determine the required entrance angle for the blading if the exit angle is 20°. Also calculate the work done per kg of steam flowing per second. Determine the percentage increase in diagram efficiency if the blades are designed for best run at theoretical speed, exit angle being kept 20°.
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Describe the operation of central flow surface condenser with a suitable sketch.
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Write the differences between impulse and reaction turbines.
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