JNTU
JNTU B.Tech III THERMAL ENGINEERING I Previous Question Paper (January/February - 2023 - R16)
Note: i) Question paper consists of Part A, Part B.
ii) Part A is compulsory, which carries 25 marks. In Part A, Answer all questions.
iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions.
PART - A
Point out the Diesel cycle on P-V and T-S planes and mention the four thermodynamic processes involved.
Answer
The Diesel cycle is represented on P-V and T-S planes as a closed loop consisting of four reversible thermodynamic processes:
- Process 1-2: Isentropic compression of air.
- Process 2-3: Constant pressure (isobaric) heat addition.
- Process 3-4: Isentropic expansion of gases.
- Process 4-1: Constant volume (isochoric) heat rejection.
On the P-V diagram, the cycle is bounded by a vertical line (constant volume), a horizontal line (constant pressure), and two adiabatic curves. On the T-S diagram, the cycle is characterized by a vertical line (isentropic), a constant pressure curve, a vertical line (isentropic), and a constant volume curve.
What is a carburettor? State any two functions of carburetor.
Answer
A carburettor is a mechanical device used in spark-ignition engines to prepare the air-fuel mixture by atomizing fuel and mixing it with air in the correct proportions required for various engine operating conditions.
Its two primary functions are:
- Atomization: It breaks the liquid fuel into a fine mist or spray to facilitate rapid evaporation and uniform mixing with the incoming air.
- Metering: It regulates the quantity of fuel supplied to the engine to maintain the appropriate air-fuel ratio (AFR) for different loads and speeds, such as idling, cruising, or acceleration.
Analyse the cause for ignition delay.
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Name important qualities of SI engine fuels.
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What is volumetric efficiency? Name some important variables which affect this efficiency.
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List the advantage of multistage compressor over single stage compressor.
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Indicate the important uses of compressed air for engineering purposes.
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Define pressure coefficient and adiabatic coefficient.
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What are the desired properties of refrigerants?
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Effect of superheating and sub cooling on the CoP of Refrigeration.
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PART - B
Explain the typical valve timing diagram and the significance of each angle in the valve timing diagram of four Stroke Engine.
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What is the significance of chemically correct or stoichiometric air fuel ratio for SI and CI engine?
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Explain in detail about the various stages of combustion in SI engines.
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What are the factors affecting the flame speed of the engine.
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What are the factors to be considered to control the knocking in SI engine? Discuss in detail.
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A 4-cylinder petrol engine has a bore of 60mm and a stroke of 90mm. Its rated speed is 2800 rpm. And it is tested at this speed against brake which has a torque arm of 0.37m. The net brake load is 160N and the fuel consumption is 8.986 lit/hr. The specific gravity of petrol used is 0.74 and it has a lower calorific value of 44100 kJ/kg. A Morse test is carried out and the cylinders are cut out in the order 1,2,3,4 with corresponding brake loads of 110,107,104 and 110 N respectively. Calculate for this speed a) The engine torque b) B.M.E.P c) The brake thermal efficiency d) The specific fuel consumption e) Mechanical efficiency f) I.M.E.P.
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A single acting, two stage reciprocating air compressor with complete inter-cooling delivers 10.5kg per min of air at 16bar. The compressor takes in air at 1bar and 270C. The compression and expansion follow the law pV^1.3 =constant, calculate (a) power required to drive the compressor (b)isothermal efficiency (c) free air delivery (d) Heat transferred in intercooler. If the compressor runs at 440 rpm, the clearance ratios for LP and HP cylinders are 0.04 and 0.06 respectively. Calculate the swept and clearance volumes for each cylinder.
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Explain the construction of centrifugal and axial flow compressors.
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Draw mechanical details of Roots blower and explain the principle of operation.
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In a vapour compression refrigeration system using R-12, the evaporation pressure is 1.4 bar and the condenser pressure is 8 bar. The refrigeration leaves the condenser sub cooled to 300C. The vapour leaving the evaporator is dry and saturated. The amount of heat rejected in the condenser 13.42 MJ/min. Determine (a) refrigeration effect (b) refrigeration load in TR (c) compressor input in kW and (d) COP.
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What is psychrometry? Explain the method to evaluate the psychrometric properties.
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What are the comfortable conditions required for summer? Explain the summer air condition system with schematic and psychometric diagrams.
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