Question Paper: Thermal Engineering I Question Paper - Jun 15 - Mechanical Engineering (Semester 5) - Jawaharlal Nehru Technological University (JNTUH)

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## Thermal Engineering I - Jun 15

### Mechanical Engineering (Semester 5)

Total marks: 75

Total time: 3 Hours
INSTRUCTIONS

(1) Question 1 is compulsory.

(2) Attempt any **three** from the remaining questions.

(3) Draw neat diagrams wherever necessary.

**1.a.**How the fuel injection system function in CI Engine?

**1.b.**What is the importance of valve and port timing diagrams of I C Engines

**1.c.**What are different power loss resources during combustion of SI Engine?

**1.d.**Explain the importance of heat release rate in the combustion process of CI Engine.

**1.e.**What is the method adopted to measure air fuel ratio of an I C Engine.

**1.f.**Why multi stage compression is required? Explain.

**1.g.**What is dynamic compressors? Explain the significance.

**1.h.**Why the axial compressors are more suitable for gas turbines? Explain.

**1.i.**What is COP of refrigeration system? Explain the importance.

**1.j.**What arc the commonly used refrigerants in vapour compression system?

**PART-B**

**2.a.**Describe the optimum opening position of exhaust vale to reduce the exhaust blow down loss in SI Engine

**2.b.**From the point of view of fuel air cycle analysis how does fuel air ratio effect the efficiency, maximum power, temperature and pressure of the cycle.

OR

**3.a.**Draw the diagram of A/F ratio versus throttle opening for different operating conditions of simple carburetor and explain salient features.

**3.b.**What are the limitations of simple carburetor and how to rectify then? Explain.

**4.a.**Discuss the effect of turbulence and compression ratio on the combustion characteristics in S.I. Engine.

**4.b.**What is the instrument used for the measurement of knocking? Explain the influence of operating parameters on knocking in S.I. Engine.

OR

**5.a.**How to create turbulence in C.I. Engine combustion chamber in order to get better mixing air fuel ? Explain in detail.

**5.b.**What are different additives to be added in C.I. Engine? Explain the use of additives. Describe influence of additives on performance.

**6.a.**A single cylinder, four stroke gas engine has a bore of 180 mm and a stroke of 330 mm and is governed on the hit and miss principle When running at 400 rpm pressure of 6 bar and a pumping loop mean effective pressure of 0.4 bar. Diagram fro the dead cycle give a mean effective pressure of 06 bar When running on no load a mechanical counter recorded 50 firings strokes per minute. Calculate at the full load with regular firing, brake power and the mechanical efficiency of the engine

**6.b.**Differentiate among fans, blowers and compressors.

OR

**7.a.**A six-cylinder four-stroke, direct-injection oil engine is to deliver 120 kW at 1600 rpm.The fuel to be used has a calorific value of 43 MJ/kg and its percentage position by mass is carbon 86%.,hydrogen 13%, and non combustibles 1% .The absolute volumetric efficiency is assumed to 80%, the indicated thermal efficiency 40% and he mechanical efficiency 80%. The air consumption to be 110% in excess of that required for theoretically correct combustion. i) Estimate the volumetric composition of dry exhaust gas, ii) Determine the bore and stroke of the engine, taking a stroke to bore ratio as 1.5 Assume the volume of 1 kg of air at the given conditions as 0.77 $m^{3}$

**7.b.**Explain the working principle of vane type rotary compressor along with a diagram.

**8.a.**20 $m^{3}$ of air per second at 1 bar $15^{\circ} \mathrm{C}$ is to be compressed in a centrifugal compressor through a pressure ratio of 1.5:1 The compression follows the law $\mathrm{PV}^{1 .5}=$ constant The velocity of flow at inlet and out let remains constant and is equal to 60 m/s. If the inlet and outlet impeller diameters are 0.6 m and I.2 m respectively and rotates at a speed of 5000 rpm Find (i) the blade angles at inlet and outlet of the impeller, and the angle at which the air from the impeller enters the casing ; (ii) breadth of impeller blade at inlet and outlet.

**8.b.**Define and discuss the terms power input factor and adiabatic coefficient with a diagram.

OR

**9.a.**Air at 1.01325 bar and 288 K enters an axial flow compressor stage with an axial velocity of 150 ms There are no inlet guide vanes. The rotor stage has tip diameter of 60 cm and a hub diameter of 50 em and rotates at 100 rps.The air enters the rotor and leaves the stator in the axial direction with no change in its velocity or radius.The air is turned through $30.2^{0}$ as it passes through the rotor. Assume a stage pressure of 1.2, calculate power required and degree of reaction.

**9.b.**What is the importance of velocity in angles in power generation?Explain.

**10.a.**Explain the important parameters influence the performance of air refrigeration system.

**10.b.**An ammonia refrigeration plant operates between a condenser temperature of $42^{0} \mathrm{C}$ and an evaporator temperature of $-2^{0} \mathrm{C}$ . The vapour is superheated with a degree of superheat $10^{0} \mathrm{C}$ at the end of compression. The specific heat of ammonia is 2.16 Kj/Kg K. Calculate net refrigeration effect, work required and coefficient of performance.

**11.a.**Differentiate between vapour compression refrigeration system with vapour absorption refrigeration system.

**11.b.**In an open type of refrigeration installation. 1000 kg of atmospheric air are circulated per hour.The air is drawn from the cold chamber at temprature $7^{\circ} \mathrm{C}$ and 1 bar and then compressed isentropic ally to 5 bars. It cooled at this pressure to $27^{\circ} \mathrm{C}$ and then led to the expansion where it expands isentropically down to atmospheric pressure and is discharged to cold chamber .Find the followings.i) Heat extracted from cold chamber per hour .ii) Heat rejected to cooling water per hour .iii) C.O.P of the system . Take for air $\gamma=1.4$ and $C_{p}=1 \mathrm{kJ} / \mathrm{kg} \mathrm{K}$.