Gas Dynamics and Jet Propulsion – Unit 4

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Gas Dynamics and Jet Propulsion – Unit 4

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Gas Dynamics and Jet Propulsion – Unit 3

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Gas Dynamics and Jet Propulsion – Unit 4

Problem: The flight speed of a turbojet is 600 kmph at 10000 m altitude. The density of air at that altitude is 0.17 kg/m3.. The drag for the plane is 6.8 kN. The propulsive efficiency of the jet is 60%. Calculate the specific fuel consumption (SFC), air-fuel ratio (AF), and jet velocity (cj). Assume calorific value of the fuel as 45 MJ/kg and overall efficiency of the turbo jet as 18%.

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Gas Dynamics and Jet Propulsion – Unit 4

Problem: The diameter of the propeller of an aircraft is 2.5 m. It flies at a speed of 500 kmph at an altitude of 8000 m. For a flight to jet speed ratio of 0.75, determine (a) mass flow rate through the propeller, (b) thrust produced, (c ) specific thrust, (d) specific impulse, and (e) thrust power.

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Gas Dynamics and Jet Propulsion – Unit 4 Problem: A turbo jet propels an aircraft at a speed of 900 kmph while taking 3000 kg of air per minute. The isentropic enthalpy drop in the nozzle is 200 kJ/kg and nozzle efficiency is 90%. The air fuel ratio is 85 and the combustion efficiency is 95%. The calorific value of the fuel is 42 MJ/kg. Calculate (a) thrust power, (b) power output of the engine, (c ) thermal efficiency, (d) propulsive efficiency, (e) Specific Thrust and (f) Specific Impulse.

Continued..

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Gas Dynamics and Jet Propulsion – Unit 4

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Gas Dynamics and Jet Propulsion – Unit 4 Problem: A turbo jet aircraft flies with a velocity of 300 m/s at an altitude where air pressure is 0.35 bar and temperature – 400C. The compressor has a pressure ratio of 10 and temperature of gases at the turbine inlet is 1100 0C. Air enters the compressor at the rate of 50 kg/s. Estimate (a) the temperature and pressure of gases at turbine exit, (b) temperature and Velocity of gases at the nozzle exit, (c ) Flight to Jet speed Ratio and (d) propulsive efficiency of the cycle.

M M* T//T0 p/p0 A/A* F/F*

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Gas Dynamics and Jet Propulsion – Unit 4

Problem: A jet propelled plane has 2 jets, 250 mm diameter and net power at turbine is 3 MW. Fuel consumption per kWhr is 0.42 kg with CV = 49 MJ/kg. When flying at a speed of 300 m/s in an atmosphere having density of 0.168 kg/m3. the air fuel ratio is 53. Calculate (a) absolute velocity of jet, (b) resistance of the plane, (c ) Thrust Power, (d) Engine Power Output, and (e) Propulsive Efficiency, overall efficiency and thermal efficiency.

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1. Draw the h-s diagram for diffuser process. 2. Write the equation for diffuser efficiency for small pressure rise and large

pressure rise in a diffuser. 3. Write the equation for isentropic compression in a compressor. 4. Draw the h-s diagram for compression process in a compressor. 5. Write the equation for compressor efficiency of the compressor. 6. Draw the h-s diagram for combustion process in a combustion chamber. 7. Write the equation for heat transferred per kg of gases in a combustion

chamber. 8. Write the equation for combustion efficiency of the combustion chamber. 9. Draw the h-s diagram for turbine process. 10. Write the equation for isentropic efficiency of a turbine. 11. Draw the h-s diagram for nozzle process. 12. Write the equation for nozzle efficiency. 13. Write the equation for exit velocity of gases in a nozzle.

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14. Write the relation for thrust force considering the mass flow rate of fuel. 15. Write the relation for thrust force neglecting the mass flow rate of fuel. 16. Write the equation for thrust power or propulsive power of a turbo jet. 17. Write the equation for power output of engine PE. 18. Write the equation for propulsive efficiency of a turbo jet. 19. Write the equation for propulsive efficiency in terms of flight to jet speed

ratio. 20. What is the condition for maximum thrust power?

21. What is the propulsive efficiency for maximum thrust condition?

22. Write the relations for mechanical efficiency, combustion efficiency and thermal efficiency.

23. Write the relation for overall efficiency? Express the relation also in terms of mechanical efficiency, combustion efficiency and thermal efficiency.

24. Define TSFC. 25. Define specific thrust and specific impulse. 26. Define effective jet velocity.

END OF UNIT 4

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