Menoufia University 4th year
Faculty of Engineering Design of Steam and Gas Turbines (MPE 424 B)
Department of Mech. Power Eng. Sheet (6) Jet-Propulsion Cycles
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1) The following data apply to a turbojet unit of Boeing aircraft flying at altitude of 6.1 km
while the ambient conditions are 246 K and 0.458 bar.
Speed of the aircraft 805 km/hr
Pressure ratio of compressor 4:1
Combustion chamber pressure loss 0.21 bar
Turbine inlet temperature 1100 K
Intake duct efficiency 95%
Isentropic efficiency of compressor 85%
Isentropic efficiency of turbine 90%
Mechanical efficiency of transmission 99%
Nozzle efficiency 95%
Nozzle inlet area 0.0935 m2
L.C.V of fuel 45000 kJ/kg
Find the thrust and specific fuel consumption in kg/hr. N of thrust. Assume convergent
nozzle.
2) A turbo-prop aircraft is flying at 600 km/h at an altitude where the ambient conditions are
0,458 bar and -15oC. compressor pressure ratio 9:1. maximum gas temperature 1200 K. the
intake duct efficiency is 0.9 and total head isentropic efficiency of compressor and turbine is
0.89 and 0.93 respectively. Calculate the specific output in kW/kg of air/sec and thermal
efficiency of the unit taking mechanical efficiency of transmission as 98% and neglecting the
losses other than specified. Assume that exhaust gases leave the aircraft at 600 km/h relative
to the aircraft.
Hint : No thrust as the unit is turboprop.
3) A turbojet aircraft is flying with a velocity of 320 m/s at an altitude of 9150 m, where the
ambient conditions are 32 kPa and -32°C. The pressure ratio across the compressor is 12, and
the temperature at the turbine inlet is 1400 K. Air enters the compressor at a rate of 60 kg/s,
and the jet fuel has a heating value of 42,700 kJ/kg. Assuming ideal operation for all
components and constant specific heats for air at room temperature, determine (a) the velocity
of the exhaust gases, (b) the propulsive power developed, (c) the rate of fuel consumption, (d)
the propulsive efficiency, (e) the thermal Efficiency., and (f) the overall Efficiency.
4) Repeat Problem 3 using a compressor efficiency of 80 percent and a turbine efficiency of 85
percent.
5) Consider an aircraft powered by a turbojet engine that has a pressure ratio of 12. The aircraft
is stationary on the ground, held in position by its brakes. The ambient air is at 27°C and 95
kPa and enters the engine at a rate of 10 kg/s. The jet fuel has a heating value of 42,700 kJ/kg,
and it is burned completely at a rate of 0.2 kg/s. Neglecting the effect of the diffuser and
disregarding the slight increase in mass at the engine exit as well as the inefficiencies of engine
components, determine the force that must be applied on the brakes to hold the plane stationary.
Answer: 9089 N
1
6) Air at 7 °C enters a turbojet engine at a rate of 16 kg/s and at a velocity of 300 m/s (relative
to the engine). Air is heated in the combustion chamber at a rate of 15,000 kJ/s and it leaves
the engine at 427°C. Determine the thrust produced by this turbojet engine. (Hint: Choose the
entire engine as your control volume.).
7) Air at 22 kPa, 220 K, and 250 m/s enters a turbojet engine in flight at an altitude of 10,000
m. The pressure ratio across the compressor is 12. The turbine inlet temperature is 1400 K, and
the pressure at the nozzle exit is 22 kPa. The diffuser and nozzle processes are isentropic, the
compressor and turbine have isentropic efficiencies of 85 and 88%, respectively, and there is
no pressure drop for flow through the combustor. On the basis of an air-standard analysis,
determine:
(a) the pressures and temperatures at each principal state, in kPa and K, respectively.
(b) the velocity at the nozzle exit, in m/s.
(c) Propulsive efficiency.
Neglect kinetic energy except at the diffuser inlet and the nozzle exit.
8) For the turbojet in Problem 7, plot the velocity at the nozzle exit, in m/s, the pressure at the
turbine exit, in kPa, and the rate of heat input to the combustor, in kW, each as a function of
compressor pressure ratio in the range of 6 to 14. Repeat for turbine inlet temperatures of 1200
K and 1000 K.
9) Consider the addition of an afterburner to the turbojet in Problem 7 that raises the
temperature at the inlet of the nozzle to 1300 K. Determine the velocity at the nozzle exit, in
m/s.
10) Air enters the diffuser of a ramjet engine at 40 kPa, 240 K, with a velocity of 2500 km/h
and decelerates to negligible velocity. On the basis of an air-standard analysis, the heat addition
is 1080 kJ per kg of air passing through the engine. Air exits the nozzle at 40 kPa. Determine
(a) the pressure at the diffuser exit, in kPa.
(b) the velocity at the nozzle exit, in m/s.
Neglect kinetic energy except at the diffuser inlet and the nozzle exit.
11) A turboprop engine consists of a diffuser, compressor, combustor, turbine, and nozzle. The
turbine drives a propeller as well as the compressor. Air enters the diffuser with a volumetric
flow rate of 83.7 m3/s at 40 kPa, 240 K, and a velocity of 180 m/s, and decelerates essentially
to zero velocity. The compressor pressure ratio is 10 and the compressor has an isentropic
efficiency of 85%. The turbine inlet temperature is 1140 K, and its isentropic efficiency is 85%.
The turbine exit pressure is 50 kPa. Flow through the diffuser and nozzle is isentropic. Using
an air-standard analysis, determine
(a) the power delivered to the propeller, in MW.
(b) the velocity at the nozzle exit, in m/s.
Neglect kinetic energy except at the diffuser inlet and the nozzle exit.
