Question

Q2. An ideal turbojet engine consists of a diffuser, compressor, combustor, turbine and a converging nozzle. The engine is operating on an aircraft flying at 250 m/s at an altitude where the air is at 35 kPa and -37 o C. The inlet diameter of this engine is 1.72 m; the thrust produced by the engine under ideal cruising conditions is 60740 N; and the maximum temperature in the jet engine is maintained at 650 o C. Assume constant specific heat values at room temperature, choked flow conditions at nozzle exit and ideal operation for all components of the engine. The jet fuel has a heating value of 42,700 kJ/kg.

The minimum fuel consumption rate required (kg/s) under the cruising conditions given in the problem is:

Answer 1

GIVEN:

calorific value of fuel = 42700 kJ/Kg

speed of the aircraft = 250 m/s

thrust produced (ideal cruising) = 60740 N

for minimum fuel consumption rate under cruising condition:

for ideal turbojet, all fuel burnt, will be used to produce the thrust.

[mass flow rate of fuel * calorific value of fuel ] = [ thrust produced * speed of the aircraft ]

_f * (42700 * 1000) = ( 60740 * 250 )

_f = 15185000 / 42700000

_f = 0.356 Kg/sec