Homework Help: Engine cycle analysis pls help

1. Nov 14, 2008

claire_hender

A twin- spool turbojet powered aircraft flies at 600(ms-1) at an altitude where the temperature and pressure are 0.116bar and 216K. The air mass flow rate into the engine intake is 20kgs-1. The isentropic efficiences of the components are: intake (diffuser) 0.95; low pressure compressor: 0.92, high pressure compressor: 0.94. High pressure turbine: 0.96, low pressure turbine: 0.97; nozzle 0.98. There is power take-off from the low pressure spool of 250kW and 0.5kgs-1 of air is bled from the low pressure compressor. Compressor pressure ratios are 1.5 and 2 for the low and high pressure compressors respectively, and the combustion chamber operates a constant pressure. The combustion chamber exit temperature is 850 degreesC, and the nozzle expands the gas to the ambient pressure.

The question is: Perform a complete engine cycle analysis to determine the nozzle exhaust velocity and hence the engine thrust.

I know the mass flow rate if the high pressure compressor = 19.5 kgs-1
And similarly through the high pressure turbine = 19.5 kgs-1
Also, my intake (diffuser) pressure ratio = p2/p1 = 7.614

Apart from that I am really stuck, I don't know how to actually start the question? If anyone could give me any guidelines or help, it'd be much appreciated.
Thank you !! xxx

2. Dec 23, 2008

deepthishan

i find that the best way to tackle these questions is to start with a schematic diagram of the twin spool engine then construct a t-s sketch.
im not about to do all that here! but anyway it's not as hard as it sounds. use the efficiency equations for the compressors, turbines and nozzles, dont forget to use the combustor pressure loss fact and the mechanical efficiency of each spool as well.
go step by step very gradually and ul end up with the answer
gluck