# Steady Flow Energy Equation Problem.

1. Aug 15, 2010

### djw42

I have been trying for literally days on this problem and its completley done me in.

The problem is as follows.

I have to evaluate a jet engine using the SFEE equation.

So far I have concluded that this equation will be the best to use...

Qr – Wrx = ṁ Δ [ h + ½ Ṽ2].

Although my problem is I only have the following data available to me...

"h0e/he ratio of total-to-static enthalpy at exit from the engine
h1 J/kg enthalpy at entry to the engine
Ṽ1 m/s airspeed at entry to the engine
ṁ engine air mass flow rate, kg/s
κ fraction of fuel energy input lost to the atmosphere
Pe static pressure the engine exit, kPa
You should assume Cp/R for the exhaust gases to be 4.33, and take the calorific value of the fuel to be 43 MJ/kg."

and I cannot work out for the life of me how to do it.

I really hope someone on here can help.

Thanks..

Daniel.

2. Aug 15, 2010

### dtango

Is this for a ramjet, turbojet, or turbofan? Regardless an approach to this is to assume an ideal jet (ram, turbo, or turbofan) and then apply Brayton's Cycle for the various stages in the engine for Brayton's cycle.

The knowns are giving you pieces of information for each stage of the cycle. Temperature, pressure, and mach number relationships exist for each stage that estimate the performance of the jet. It's a matter of figuring out out how the enthalpy and other known's relate to those temperature, pressure, and velocity relationships for the various stages of the cycle. Work the problem a stage at a time.

Here are two resources from MIT you might consider studying to help you:
http://web.mit.edu/16.unified/www/SPRING/propulsion/notes/node18.html
http://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node85.html

Last edited by a moderator: Apr 25, 2017
3. Aug 15, 2010

### djw42

That would be great although I cant assume its ideal as a later question is to compare this engine to an ideal engine.

As for the engine type I have no idea as the question does not state.

As for braytons cycle, i have never heard of it which means it would unlikley be about that although I will look into it.

Thanks for the help, out of the several forums iv posted this question on this is the only one where someone hasnt given me an arrogant, "get off my forum" reply.