College of Engineering

Mechanical and Aerospace Engineering Department

Dr. Daniel R. Kirk

Professor

Associate Dean

November 27, 2017

Written Exit Exam Questions for Adam Truszkowski

Mechanical and Aerospace Engineering Department

Florida Institute of Technology

Ehsan,

The following problems ask you to apply your knowledge of combustion to two propulsion applications. What I am most interested in evaluating is your ability to formulate a coherent and thought-out engineering approach toward arriving at a solution. In both problems, explicitly state any assumptions you use in solving these problems. Also site any sources that you use in solving these problems. The questions are open book, open notes, and you may use any online and library resources that help you solve the problems. Spend no more than 48 hours on the exam.

If you have any questions, please feel free to email.

Best wishes on your comprehensive exams,

Regards,

Dan

Problem 1: Combustion related to Air-Breathing Propulsion

A jet engine gas turbine combustor is designed for very fast mixing. The combustor volume is 0.02 m3, and the conditions at the inlet are 610 K and 25 atmospheres. Assume that the fuel is benzene, C6H6, and the equivalence ratio is 0.5. The overall reaction rate is given by Equation 1:

/ Eq.1

The units in the equation are mol, s, m, and K.

Answer the following questions, making any additional reasonable and justifiable assumptions that you need:

1)Evaluate the maximum power this combustor can generate.

2)Evaluate the combustion efficiency at this maximum power.

3)How does the maximum power change as the altitude changes, noting that both the pressure and temperature drop as the airplane climbs upward?

4)Without adjustment, this engine will eventually quit at a certain altitude, why? What sort of maneuver can be used to relight?

5)Model the combustor as a single square cylinder (cylinder length is equal to the diameter) made of titanium with a wall thickness of 5 mm.

  1. What is the instantaneous heat flux to the wall assuming that combustion products within the combustor (within the cylindrical volume) are all at constant temperature? Assume that external to the combustor the air temperature in the rest of the engine is a uniform 500 K.
  2. At steady-state, what is the temperature distribution through the combustor wall?
  3. At steady-state operation (as compared with room temperature of 300 K), how much does the combustor itself expand and what are the stresses in the wall?

Problem 2: Combustion related to Rocket Propulsion

An arc-jet propulsion system heats H2 to 5,000 K at 1 atmosphere pressure. It then expands in a nozzle to vacuum. Assuming equilibrium in the chamber (upstream of the C-D nozzle), estimate the exhaust velocity for the two bounding cases:

1)Frozen flow

2)Equilibrium