Combustion Chambers Questions and Answers

Answer: C

Correct answer: Only three

The first three pair each feature with its purpose. The fourth reverses the swirler’s effect: swirl adds pressure loss rather than reducing it, and it is accepted precisely because there is no other way to anchor a flame at combustor velocities. The trade of a little total pressure for a stable flame is one the designer makes deliberately.

Answer: D

Correct answer: Only three

The first three pair each parameter with what it measures. The fourth repeats combustion efficiency’s definition under the name of pattern factor, which measures something quite different - the non-uniformity of the exit temperature, and hence how much hotter the worst blade runs than the average.

Answer: A

Correct answer: Diffusion zone

The three zones of the flame tube are primary, intermediate and dilution. The diffuser is a separate component upstream, between the compressor and the flame tube, whose job is to slow the air before it enters. It is not a zone of the flame tube, though the similarity of the words makes it a plausible distractor.

Answer: B

Correct answer: Nitrogen oxides

Nitrogen oxide formation depends exponentially on flame temperature, so it is at its lowest at idle and its highest at take-off - the opposite of the other three. Carbon monoxide, unburnt hydrocarbons and combustion inefficiency all peak at idle, where the chamber runs cool and the reactions do not go to completion.

Answer: C

The other three all reduce the local velocity or return hot products to the incoming mixture. Raising the delivery velocity does the opposite and would blow the flame downstream, which is precisely what the diffuser exists to prevent.

Answer: D

Correct answer: They are the easiest arrangement to develop and test

This is the annular chamber’s weakness rather than its strength. Its single continuous flame tube cannot be tested a sector at a time, so the whole annulus must be run on an expensive rig. The other three are genuine advantages, and together they are why annular chambers dominate modern engines despite the development cost.

Answer: A

Correct answer: Increasing residence time in the primary zone

Nitrogen oxide formation is slow relative to the combustion itself, so the quantity produced grows with the time the gas spends at high temperature. Lengthening the residence time therefore increases it. The other three all reduce it, and all three work the same way - by holding the peak flame temperature down, which is the variable the exponential depends on.

Answer: B

Reaction rates fall steeply with pressure, so a spark that lights the chamber easily on the ground may not do so at altitude. The relight envelope is published as a band of altitude and airspeed precisely because success depends on both.

Answer: C

The mean exit temperature can be entirely acceptable while a circumferential hot streak destroys the blades it passes over. Repositioning the dilution holes is the usual remedy, and the traverse must be re-measured to confirm it worked.

Answer: D

Reaction rates fall sharply with the cooler, lower pressure conditions of idle, so carbon monoxide and hydrocarbons survive to the exhaust. Nitrogen oxides behave oppositely, which is why the certification cycle weights several power settings.