Combustion Chambers Questions and Answers

Answer: A

The Brayton cycle idealises combustion as constant pressure, and a real chamber loses perhaps three to six per cent of the total pressure through it. That loss matters because every one per cent costs rather more than one per cent of the engine's thrust.

Answer: B

Compressor delivery velocities of well over a hundred metres per second would blow any flame downstream immediately. The diffuser and snout slow the air first, and swirl and recirculation then anchor the flame in a region of much lower velocity.

Answer: C

Only near stoichiometric does the flame burn fast enough and hot enough to be self sustaining. The overall chamber is far leaner than this, which is why the air is deliberately divided between zones rather than admitted all at once.

Answer: D

Combustion products leave the primary zone far hotter than any turbine blade could survive, so the remaining air is admitted through dilution holes. Placing those holes correctly also governs the temperature pattern the turbine actually sees.

Answer: A

Swirling flow sets up a central recirculation that carries hot products back towards the injector and continuously reignites the incoming mixture. Without that recirculation the flame would simply be swept downstream and blown out.

Answer: B

Stoichiometric for kerosene is close to 15 to 1, so the overall chamber runs roughly four times leaner. Only the primary zone burns near stoichiometric, and the remaining air cools the walls and dilutes the products afterwards.

Answer: C

A thin layer of relatively cool air is introduced through rows of slots and hugs the wall, keeping the flame off the metal. Effusion cooling achieves the same end through many small holes and uses less air, which matters as turbine entry temperatures rise.

Answer: D

Each can is a self contained chamber that can be removed and tested individually, which made development straightforward on early engines. The arrangement is heavy and bulky, which is why modern engines use annular chambers instead.

Answer: A

Correct answer: Several flame tubes within one annular casing

The cannular or tubo-annular arrangement is the compromise between the two extremes. It keeps the separate flame tubes of the can design, so each can be developed and tested on its own, while enclosing them in a single annular casing, which saves the length and weight of separate casings. Interconnectors between the tubes allow the flame to spread at light-up.

Answer: B

It gives the shortest and lightest chamber for a given output and the most uniform exit temperature. The difficulty is that development requires testing the whole annulus, which is expensive compared with rigging a single can.