Combustion Chambers Questions and Answers

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.

Answer: C

Only two igniters are usually fitted, so the flame must propagate to every other burner through interconnectors or around the annulus. A failure of light-around leaves part of the chamber unlit and produces a badly distorted temperature pattern.

Answer: D

Correct answer: Restart the engine in flight after a flameout

Altitude relight is the ability to relight the main combustor in flight, where the air is thin and cold and the fuel does not vaporise readily. It is a certification requirement, demonstrated over an envelope of altitude and airspeed, and it is one of the constraints that keeps a combustor from being optimised purely for cruise efficiency.

Answer: A

Below a limiting fuel-air ratio the heat released cannot keep the recirculating products hot enough to reignite the incoming mixture. Rapid deceleration is the classic cause, which is why fuel controls schedule the reduction rather than allowing an instant cut.

Answer: B

Almost all of the fuel's chemical energy is released, which is why the parameter matters far more at idle and at altitude relight than at cruise. What separates good chambers from poor ones at cruise is pressure loss and emissions rather than efficiency.