Combustion Chambers Questions and Answers

Answer: A

Correct answer: The whole annulus must be tested

A can chamber can be developed one tube at a time on a modest rig, and the results scale to the full engine. An annular chamber is one continuous flame tube, so a sector test does not reproduce the circumferential flow and the whole annulus must be run at full pressure and temperature. The rig is far larger and each iteration far more expensive, so the programme takes longer.

Answer: B

A sudden reduction takes the mixture below the limit that sustains combustion, so the recirculating products cool below the reignition temperature. Fuel controls schedule deceleration for exactly the same reason they schedule acceleration.

Answer: C

As exit temperatures climb, more air is needed to control the pattern and less can be spared for the walls. Distributing the same protection through many small holes uses less air, which is why effusion has displaced simple slots.

Answer: D

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

Answer: A

Swirling flow sets up a central recirculation carrying hot products back towards the injector to reignite the incoming mixture continuously. It costs pressure loss, and that cost buys the chamber its stability outright.

Answer: B

It compares the peak exit temperature with the mean and the compressor delivery value. A high figure shortens turbine blade life sharply, because the life of a whole row is set by its hottest blade rather than by the average.

Answer: C

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

Answer: D

Thermal formation rises steeply with flame temperature and with the time spent at it. Lean premixed and staged combustors both attack the problem by avoiding those hot regions rather than by treating the exhaust after the fact.

Answer: A

Correct answer: So that its local mixture is near stoichiometric

The overall chamber runs at about 60 to 1 by mass, roughly four times leaner than a flame will sustain. Admitting only a fifth of the air to the primary zone brings the local mixture close to stoichiometric, where the flame is stable and burns quickly. The rest of the air is added downstream, where it completes combustion and then cools the products.

Answer: B

Correct answer: No single condition minimises every regulated emission

The table shows the two families moving in opposite directions with power: nitrogen oxides rise while carbon monoxide and hydrocarbons fall. There is therefore no setting at which all are least, and the certification standard reflects this by measuring emissions over a defined landing and take-off cycle rather than at a single condition.