Combustion Chambers Questions and Answers

Answer: C

Every gain in weight, length and exit pattern uniformity costs more in rig testing and instrumentation. A can could be run individually, whereas an annulus must be tested whole, which is a large and unavoidable expense.

Answer: D

Reaction rates fall steeply with pressure, so a spark that lights the chamber easily on the ground may fail entirely at altitude. The relight envelope is published as a band of altitude and airspeed for exactly this reason.

Answer: A

Correct answer: Combustion efficiency

Every serious design exceeds 99 per cent at cruise, so the spread between a good chamber and a poor one is a fraction of a per cent and tells you almost nothing. The other three vary widely and matter directly: pressure loss costs thrust, pattern factor sets turbine blade life, and the air split follows from the overall ratio.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the necessity. At about 60 to 1 overall the chamber is far too lean to burn - roughly four times leaner than the weak limit. Dividing the air lets the primary zone run near stoichiometric while the remainder is added downstream to complete combustion and then to cool the products before the turbine.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason is the purpose. Compressor delivery velocity is of the order of 150 m/s, far above any flame speed, so a flame could not be held in it. The diffuser slows the air to something the swirler and recirculation zone can work with, and it must do so without separating, which is why its design is a problem in its own right.

Answer: D

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the justification. Turbine blade life depends on the temperature the hottest blade actually sees, and creep life falls very steeply with temperature, so a hot streak in the exit traverse costs far more life than a uniformly higher average would. Pattern factor quantifies that non-uniformity, and reducing it is worth as much development effort as efficiency.

Answer: A

Both statements are true and the second is the reason. A pilot stage optimised for stability handles idle and a main stage optimised for low nitrogen oxides takes over at power, so neither has to compromise for the other.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason is the hazard being guarded against. The airflow falls with shaft speed and therefore lags a rapid fuel reduction, so cutting fuel too fast leaves the primary zone below the weak extinction limit and the flame goes out. The deceleration schedule sets a minimum fuel flow that keeps the mixture inside the limit at every speed.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the pressure. As turbine entry temperatures have risen, more of the compressor delivery air is needed for combustion and dilution, leaving less for the walls. Effusion cooling, using many small angled holes to build a continuous film, protects the wall with substantially less air than the older discrete slots, which is why it has displaced them.

Answer: D

The reason is true but the assertion is false. Development requires testing the whole annulus rather than rigging a single can, which is precisely the expense that kept can and cannular chambers in service for so long.