Combustion Chambers Questions and Answers

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.

Answer: C

It compares the peak exit temperature with the mean and the compressor delivery temperature, and a high value shortens turbine blade life sharply. Dilution hole placement is the main tool for controlling it in a given chamber.

Answer: D

Thermal formation rises steeply with flame temperature and with residence time, so the near stoichiometric primary zone dominates. Lean premixed and staged combustors both attack the problem by avoiding those hot regions in the first place.

Answer: A

Low pressure and temperature at idle slow the reactions and leave the oxidation incomplete. Nitrogen oxides behave in exactly the opposite way, which is why no single operating condition minimises every regulated emission at once.

Answer: B

Rich pockets near the injector pyrolyse fuel into soot before enough air reaches them. Improved atomisation and better primary zone mixing both reduce it, which is why modern injectors are designed around the fuel spray as much as the airflow.

Answer: C

A pilot stage optimised for stability handles idle, and a main stage optimised for low nitrogen oxides takes over at high power. Splitting the duty this way lets each stage be designed for one condition rather than compromising across the whole range.

Answer: D

Total pressure lost in the chamber is pressure the turbine and nozzle never see. Some loss is unavoidable because the dilution jets must penetrate the flow, so the design balances mixing quality against the pressure it costs to achieve it.