Combustion Section (combustion process, chamber types, fuel nozzles)
What this domain tests
The combustion section domain tests the chain from diffuser to turbine inlet: how fuel is atomized and mixed, how the flame is stabilized, why the liner has primary, intermediate, and dilution zones, and how chamber type affects maintenance and emissions.
Core rules
- The diffuser slows air and raises static pressure before the liner; the pressure loss is a deliberate trade for flame stability.
- Can, can-annular, and annular chambers differ in packaging and maintenance. Annular chambers are shorter and give more uniform exit temperature.
- Fuel nozzles may be simplex, duplex, or airblast. Atomization quality controls local fuel-air ratio, smoke, and liner life.
- The primary zone runs near stoichiometric for stability; dilution air cools the gas before the turbine. Rich blowout, lean blowout, and autoignition bound the operating envelope.
Worked example
Estimate combustor temperature rise for a fuel-air ratio f = 0.020 and lower heating value 43,000 kJ/kg. With cp about 1.15 kJ/(kg.K): delta T is about f x LHV / [(1 + f)cp] = 0.020 x 43,000 / (1.020 x 1.15) = 733 K. If inlet air is 800 K, exit is about 1,533 K. The reasoning shows why turbine cooling and dilution air are needed: metal limits are far below this gas temperature.
Traps
Assuming the combustor raises pressure; confusing primary and dilution air; treating all fuel nozzles as interchangeable; ignoring the pressure-loss penalty; forgetting that too lean a mixture causes lean blowout.