Combustion and Turbines
Combustion and Turbines covers the hot section: how fuel is mixed and burned, how the flame is stabilised, and how turbine stages extract work without exceeding metal limits.
Combustor and turbine rules
- Combustor types include annular, can-annular and reverse-flow; all use a primary zone, intermediate zone and dilution or cooling air.
- Fuel nozzles atomise fuel; poor atomisation causes hot streaks, carbon and high TGT spread.
- The combustor pressure drop drives air through the liner and cools the walls.
- Nozzle guide vanes accelerate and turn hot gas; turbine blades extract work by impulse and reaction.
- Cooled blades and vanes use compressor air; blockage or excess cooling air affects both life and efficiency.
- TGT probes measure gas temperature near the turbine inlet; EGT is measured further downstream. They are not interchangeable limits.
Worked example
A turbine stage passes 5.0 kg/s of gas with specific heat about 1.15 kJ/kg·K and a temperature drop of 250 K. Power = mass flow × specific heat × temperature drop = 5.0 × 1.15 × 250 = 1437.5 kW, or about 1.44 MW. If stage efficiency is 0.88, shaft-equivalent work is about 1.26 MW. The calculation shows why a small TGT increase represents a large power change, and why over-temperature is limited by blade creep and oxidation.
Traps
- Treating TGT and EGT as the same reading.
- Assuming cooling air is free; it costs compressor work.
- Ignoring TGT spread between probes.
- Diagnosing a hot section solely from colour.
- Mismatching fuel nozzles or failing to check spray pattern.