Combustion Chamber in Turbine Engines

Purpose and Design

Combustion Chamber Role
- Contains burning air-fuel mixture from the compressor and fuel spray nozzles.
- Generates maximum heat release at constant pressure for turbine efficiency.
Challenges
- Designing for efficient fuel use and reducing atmospheric pollution.
- Limiting gas temperature to prevent turbine blade distortion and failure.

Material Temperature Limits
- Nozzle guide vanes and turbine blades can withstand up to 1700°C.
Air Temperature Increase
- Air from the high-pressure compressor may be at ~550°C.
- Fuel addition raises gas temperature by ~1150°C.
Variable Power Settings
- Full power reaches 1700°C; lower settings mean lower temperatures.

Airflow Dynamics
- Air slows and pressure increases after leaving the compressor through a divergent duct.
- Slowing air is crucial to maintain flame; kerosene flame rate is ~30 feet/second.
Air Division
- Air is divided into primary, secondary, and tertiary flows.
Primary Air
- About 20% of total airflow; mixed in a 15:1 weight ratio with fuel.
- Slowed by flare and swirl vanes to maintain flame stability.
Secondary Air
- Another 20% of airflow; stabilizes flame and forms a toroidal vortex.
Tertiary Air
- Remaining 60% gradually introduced; cools casing and exits gases.

Flame Tube Cooling
- Ceramic-coated tiles with ridged surfaces enhance heat transfer.
- Transpiration cooling method forms insulating air film.

Ignition and Flame Propagation
- Typically two igniters; interconnector spreads the flame between chambers.
Pressure Equalization
- Combustion pressure equalizes across chambers, stopping inter-chamber gas flow.

Expansion and Sealing
- Sealing ring accommodates chamber expansion into the nozzle box.

Development
- Originated from Sir Frank Whittle's design.
- Used in axial flow and centrifugal compressor engines.
Current Use
- Still in use in engines like the Rolls-Royce Dart.

Wet Start Prevention
- Drain tubes remove excess fuel to prevent dangerous torching during start attempts.