the workings of the combustion chamber
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DESCRIPTIONJet Combustion Chamber
The Workings of the Combustion Chamber
The Workings of the Combustion ChamberKelvin Tam
1IntroductionEssentially acts as the heart of the engine: converts chemical energy into mechanical energy Important to optimize performance because air stream has sustained a number of pressure losses by the time it reaches the inlet of the chamberGoal of all components prior to the combustion chamber is to slow air down to almost stagnation to facilitate mixing between air and fuel
2At a Glance: A Single Cell of the Chamber
Primary Stream: Near stagnant air that enters the dome and combustor via liner holes, and is eventually mixed with fuel and combusted.
Intermediate Air: Diluting high concentrations of carbon monoxide and hydrogen that may create hot spots when burnedand also cools the air.
Dilution Air: Enters the liner towards the end of the chamber and are used to cool the air and generate a uniform temperature gradient before entering the turbine blades 4The LinerConstructed with high heat resistant superalloys (Ni, Fe, Co based) and protected with thermal barrier coatingFilm cooling: Cool air is injected into just inside the liner to cool the metal via convection from around 1800K to roughly 800KTranspiration cooling,: Uses a porous material that allows for cooling air to pass through which results in much more uniform temperature profile.This method uses roughly 10% of total airflow while film cooling uses anywhere from 20 to 50%.
5Case sees mainly pressure loads (low maintenance)Majority of the thermal loads generated by combustion is seen by the liner which also introduces the separate air streams together Dome and SwirlerResponsible for mixing air with fuel to facilitate combustion by generating vortices that induce turbulent flowEarly designs use a simple flat plate in a bluff body dome design that generates wake turbulence Newer designs use swirlers that create a low pressure environment for the flows to recirculate after combustionGives greater control over degree of turbulence, since turbulent flow creates pressure losses
6 primary air flow that is separated from the rest of the flow using the snoutmuch like the vortices seen around wingtips) Types of Combustion Chambers
Combustors arranged axisymmetrically and each has its own set of components. Waste products enter shared exhaust
Easy to service individual combustors
Drawback: Redundant parts add weight
Types of Combustion ChambersEach liner has its own fuel injector and combustion zone, but the pressures in each liner is reduced by a series of liner holes and combustion tubes that allow hot gases to mix across liners.
Drawback:servicing and testing becomes more cumbersome than the can design.
8This results in a more uniform temperature distribution and eliminates the need for multiple igniters.
Types of Combustion Chambers
Single continuous liner inside an annular casing.
Reductions can also be made in length which leads to a lighter, shorter engine
Double annular combustor: Pilot zone, operates at low power settings. If additional power is needed the main zone is turned on as well.
9Because combustion occurs across a single liner as opposed to separate chambers, combustion is the most uniform
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