The Workings of the Combustion Chamber

Kelvin Tam

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Introduction

Essentially 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 chamber

Goal of all components prior to the combustion chamber is to slow air down to almost stagnation to facilitate mixing between air and fuel

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At a Glance: A Single Cell of the Chamber

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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 4

The Liner

Constructed with high heat resistant superalloys (Ni, Fe, Co based) and protected with thermal barrier coating

Film cooling: Cool air is injected into just inside the liner to cool the metal via convection from around 1800K to roughly 800K

Transpiration 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%.

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Dome and Swirler

Responsible for mixing air with fuel to facilitate combustion by generating vortices that induce turbulent flow

Early 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 combustion

Gives greater control over degree of turbulence, since turbulent flow creates pressure losses

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Types of Combustion ChambersCombustors 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

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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. 8

Types of Combustion ChambersSingle 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.

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Reducing Fuel Emissions: Boeing PhantomEye

Boeing PhantomEye drone uses hydrogen fuel, which has a much higher energy density than comparable fossil fuel and has shown it can climb to heights of 65000 ft in 2012.

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Reducing Fuel EmissionsIn the same year, a United Airlines aircraft 737 made a commercial flight on a hybrid fuel made of jet fuel and a biofuel called Solajet, which is produced by feeding sugars to a genetically modified algae.

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Questions?

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ReferencesWikipedia, Combustor:

https://en.wikipedia.org/wiki/Combustor

Popular Science,10 OF THE GREATEST AEROSPACE INNOVATIONS OF 2012http://www.popsci.com/technology/article/2012-11/best-whats-new-aerospace-2012?image=5

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