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Flame & Combustion

Prabir Basu

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WHAT IS A FLAME

Flame is a zone of intense chemical

reaction with liberation of heat and light

What is combustionCombustion is a exothermic oxidation

of a fuel at high temperature.

C + O2 = CO2 - Q

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Flame types

Diffusion flame Premixed flame

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Flame velocity

Flame travels at a specific speed against the unburnt mixture. This

speed is equal to the local mixture velocity for a stable velocity, andit depends on;

1. Fuel: air mixture ratio (increases and decreases)

2. Preheat temperature of the mixture (increases )

3. Turbulence intensity in the flow field (increases )

This velocity is also called

burning velocity. This velocityis equal to the local velocity of

the unburnt gas normal to the

flame front.

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Flame velocity

Equivalence ratio

Flammability limits

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200

400

600

800

1000

1200

Temperature

(C)

0 3 15 200Time (s)

Drying

and

Heating

Volatile

ReleaseIgnition Secondary

fragmentation

Attrition

fines

Primary

fragments

dv = 3 mm

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Coal Combustion

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Mass Tran

Reaction

Reaction

Mass Transfer

Mass Transfer