Experiments on Strained Premixed Flames in the Distributed Reaction Regime

rangebeaverMechanics

Feb 22, 2014 (3 years and 3 months ago)

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Experiments on Strained Premixed Flames in the Distributed Reaction Regime

Alessandro Gomez, Department of Mechanical Engineering, Yale University, USA

In

turbulent

premixed

combustion,

experimental

investigation

of

the

non
-
flamelet

regime

still

remains

an

open

challenge
.

The

non
-
flamelet

regime

corresponds

to

a

situation

of

discontinuous

flame

sheets

locally

extinguished

by

turbulent

eddies

and

is

expected

in

very

intense

turbulence,

at

turbulent

Karlovitz

number

greater

than

100
.

Conditions

of

strong

turbulence

and

chemistry

interaction

are

particularly

hard

to

reproduce

in

a

laboratory
-
scale

burner

and

rare

evidence

of

the

non
-
flamelet

regime

under

such

conditions

has

been

reported

to

date
.

In

this

project,

we

demonstrated

how

highly

turbulent

flames

with

real

flame

effects,

such

as

heat

losses

and

combustion

product

stratification,

can

be

established

in

a

compact,

bench
-
top

experiment,

that

is

amenable

to

computational

modeling

and

even

direct

numerical

simulation
.

The

configuration

shows

a

rich

phenomenology,

including

local

extinction

and

reignition,

as

evidenced

by

OH

fluorescence
.

The

so
-
called

extended

Borghi

diagram

is

used

to

identify

various

turbulent

combustion

regimes,

with

turbulent

velocity

and

integral

length

scales

normalized

with

respect

to

the

laminar

flame

speed

and

the

flame

thickness
.

The

extended

Borghi

diagram

is

an

idealization
.

The

present

burner

allows

for

a

systematic

examination

of

the

effects

of

product

stratification

and

heat

losses
.

It

should

enable

us

to

redraw

a

modified

Borghi

diagram

accounting

for

these

realities

and

redefine

the

boundaries

of

the

various

regimes
.

The

quenching

of

the

oxidation

layer,

which

is

not

currently

accounted

for

in

turbulent

combustion

theory,

appeared

to

be

a

critical

element

of

departure

from

the

flamelet

regime
.

Also

noteworthy

is

the

fact

that

the

achievable

experimental

conditions

for

these

premixed

flames

overlap

part

of

the

domain

of

IC

engines
.

OH planar laser induced fluorescence showing a wrinkled, singly
connected flame on the left, and a broken one on the right

Extended Borghi digram with the burner operational
domain in the dashed trapeze in the figure