Environmental Engineering Reference
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have also shown similar trend. For brevity, the results are not included here, and the
details may be found at Chaudhari (
2011
).
3.1 Flame Color: LBO Predictor
A LBO prediction strategy based solely on the
flame color variation was proposed
by the authors (Chaudhari
2011
; Chaudhari et al.
2013
). The technique is based on
fl
fl
flame images captured by color CCD or CMOS sensor. Data were acquired for
three different air
fl
ow rates (Q
air
) for fuel supply to each of the
five premixing
lengths (L
fuel
). At each equivalence ratio (
Φ
) condition, four photographs of the
fl
flame modes were taken by a digital SLR camera. Each color image acquired from
the SLR camera was analyzed using MATLAB
to obtain a color metric used for
LBO prediction. Each pixel in a color image is mapped as a vector of three intensity
components, i.e.,
®
8
<
9
=
I
r
ð
x
;
y
Þ
I
g
ð
x
;
y
Þ
I
b
ð
x
;
y
Þ
I
ð
x
;
y
Þ
¼
ð
1
Þ
:
;
where I
r
, I
g
,andI
b
refer to the red, green, and blue components, respectively, of the
intensity of the corresponding pixel. This is a result of the presence of only these
three colors on the Bayer filter used in conventional digital cameras. Considering
that changes in image color range from red to blue in a
fl
flame as LBO is approached,
which is illustrated in Fig.
10
where
P
x
;
y
I
r
ð
x
;
y
Þ
and
P
x
;
y
I
b
ð
x
;
y
Þ
represent the
mean value of red and blue color intensities determined from our frames captured at
each equivalence ratio (
) value for Q
air
= 80 LPM, L
fuel
= 35 cm. The two
quantities, respectively, decrease and increase monotonously with decreasing
equivalence ratio (
Φ
). Based on this color variation, we propose LBO detection
metric in the form of
Φ
X
X
c
¼
I
r
ð
x
;
y
Þ=
I
b
ð
x
;
y
Þ
ð
2
Þ
x
;
y
x
;
y
Determination of
is computationally inexpensive and can be performed on a
γ
real-time basis.
We compared the
flame color variation detected by color camera with spec-
trometer results. Spectrometer captured the electromagnetic emission of
fl
ame
simultaneously with the color camera at different equivalence ratio conditions.
Figure
11
shows the visible electromagnetic spectrum of
fl
flame emission for dif-
ferent operating conditions obtained when the combustor operated from stoichi-
ometric condition until blowout
fl
Φ
LBO
= 1.49 (represent
stoichiometric condition of combustor) the dominating wavelength of
takes place. At
/
Ф
flame emis-
sion is observed to be around 700 nm which is close to the standard red color
fl
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