COL 11(5), 053001(2013) CHINESE OPTICS LETTERS May 10, 2013
Calibration method for 2D instantaneous OH-PLIF
temperature measure ments in flame
Shuang Chen (
WWW
)
∗
, Tie Su (
), Furong Yang (
LLL
JJJ
),
Long Zhang (
ÜÜÜ
999
), and Yaobang Zheng (
xxx
ǑǑǑ
)
China Aerodynamics Research and Development Center, Mianyang 621000, China
∗
Corresponding author: chenshuang827@gmail.com
Received October 23, 2012; accepted December 20, 2012; posted online March 28, 2013
Noninvasive technology for measuring instantaneously two-dimensional (2D) temperature distributions of
flame using two-color planar laser induced fluorescence (PLIF) of OH is investigated. A calibration method
is researched and d eveloped. This method is based on the calibration experiments with a laminar premixed
flame and thermocouple, and avoids complex calculation and uncertainty of the spectrum parameters.
Measurements for a flat burner at ambient temperature under atmospheric pressure are also presented;
calibration results are used to diagnose a supersonic combustion in scramjet combustor. The conclusion
indicates that this method is useful, and a better precision of calibration can be acquired by correcting the
line shapes of the spectral lines and lasers.
OCIS codes: 300.2530, 300.6280, 300.6360, 300.6540.
doi: 10.3788/COL201311.053001.
Planar laser induced fluorescence (PLIF) is an attrac-
tive flow-measurement technique in combustion and high-
sp e ed aerodynamics resea rch. This laser-bas e d diagnos-
tics is advantageous in some special and severe environ-
ments and flow fields, because they are nonintrusive and
robust. PLIF can measure two-dimensional (2D) conce n-
trations of molecules, such as OH, CH, NO, and CO
[1−5]
.
Moreover, the two-color PLIF methods offer the advan-
tage of 2D temperature measurements that yield infor-
mation ab out special structure and temperature distr i-
butions with high temporal and spatial re solution
[6−8]
.
OH is a n impor tant reactive intermediate in combustion.
Thus, using OH radicals as indicator is a perfect choice
because of its abundant concentration at high tempera-
ture and its spectroscopic characters.
Several thermometry methods based on laser and spec-
tra technique have been developed. Especially, Seitzman
et al. have develope d temperature measurements with
OH-PLIF
[6,7]
. In their representative work, the temper-
ature distribution of flame has bee n acquired by laser-
induced fluorescence (LIF) imaging and calculation with
the data of the two spectrum lines selected
[8]
. In the re-
cent years, several PLIF-thermometry works similar to
the results in Refs. [6-8] have been pe rformed in va rious
combustion experiments
[9−12]
. However, the spectrum
data used are difficult to confirm and correct in com-
plex combustion environment, there by influencing the
accuracy of the OH-PLIF measurement. T herefore, an
effective calibration method is needed.
In this letter, a double-pulse PLIF e xpe riment system
is set up to study the two-color OH-PLIF thermometry
technique. A calibration method for this technique has
been developed using the flat flame burner and thermo-
couple. Furthermo re, the calibration experimental re-
sults are used to correc t the transient temperature dis-
tribution of a turbulent flame.
According to the OH-PLIF principle
[13]
, the total flu-
orescence signal intensity I
f
for the line, obtained fr om
exciting with a laser intensity I
l
from level i in the ground
state to level i
∗
in the excited state, is given by
I
f
= α · N
i
· B
ii
∗
· I
l
· g · η, (1)
where α is an instrumental constant co mprising light
collection efficiency, filter and detector quantum
efficiencies, electronic gain, etc.; B
ii
∗
is the absorption
coefficient; N
i
is the population in the level i; g is the
overlap integral of the absor ption line shapes g
abs
and
laser line shapes g
laser
, and given by
g(ν
l
, ν
a
) =
Z
+∞
−∞
g
abs
(ν, ν
l
)g
laser
(ν, ν
a
)dν, (2)
where ν is the frequency, and ν
l
and ν
a
are the center
frequencies of the lines above. The quantum yield η is
known as A/(A + Q), a nd A is the effective rate of spon-
taneous emission for a ll directly and indirectly populated
states. Similarly, Q is the total electronic quenching ra te
of the excited states. For the two-color PLIF thermome-
try technique, a ratio of signals is taken, exciting first one
transition, and then another from the same lower vibra-
tional level but a different ro tational state. The signals
are formed by the summation of the two LIF signals cap-
tured at the same time, which are given by
I
(1)
f
= α
(1)
· N
(1)
i
· B
(1)
i1
· I
(1)
l
· g
(1)
· η
(1)
, (3)
I
(2)
f
= α
(2)
· N
(2)
j
· B
(2)
j2
· I
(2)
l
· g
(2)
· η
(2)
, (4)
where one is the excited state 1 after excitation from the
ground state level i , and the other is the state 2 excited
from level j. The ratio of the ground state populations
N
i
and N
j
according to Boltzmann statistics is given by
N
i
N
j
=
2J
i
+ 1
2J
j
+ 1
· e
−
(E
i
−E
j
)
kT
, (5)
where (2J + 1) and E ar e the degeneracy and energy of
a ground state with rotational quantum number J, re -
sp e ctively, and T is the temperature. Combining these
three equations yields the des ired relatio nship between
the temperature and the ratio of the fluoresc e nce signals
1671-7694/2013/053001(4) 053001-1
c
2013 Chinese Optics Letters