Spectroscopic Methods and Visualization Applied to Combustion Diagnoses - Novel Combustion Concepts for Sustainable Energy Development - page 174

1.2 C 2 Vibrational Temperature (Kitagawa et al. 2003 )

We have developed a method for spectroscopic temperature measurements of gas
temperature during hydrocarbon combustion on the basis of two-color principle by
using the two-vibrational branches of the Swan band emission from C 2 radical
(Hino et al. 2004 ). The obtainable temperature is vibrational temperature of this
species.
The ratio of the intensities integrated over the two-color bands, I 1 /I 2, is given by
the following expression.

, X

X

A j k j

exp

ð E j kT vib Þ

I 1 = I 2 ¼ ð A i =k i Þ= exp ð E i = kT vib Þ ð 3 Þ

i j

is probability for spontaneous emission of vibrational
transition, T vib the vibrational temperature, and the subscripts i and j refer for the
individual vibrational spectrum line of the two bands, respectively. This method is
suitable for spectroscopic temperature measurements of non- /semi-radiant com-
bustion

Here, A is the Einstein '

flames during HITAC) of low equivalence
ratios and low carbon fuels such as natural gas.

fl flames (blue fl ames or green fl

2 Experimental

Figures 1 and 2 show the schematic diagrams of the regenerative test furnace
developed for preheating of steel slabs prior to rolling process and the measurement
system for spectroscopic temperature pro les, constructed in front of the furnace,

respectively.
The test furnace had been developed as a new type system in an NEDO project
and located at a steel making plant site of NKK Co. (currently JEF Co.) and has a
pair of burners which is alternatively switched at an interval, e.g., 1 min. The
exhausted gas, from the burner B, is fed to the heat accumulator of the partner
burner A. The fresh air and part of the exhausted gas are preheated through the
accumulator up to 1,200 C prior to combustion in the furnace. This high-tem-

perature air combustion (HITAC) (Kitagawa et al. 2003 ) has a great advantage of
capability to attain energy saving up to 30 % that is a green technology. The issues
taken into account include thermal NO x emission expected due to the excess
enthalpy during combustion. However, the HITAC combustion can be maintain
with low oxygen concentration down to 5 %, thus lowering NO x was expected.
Two types, diffusion and premixed combustions, were tested. Spectroscopical
pro

°

lings of the soot and C 2 temperature and chemical species were made in
conjunction with the NO x emission.
The image of the combustion

flame is converged by 1/18 through the lens, divided
into two paths, and each beam pass through the two-color (or wavelength) bandpass

fl