load and higher NOx emissions. Furthermore, lean premixed
combustion (LPC) has been shown to offer considerably higher
energy efficiency and lower pollutant emissions, but gas
turbines operating under LPC are more susceptible to
combustion instability and flashback [4]. Thus, understanding
the combustion characteristics of premixed syngas/air
mixtures over wide range of mixture compositions is essential
for the IGCC based power plant.
One aspect of previous studies on syngas combustion is the
measurement of laminar flame speed by using different
methods. Mclean et al. [5] measured the laminar flame speed
of stoichiometric H2/CO/air mixtures for H2/CO ratio of 5%/
95% and 50%/50% at atmospheric pressure using the spherically
propagating flame method. Subsequently, Brown et al. [6]
extended the above study to a full equivalence ratio range, but
they focused more on the effect of equivalence ratio and
hydrogen fraction on the Markstein length. Vagelopoulos and
Egolfopoulos studied the effect of hydrogen addition on premixed
counterflow CO/air flames. Laminar flame speeds and
extinction strain rate were determined by Laser Doppler
Velocimetry (LDV) technique [7], and the result showed that
small amount of hydrogen addition would increase the
laminar flame speed and extend the extinction limit. Other
studies also reported the combustion characteristics of syngas
mixture, like laminar burning velocity and flame stability,
using the methods of constant-pressure spherical flames and
counter-flow flames [8e10]. Bunsen flame configuration and
flame cone angle was also widely used to measure the flame
speed of syngas/air mixtures. Bouvet et al. [11] recently
measured the laminar flame speed of H2/CO/air mixtures
using Bunsen flame configuration and OH* chemiluminescence
technique. They proposed a flame speed
correlation for lean mixtures with hydrogen fraction in the
fuel blends ranging from 10% to 70%. Dong et al. [12] measured
the laminar flame speed over wide range of equivalence ratios
and hydrogen fractions using the Bunsen burner and a CCD
camera. However, it is very hard to precisely detect the edge of
the reaction zone from CCD camera image due to the weak
spontaneous emission signal and the systematic errors
caused by the rounded flame tip. Planar laser-induced fluorescence
(PLIF) can detect the reaction zone through OH
radical emissions with high spatial resolution and high signalto-
noise ratio [13e17]. He et al. [18] measured the laminar
flame speeds of lean premixed syngas/air mixtures using
Bunsen flame configuration and PLIF technique. However,
they only focus on the fuel-lean mixtures with low hydrogen