There has been relatively little work concerning high pressure syngas flames. McLean et al. (1994) and Vagelopoulos and Egolfopoulos (1998) reported premixed flame speeds at pressures from atmospheric to a few atmospheres. Burke et al. (2007) examined the effect of CO2 on burning velocity of spherically expanding flames at p = 1.0 and 10 atm using a 25%H2-75%CO mixture with 12.5%O2-87.5%He oxidizer. Sun et al. (2005) reported laminar flame speeds for

CO/H2/air and CO/H2/O2/He mixtures for pressures up to 40 atmospheres using the constant- pressure spherical flame technique. A kinetic model was also developed using the latest available thermo-transport and kinetic data (Park et al., 2004; Ouimette, 2009). The mechanism was validated against the measured flame speeds, non-premixed counter flow ignition temperatures, concentration profiles in a flow reactor, and ignition data from shock tube experiments. Figure 2.16 from their study shows the measured and predicted laminar flame speeds plotted versus Ф for CO/H2/O2/He mixtures at different CO/H2 ratios, and pressures of 5-40 atm.

Predictions are based on their kinetic model and that reported by Davis et al. (2005). As expected, the flame speed increases with increasing H2 content, and decreases with increasing pressure. Overall, there is good agreement between the predictions and measurements, although both models exhibit discrepancies, whichmay be attributed to uncertainties in kinetic and transport data. Thus, further studies are warranted for high-pressure syngas flames over a range of com­bustion regimes, including non-premixed and partially premixed combustion, and using different burners.

Studies on turbulent syngas flames have focused on the determination of turbulent flame speeds (ST) (Chase et al., 1951; Kee et al., 1995; Daniele, 2011). While ST can be defined in multiple ways, it is often based on a global consumption speed (Venkateswaran et al., 2011) and is presented in terms of the normalized flame speed (ST/SL) as a function of turbulence intensity, fuel composition and other parameters. Daniele et al. (2011) considered the reaction zones regime and examined the effects of pressure and syngas composition on the turbulent flame speed. Correlations were developed for ST / SL as a function of normalized parameters representing the effects of turbulence intensity, integral length scale, pressure, and temperature.

The increase of ST/SL with increasing pressure and H2 content was attributed to the thermo­diffusive and hydrodynamic instabilities. Venkateswaran et al. (2011) reported measurements of global turbulent flame speeds using a Bunsen burner, and examined the effects of Ф, syngas composition, mean flow velocity, and turbulence intensity. Consistent with other studies, the flame speed was found to exhibit sensitivity to fuel composition over a wide range of turbulence intensity, increasing significantly with the increase in H2 content. The data were further analyzed to develop flame speed correlations, indicating the effects of thermo-diffusive instabilities through negative Markstein lengths.