Relative Polycyclic Aromatic Hydrocarbon Concentrations in Unsteady Counterflow Diffusion Flames

Frequency Response of Counter Flow Diffusion Flames to Strain Rate Harmonic Oscillations

“…Moreover the maximum frequency for which the flame response can be considered quasi-steady for larger PAHs. These results are in agreement with experimental and numerical investigations performed by several authors (Egolfopoulos et al, 1996;Xiao et al, 2005). The nondimensional Stokes' number (η K ) can be useful to better understand the frequency response of counter flow diffusion flames:…”

“…The counter flow diffusion flames numerically simulated in this paper were experimentally investigated by (Xiao et al, 2005). The oxidizer and the fuel tubes are 25.4 mm in diameter and have a 12.7 mm separation distance; the inlet temperatures are 298K.…”

“…In Figure 3 the numerical results obtained for Flame II are summarized in terms of temperature and PAH mole fraction peak values. Following (Xiao et al, 2005), PAHs were grouped in three classes. Class A includes one-and two-rings PAHs, Class B three-and four-rings PAHs and Class C PAHs with more than four rings.…”

“…If Reynolds number is sufficiently high, a large range of eddy sizes is expected, in which the characteristic eddy turn-over times become comparable with the diffusion time in the laminar flamelet (Im et al, 2000). In such conditions, the unsteadiness begins to show its effects on the characteristics of the laminar flamelets and consequently it becomes important to understand the unsteady effects and if information obtained in steady state conditions can be extended to unsteady conditions (Haworth et al, 1988;Barlow et al, 1992;Egolfopoulos et al, 1996;Xiao et al, 2005). From a numerical point of view the introduction of unsteadiness in combustion is a challenge because of the strong coupling between the time and spatial scales of convection, diffusion and reaction.…”

“…As a first step, many authors suggested to perform this kind of investigations by exposing the laminar flames to far-field harmonic oscillations in the strain rate, using a large range of frequencies (Im et al, 2000;Egolfopoulos et al, 1996;Decroix et al, 1999;. The effects of unsteadiness on counterflow diffusion flames were experimentally (Xiao et al, 2005;Decroix et al, 1999;, Welle et al, 2000 and numerically (Im et al, 2000;Egolfopoulos et al, 1996, Stahl et al, 1991Cuoci et al, 2008) investigated by several authors. From both experimental and numerical results, it seems evident that the assumption of quasi-steady response in some conditions is not appropriate.…”