Enhancement of flame blowout limits by the use of swirl

Abstract

The blowout limits of a number of swirl stabilized flames were measured and the trends are explained by applying the concepts proposed in recent flame blowout theories, which previously have been applied only to non-swirling flames. It is shown that swirl flame blowout limits can be compared to wellknown limits for non-swirling simple diffusion flames by using the proper nondimensional parameter, i.e., the inverse DamkohlerUnlike most previous work. four parameters were systematically varied: the fuel tube diameter (dF), the fuel type and thus reaction rate, which is related to the maximum laminar burning velocity (SL), the coaxial air velocity (UA), and the swirl number.Results show that the maximum fuel velocity (UF) and thus the maximum heat release rate for a swirl flame is as much as four times larger than that for a non-swirling flame. Blowout velocity (UF) increases with burner size (dFj and laminar burning velocity squared (SL2); this is similar to non-swirling flames except that a new parameter that includes swirl number must be added. The major reason why swirl increases the stability of a flame is because of a flame-vortex interaction. The toroidal recirculation vortex reduces the centerline velocity below that of a non-swirling flame and the analysis shows that this is strongly stabilizing.

Experimental study and RANS calculation on velocity and temperature of a kerosene-fueled swirl laboratory combustor with and without centerbody air injection

“…Such a small change of swirl number cannot have significant influence, as demonstrated in the present simulation. Similar conclusions were also reported by [31].…”

Prediction of Global Extinction Conditions and Dynamics in Swirling Non-premixed Flames Using LES/CMC Modelling

“…The blow-out limits (i.e. air versus fuel bulk velocities) at both fuel rich and lean compositions in a swirl burner from the University of Michigan (without appreciable bluff body effects) were measured and it is found that the operating conditions for stable swirling flames were extended relative to the nonswirl counterparts, although the extent depends on the swirl number [21,22]. The results also showed that the compact and strongly recirculating flames, instead of lift-off, can only been observed close to lean blow-out [21].…”

Heat transfer characteristics of dual swirling flame impinging on a flat surface

“…These recirculation bubbles result in enhancement of fuel-air mixing that further results in reduction of flame length (nearly five-fold) compared to simple non-swirling flame jet [36e38]. Further, it has also been reported in the literature that the recirculation zone increases the stability of the swirling flame (nearly five times) than the corresponding non-swirling flame [32,39]. In some of the cases, lifted stable swirling flames were also observed at sufficiently high swirl intensities [40e42].…”