Stability limits of laminar flames

The other type of stability limit is associated with the mixture flow and its relationship to the laminar flame itself. This stability limit, which includes the phenomena of flashback, blowoff, and the onset of turbulence, describes the limitations of stabilizing a laminar flame in a real experimental situation. 

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R. Relce and R. Glavin. Influence of hydrodynamics and diffusion upon the stability limits of laminar premixed flames. /. Fluid Mech., 124 219-237, 1982. 

Laminar flame speed is one of the fundamental properties characterizing the global combustion rate of a fuel/ oxidizer mixture. Therefore, it frequently serves as the reference quantity in the study of the phenomena involving premixed flames, such as flammability limits, flame stabilization, blowoff, blowout, extinction, and turbulent combustion. Furthermore, it contains the information on the reaction mechanism in the high-temperature regime, in the presence of diffusive transport. Hence, at the global level, laminar flame-speed data have been widely used to validate a proposed chemical reaction mechanism. 

B. Fine, Stability limits and burning velocities of laminar hydrogen-air flames at reduced pressures. NACA TN 3833, 1956... 

The best fit of velocity exponent n in Hp °c ug (Figure 4.3.11) for pure propane (n-butane) is n = 4.733 (3.638), corresponding to Sc = 1.37 (1.61) from n = (2Sc-l)/ (Sc -1), which agreed well with the suggested value of Sc = 1.376 (1.524). The experimental liftoff height data are shown in Figure 4.3.12 for various nozzle diameters and partial air dilutions to fuel [53]. It can be observed that the air dilution to fuel does not alter Ypst and S° sf The results substantiated the role of tri-brachial flames on flame stabilization in laminar jets. As mentioned previously. Equation 4.3.5 limits the maximum velocity Ug for Sc > 1, which corresponds to blowout condition. 

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