Abstract
A method to determine the Schmidt number of fuel is proposed from the behavior of laminar lifted jet flames. Based on the observation of a laminar lifted flame edge, the flame stabilization point is located along the stoichiometric contour in the mixing layer of fuel and air in laminar jets, since a tribrachial (triple) flame structure exists which is composed of a diffusion flame, a rich premixed flame and a lean premixed flame, all extending from a single location. For the flame edge to be stationary, the axial velocity at the edge should balance with the propagation speed of the tribrachial flame. Since the region between the flame stabilization point and the nozzle exit can be treated as a cold jet, the jet theory of momentum and species can be applied to obtain the correlation of liftoff height with jet velocity and nozzle diameter of
H
L
∝
d
2
u
o
(
2
S
c
F
−
1
)
/
(
S
c
F
−
1
)
. Using this relation, the mixture of fuels having
Sc<1 and
Sc>1 are tested. The dependence of liftoff height on jet velocity is curve-fitted to extract the effective Schmidt number of mixed fuels. Experimentally determined Schmidt numbers agree satisfactorily with the theoretical predictions from the kinetic theory.