  Most studies of triple flames in counterflowing streams of fuel and oxidizer
have been focused on the symmetric problem in which the stoichiometric mixture
fraction is $1/2$. There then exist lean and rich premixed flames of roughly
equal strengths, with a diffusion flame trailing behind from the stoichiometric
point at which they meet. In the majority of realistic situations, however, the
stoichiometric mixture fraction departs appreciably from unity, typically being
quite small. With the objective of clarifying the influences of stoichiometry,
attention is focused on one of the simplest possible models, addressed here
mainly by numerical integration. When the stoichiometric mixture fraction
departs appreciably from $1/2$, one of the premixed wings is found to be
dominant to such an extent that the diffusion flame and the other premixed
flame are very weak by comparison. These curved, partially premixed flames are
expected to be relevant in realistic configurations. In addition, a simple
kinematic balance is shown to predict the shape of the front and the
propagation velocity reasonably well in the limit of low stretch and low
curvature.
