A Numerical Study of the Magnetic Influence on Coaxial Jets' Flow Upstream From Lifted Flames

Abstract

The authors conducted a numerical investigation of the laminar flow issuing from a methane/air coaxial burner submitted to a magnetic field. They intend to understand the mechanisms involved in the magnetic stabilization of the lifted flames. The model is based on the coupled equations of conservation of mass, species, and momentum in which the magnetic force acting on paramagnetic oxygen is introduced in the source term. A CFD code is used to solve the steady-state equations in an axisymmetric domain. Air jet velocity is shown to decrease locally in front of the magnetic gradient. Calculation of the stoichiometric radius reveals a lateral displacement of the stoichiometric line and a decrease of the fuel mass fraction gradient when the magnetic force is applied. These results explain the observed reduction of the liftoff height of flames under magnetic gradient due to an increase of the flame propagation velocity.

Lengths of Lifted Laminar Flames Under Vertical Magnetic Field Gradient

“…The magnetic field configuration and the distribution of the vertical magnetic gradient is the one used in the numerical calculations of cold flow described in Delmaere et al (2010). It corresponds to the magnetic field created by the magnets assembly in the experimental study of Gilard et al (2008).…”

“…Concerning the liftoff height, the influence of coflow velocity is significant since the coflow influences the concentration field by affecting entrainment of ambient air into the jet fuel. This entrainment is dependent on injection velocity of coaxial air (see Delmaere et al, 2010). Li et al (2010) conducted a numerical study to predict the liftoff for laminar jet diffusion flames of inert-diluted C 3 H 8 and CH 4 fuels.…”

“…They found that the magnetic field reduces the liftoff height. Delmaere et al (2010) developed a numerical study of the influence of a negative magnetic field gradient on the cold flow configuration between the exit of a coaxial nozzle and the lifted flame position. They have shown that the entrainment of air is modified when the magnetic field is applied.…”