A study of the characteristics of slotted laminar jet diffusion flames in the presence-of non-uniform magnetic fields

The behavior of laminar jet diffusion flames in the presence of non-uniform magnetic fields has been investigated and the results of this experimental study are presented. It has long been recognized that magnetic fields can influence the behavior of laminar diffusion flames as a result of the paramagnetic and diamagnetic properties of the constituent gases. Using a magnet assembly consisting of neodymium iron boron magnets and gray steel prisms, a non-uniform upward decreasing magnetic field was applied to a laminar jet diffusion flame produced using a slotted burner port. The experimental results show that under certain conditions the application of the magnetic field decreased the flame height, prevented the flame from attaching to the prisms, increased the intensity of the flame, decreased the flow rate for which visible soot inception occurred, and increased the flow rate below which the flame extinguished. It was also observed that the degree to which these phenomena occur is proportional to the product of the magnetic induction times the gradient of the magnetic induction. A discussion as to the reasons for these observations is provided. In addition to traditionally defined dimensionless parameters, the previously defined magnetic Grashof number, the magnetic Froude number, and the ratio of the gravitationally induced buoyancy forces to the magnetically induced body forces are identified as key parameters for determining when a magnetic field will affect diffusion flame behavior. Using these dimensionless parameters, the experimental data was cast in a form that clearly indicated the universal nature of diffusion flame behavior in a non-uniform upward decreasing magnetic field. A power law curve fit to the dimensionless data is presented and discussed. (C) 2003 The Combustion Institute. All rights reserved.