The Effects of Fuel and/or Oxidizer Composition on the Structure of a Laminar Fuel Jet in Hot Coflow under MILD Conditions

摘要

A study of the consequences of the composition of the fuel and/or oxidizer on spatial structure of the reaction zone from a diluted, preheated fuel jet in hot coflowing oxidizer in laminar flow has been performed both experimentally and numerically. The flames are burned using an axisymmetric laminar-jet-in-hot-coflow burner. Using methane as a base fuel, the effects of adding H_2, H_2/CO/CO_2 mixtures were studied; we also studied the effects of changing of the oxygen concentration in coflow. Radial distributions of temperature, major species and NO concentrations have been measured using spontaneous Raman and Laser Induced Fluorescence techniques. Computations are performed using detailed chemistry of GRI-Mech 3.0 and multicomponent mixture-averaged transport. Analysis of the data shows that the spatial development of the combustion has the characteristics of an "ordinary" coflow diffusion flame, besides the fact that changes in the temperature and major species concentrations in "ordinary" flame is approximately a factor of 10 higher than when using highly preheated and diluted reactants. As perhaps could be expected, the increase in O_2 concentration in coflow, as well as substituting of CH_4 by CH_4/H_2 mixture in fuel result in the decrease of the flame height. The NO LIF measurements show negligible NO formation, less than 2 ppm in the flames with ～3.5 mole% residual oxygen in the coflow, however, the increase in O_2 concentration in coflow leads to enlargement of NO formation, up to ～ 5 ppm. The numerical data are in reasonably good agreement with the measurements.