Mark Daniel D'Agostini

A Study of the Influence of Oxygen Index on Soot, Radiation, and Emission Characteristics of Turbulent Jet Flames

Many combustion applications benefit from the use of oxygen-enriched air or pure oxygen as an oxidizer. To provide guidance in the use of oxygen-enriched or oxy-fuel combustion, research was conducted to understand how key parameters affect the radiation and emissions characteristics of jet flames for a range of oxygen indices from 21% (air) to 100% (pure O 2 ). Experiments were conducted on simple jet flames created by fuel issuing from a 3-mm i.d. straight tube into a low-velocity oxidizer stream for a variety of conditions. In addition to O 2 content of the oxidizer, fuel jet velocity and fuel type were varied. Laser light extinction was used to measure mean soot volume fractions as functions of axial distance. Other measurements include axial profiles of total radiant heat flux and NO x and CO emission indices. Results of these experiments were compared with predictions from a modified version of the two-stage Lagrangian (TSL) model of Broadwell and Lutz. The TSL code was modified by the incorporation of a detailed soot model from Frenklach et al. and the addition of a radiation submodel that accounts for both gas-band and soot blackbody radiation. In general, the TSL model captures the trends observed in the experiments for various parameters as functions of oxygen index, fuel type, and fuel-jet velocity, although absolute values are not predicted with engineering accuracy. The model was also exercised to predict the soot contribution to the total radiant heat transfer with soot volume fractions adjusted to be more representative of experimentally measured values.

EFFECT OF REACTANT INITIAL TEMPERATURE ON METHANE/OXYGEN DIFFUSION FLAME STABILITY IN A FURNACE

ABSTRACT An investigation was performed to examine the initial temperature effect of gaseous reactants on the stability of a methane/oxygen diffusion flame for a constant oxidizer-to-fuel mass ratio ((O/F)mass)of 1.3 in a furnace. Gaseous reactants were individually heated and then ignited by an ethane/oxygen torch. Stability maps were developed based on data from over 130 combustion tests with initial reactant temperatures ranging from 298 to 398 K. As oxidizer initial temperature was increased, the Reynolds number and ignition time decreased, resulting in a quicker transition from a stable flame regime to an unstable flame regime. The diffusion flame standoff distance from the injector exit plane rose and fell as the oxidizer temperature was further increased. This indicates that for shorter ignition times and higher flow velocities associated with hotter reactants, diffusion flames achieved more efficient transverse mixing in the jet and thus minimized their instability associated with large standoff distances.