Many studies have examined the stoichiometric lengths of laminar gas jet diffusion flames. However, these have emphasized normal flames of undiluted fuel burning in air. Many questions remain about the effects of fuel dilution, oxygen-enhanced combustion, and inverse flames. In addition, past experimental and computational work indicates that double blue zones are possible in hydrocarbon diffusion flames. However, much remains unknown about double blue zones in diffusion flames.

Thus, in this dissertation, the shape and double blue zones of the laminar co-flow jet diffusion flames are studied for more than 300 normal and inverse diffusion flames. Flame conditions including fuel type, reactant mole fraction, reactant flow rate, dilution agents, burner port material, burner port diameter, and flame Tad and Zst are varied. Chemiluminescence associated with excited species (C2*, CO2* CH*, and OH*) are measured through image deconvolution and broadband CO2* emission correction. Temperatures are measured with B-type thermocouples and TFP.

Nitrogen addition to the fuel and/or oxidizer is found to increase the stoichiometric lengths of both normal and inverse diffusion flames, but this effect is small at high reactant mole fraction. This counters previous assertions that inert addition to the fuel stream has a negligible effect on the lengths of normal diffusion flames. The analytical model of Roper is extended to these conditions by specifying the characteristic diffusivity to be the mean diffusivity of the fuel and oxidizer into stoichiometric products and a characteristic temperature that scales with the adiabatic flame temperature and the ambient temperature. The extended model correlates the measured lengths of normal and inverse flames with coefficients of determination of 0.87 for methane and 0.97 for propane.

Double blue zones, separated by up to 1.6 mm (and 0.9 mm) at the flame tip for IDFs (and NDFs), are observed in all the flames we measured. For both flame types, the blue zone toward the fuel side is rich and blue-green, while that toward the oxidizer side is stoichiometric, blue, and thicker. The rich zone results from emissions from CH* and C2*. The stoichiometric zone results from CO2* emissions and is coincident with the peak in OH*. All the deconvolved spectral emissive power peaks are higher in the IDF than in the NDF owing to higher scalar dissipation rates. The temperature profile of an NDF (and an IDF) was measured by B type thermocouple (and TFP). The result support the finding that the temperature peaks at the stoichiometric location for both NDFs and IDFs.