An experimental multiparameter investigation on the thermochemical structures of benchmark ethylene and propane counterflow diffusion flames and implications to their numerical modeling

Abstract

Counterflow diffusion flame is a canonical non-premixed flame configuration that is suitable for studying complex combustion chemistries such as soot formation. An important objective of such studies is to build predictive kinetic models. For validation of these models, complete and accurate experimental characterization of the flames are essential. Existing counterflow flame- based soot studies focused primarily on the determination of soot volume fraction, while simultaneous measurements of temperature, species concentrations and in particular flow fields were less common. Here we performed an experimental multiparameter investigation for a comprehensive characterization of the most important physical and chemical properties of four benchmark ethylene and propane counterflow flames, with the intention to provide data with sufficient details for the setup of corresponding numerical simulations and the evaluation of the resulted numerical data. Particle image velocimetry, tunable diode laser absorption spectrometry, microprobe sampling with gas chromatography, laser light extinction, laser induced incandescence are the techniques used respectively to measure flow fields, temperature, gas-phase species, and soot. Special attention was given to the effects of radial profiles of nozzle exit velocity on the quasi-one-dimensional counterflow simulation, whose results were compared against both the experiments and two-dimensional simulation. Probe effects on speciation were also quantitatively evaluated by comparing CO2 mole fraction as measured with the intrusive probe sampling as well as an independent optical technique. Our specially chosen ethylene and propane flames offered a direct experimental evidence that a flame producing higher concentration of benzene can have a significantly lower sooting tendency. It is hoped that the present comprehensive dataset can serve as a useful validation target for future high-fidelity gas-phase and soot models. It is also our intention that we provide sufficient details regarding the experimental apparatus and associated measurement techniques so that interested readers can reproduce our experimental data.