Research Projects

Project at a Glance

Project Status: complete

Title: Sensitivity of flame structure and particulate matter emissions to the operating configurations of a combustion wind tunnel

Principal Investigator / Author(s): Jenkins, B M

Contractor: UC Davis

Contract Number: A932-161


Research Program Area: Ecosystem & Multimedia Effects, Emissions Monitoring & Control

Topic Areas: Agriculture, Modeling, Stationary Sources


Abstract:

Particulate matter (PM) emissions and flame structure were investigated for spreading fires in a combustion wind tunnel using rice straw. Four operating configurations were investigated. The wind tunnel configuration was modified by extending or retracting an overhead adjustable ceiling, and by adding or removing a sheet steel floor directly underneath the fuel bed. PM emission factor varied from 0.7% of fuel mass for a 2 m s-1 wind speed and a configuration in which the ceiling was retracted and the floor was removed, to a low of 0.5% for a 3 m s-1 wind speed with the floor added and the ceiling extended to just ahead of the flame. Flame structure was examined through measurements of local temperatures, gas concentrations, and soot volume, the latter obtained by laser light extinction. Flame temperature profiles were altered substantially by changing wind speed and ceiling position, but peak flame temperatures were similar. Wind speed was a dominant parameter affecting the emission of particles. Higher wind speeds gave greater mixing rates, with reduced flame lengths and flame residence times and lower soot formation and PM emission. The floor was also observed to significantly influence particle emissions, possibly by restricting air flow through the smolder zone behind the fire, decreasing particle emission when present. Ceiling position by itself was not observed to significantly affect particle emission factor. Retracting the ceiling decreased streamwise air velocities and increased vertical velocities at the fire. Inlet velocity profiles with the ceiling retracted at low wind speed were distinctively different than at higher speeds or with the ceiling extended, suggesting flow separation due to an extremely adverse pressure gradient. Local turbulence intensities in the boundary layer were comparable with reported field values, as were surface roughness heights and friction velocities for the ceiling extended and the higher wind speed ceiling retracted configurations. Future experiments with spreading fires should make use of the ceiling extended high wind speed and ceiling retracted low wind speed configurations to evaluate the variability induced by the wind tunnel in emission factors of other species and with different fuels. Average values should be suitable for determinations of emission offset allowances.


 

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