Measurement of the Mass Specific Extinction Coefficient for Acetylene and Ethene Smoke Using the Large Agglomerate Optics Facility

The mass specific extinction coefficient, rs, of smoke produced from acetylene and ethene fuel burned under laminar and turbulent conditions was measured using the Large Agglomerate Optics Facility. Key design features that enable a threefold reduction in the uncertainty compared with previous measurements include a 10-times longer pathlength, less than 0.05% drift in the light intensity ratio, steady-state smoke generation and dilution, accurate flow calibration, and more precise filter weight measurements. The measurements of rs are consistent with previous results obtained for smoke from a variety of fuels for both smalland large-scale fires. Specifically, the rs, of 7.80 m2/g for acetylene smoke produced by a turbulent flame using the new apparatus, is in excellent agreement with 7.82 m2/g as reported by Choi et al. [3] for the same fuel. However, these values are significantly larger than the value of 4.5 m2/g obtained from the study of Wu et al. [7] for acetylene smoke from turbulent flames. The reliability of the present experimental measurements is supported by an absolute calibration using an aerosol comprised of particles of known size, density, and refractive index. The measured values of rs in this study appear to be inconsistent with the values of the refractive index of smoke widely used in the combustion community. Measurements of the specific extinction coefficient for acetylene and ethene smoke indicate that rs depends on fuel type but displays little dependence on flame conditions (laminar or turbulent cases). For ethene smoke, the average specific extinction coefficient is 12% higher than for acetylene smoke. The larger rs may be due to a beam-shielding effect that is dependent on the primary particle size and the number of spheres comprising an agglomerate.