A two-color extinction method has been proposed that can measure the temporal mass concentration of soot aggregates in the diesel exhaust. Two laser beams in co-axia! alignment transmit a soot loaded exhaust gas flow, and the transmittance at each wavelength is detected simultaneously. The scattering-to-absorption ratio in the extinction coefficient for the soot aggregates was theoretically determined by the transmittance values measured at two wavelengths. The refractive index of the soot aggregates was also determined by a comparison of mass concentrations measured under steady operating conditions by both the extinction and a paper filter methods. Determining the scattering-to-absorption ratio in the extinction coefficient and the refractive index allowed significant improvement in the accuracy of the extinction method.
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