ABSTRACT
Diesel particulate is regarded with suspicion as a pollutant having bad effect on respiratory organs of humankind. Particularly particles having diameters below 1 00 nm is reportedly accumulated in lung, and hence EPA of USA started a regulation in 1 997 to PM 2 , 5 emission, Diesel particulate is composed of hydrocarbons as sources for secondary particles and soot particles that occupy the major portion of diesel particulate. Current interest is mainly directed toward the measurement of number density distribution of such particles, but measuring the tail-out soot mass concentration is still important to achieve higher efficiency in combustion and improved control of soot emission. Among various measurement techniques, the classical extinction method is apparently a candidate for this purpose, and has been studied by several researchers [ 1 ,2] . However, both the effect of scattering on light extinction and the refractive index of soot still remain unclear, The authors propose a novel two-color extinction method to remove these two uncertainties by incorporating the two transmittances measured at two
