A CONCEPT FOR IN-SITU DETERMINATION OF REFRACTIVE AND ABSORPTIVE INDICES OF SOOT PARTICLES

MANY COMBUSTION EXPERIMENTS INVOLVING PARTICLE SIZING AND RADIATION MEASUREMENT REQUIRE AN ACCURATE KNOWLEDGE OF THE REFRACTIVE (N) AND ABSORPTION (K) INDICES OF SOOT. EVEN THOUGH SOOT IS A COMPLEX HYDROCARBON WITH A PARTICULARLY HIGH C:H MASS RATIO, VALUES FOR N AND K FOR CARBON ARE OFTENUSED AS BEING EQUIVALENT FOR SOOT. LITERATURE VALUES OF N AND K FOR SOOT AND CARBON SHOW WIDE SCATTER: 1.40<N<2.6, 0.43<K<1.4. THESE VALUES WERE QUOTED WITHIN QUITE A NARROW WAVELENGTH RANGE (430<LAMBDA<550NM), WHERE N AND K ARE ALMOST CONSTANT. ALSO, DUE TO THE COMPLEXITY OF THE SOOT FORMATION PROCESS, IT IS LIKELY THAT N AND K WILL CHANGE WITHIN DIFFERENT REGIONS OF A GIVEN FLAME. USING THE COMBINATION OF POWER SPECTRA AND/OR AUTOCORRELATION TECHNIQUES WITH SCATTERING AND EXTINCTION, THE PROPOSED RESEARCH PROJECT IS SUGGESTED AS A CONCEPT FOR AN IN-SITU METHOD IN WHICH AN ASSESSMENT OF N AND K CAN BE MADE DIRECTLY.