OPTICAL MEASUREMENT OF GAS-TURBINE ENGINE SOOT PARTICLE EFFLUENTS

This paper addresses optical-based techniques for measuring soot parti culate loading in the exhaust stream of gas turbine engines. The multi -angle scattering and multiwavelength extinction of light beams by ens embles of submicrometer soot particles was investigated as a diagnosti c means of inferring particle field characteristics. That is, the part icle size distribution function and particle number density were deduc ed using nit innovative downhill simplex inversion algorithm for fitti ng the deconvolved Mie-based scattering/extinction integral to the mea sured scattering/ extinction signals. In this work, the particle size distribution was characterized by the widely accepted two-parameter lo g-normal distribution function, which is fully defined with the specif ication of the mean particle diameter and the standard deviation of th e distribution. The accuracy and precision of the algorithm were evalu ated for soot particle applications by applying the technique to noise -perturbed synthetic data in which the signal noise component is obtai ned by Monte Carlo sampling of Gaussian distributed experimental error s of 4, 6, and 10 percent. The algorithm was shown to yield results ha ving an inaccuracy of less than 10 percent for the highest noise level s and an imprecision equal to or less than the experimental error. Mul ti-wavelength extinction experiments with a laboratory bench-top burne r yielded a mean particle diameter of 0.039 mu m and indicated that mo lecular absorption by organic vapor-phase molecules in the ultraviolet region should not significantly influence the measurements. A field d emonstration test was conducted on one of the JT-12D engines of a Sabr e Liner jet aircraft. This experiment yielded mean diameters of 0.040 mu m and 0.036 mu m and standard deviations of 0.032 mu m and 0.001 mu m for scattering and extinction methods, respectively. The total part iculate mass flow rate at idle was estimated to be 0.54 kg/h.