Application of the steady-state and unsteady-state lasers in reconstructing the geometrical characteristic parameters of soot fractal aggregates

摘要

The unsteady-state laser, i.e. time-domain (TD) and frequency-domain (FD) lasers, and the steady-state (SS) laser are employed as the measurement lasers to reconstruct the geometrical characteristic parameters of soot fractal aggregates, i.e. the root mean square radius R_g and fractal dimension D_f. The direct problems are solved by the finite volume method and Rayleigh- Debye-Gans fractal aggregate method, while an improved artificial bee colony algorithm is used as the inverse problem algorithm. The sensitivity analysis is employed to study the effective sampling region of the TD and FD laser measurement signals, and the results show that the timeresolved signals selected within [L, 0.5L+ct_p] for the TD laser and the dimensionless frequency selected within [0.5, 5] for the FD laser are conducive to improving the retrieval accuracy. Then, the geometrical characteristic parameters of soot fractal aggregates are retrieved by using different measurement lasers, and the results reveal that the retrieval accuracy can be ensured by using the TD laser measurement technique. Moreover, the retrieval accuracy and robustness of R_g are better than those of D_f. All the studies in the present manuscript supply an application plat of the laser measurement techniques in reconstructing the geometrical characteristic parameters of soot fractal aggregates.