Research On Measurement Technology Of Soot Concentration Based On Light Backscattering

In light backscattering soot particles concentration measurement technique, the soot concentration can be obtained by measurement of light backscattering intensity. At present, the measurement method faces an important problem that very weakly backscattering signal results in lower detection limit. The problem is resourced to insufficient acquaintance of backscattering characteristic of complicated shape soot particles swarm. Consequently, it is vital necessary to use proper theory and experiment analysis method to research in backscattering characteristic of complicated shape soot particles swarm and provide judgment for developing measurement instrument. This project was supported by the National Natural Science Foundation of China (No.61071036). Its intention was to study the backscattering measurement technology of soot particles concentration, which made this method be more suitable to particles concentration measurement online.This paper specifically focused on backscattering characteristic of complicated shape soot particles swarm and backscattering measurement experiment device. The research work was summarized as follows:1.Soot particles microanalysis and complex index of refraction measurementFirstly, Soot particles were collected on a practical boiler, its shape and size distribution was obtained and analyzed by scanning electron microscope (SEM). Secondly, the calculation of backscattering characteristic of soot particles is based on the acquaintance of its complex index of refraction, so we need to accurately measure complex index of refraction. In this paper, suspension turbid liquid transmission spectrum method and ellipsometry method were proposed. Compared with traditional KBr method, the two novel methods were more simply, and the result for visible light spectrum was directly obtained instead of the induced ruslut based on infrared spectrum, which established a foundation for precise calculation of backscattering characteristic of soot particles.2.Backscattering analysis of complicated shape soot single particleSoot particles SEM image demonstrates that its shapes are very complex. For solving backscattering characteristic of complicated shape soot particles, a novel method to construct complex shape of soot particles was proposed. To asymmetrical complex feature particle with smooth surface, a shape reconstructive method based on different kinds superellipsoids combination and overlap was brought forward. To asymmetrical complex feature particle with sudden change surface, a shape reconstructive method based on different cubes combination and overlap was proposed, thus any sharp surface particle can be reconstructed according to different position and height of cubes. As a result, backscattering characteristic of complicated shape soot particles has been obtained using T-matrix method. The result supported greatly analysis of backscattering of complex soot particles swarm.3.Backscattering analysis of complicated shape soot particles swarmIn the processing of soot particles swarm scattering characteristics, the shape of particle system was generally assumed to be spherical or quasi-spherical, which could decrease the complexity in calculating the non-spherical scattering traits In fact, most particle systems are non-spherical particles or even complex shape. On the basis of acquiring backscattering characteristics of single particle with complicated shape, a novel disposal using combination Monte Carlo method with T-matrix method was proposed to establish multi-scattering model of complex shape soot particles swarm, and calculated backscattering characteristics of the model. Moreover, a testable experiment device was designed. Simulation result offered theory basis for selecting light resource and detection angle reasonably.4.Research on instrument and experimentOn the basis of theory analysis, a novel backscattering soot concentration measurement instrument with four light resources was manufactured. The instrument was calibrated and tested repeatedly through a self-designed big soot flu pipe, and a practical measurement was realized on a 20t/h coal burning boiler, the result was compared with data of environmental protection department. At last, the Uncertainty of Instrument was analyzed.