Research On The Temperature Measurement For Combustion Field Based On Tunable Diode Laser Absorption Spectroscopy

Temperature is an extremely important physical quantity in combusiton diagnostics.Temperature measurement is of paramount importance to improve combustioneffciency to effectively use natural resources and minimize combustion-generatedpollution to reduce the impact on air quality. Traditionally, temperature fields aremeasured by thermocouples, which have some significant disadvantages: interferenceflow field, easily destructed, limited temperature range and lack of sufficient spatialand temporal resolution.Tunable diode laser absorption spectroscopy (TDLAS) can be used for measuringflow properties in combustors, which has many advantages over conventionalmeasurement techniques, such as non-intrusive, sensitive, high spatial and temporalresolution, large dynamic range and quantitative sensing of multiple parametersincluding gas temperature. This thesis study the temperature measurement forcombustion field using TDLAS, where water vapor is selected to be target species as amain combustion product. The specific contents and innovative research results aresummarized as follows:1. H2O line pair at1391.67nm and1468.89nm was selected according to transitionselection guidelines. TDLAS system was set up to measure the temperature ofcombustion field with two time division multiplexed lasers. Based on this system, theautomated processing algorithms of direct absorption spectral data was designed toachieve the inversion of temperature and concentration, and the measurementuncertainty was analyzed. The entire system was verified by experiments usingthermocouples and a Hencken flat flame burner. The temperature measured byTDLAS agreed with the radiation corrected thermocouple temperature, with thedeviation of less than4%.2. A tunable diode laser absorption tomography (TDLAT) algorithm was developedfor two-dimensional (2D) temperature reconstruction based on orthogonal grid. First,N×N path intersection temperature were caculated by Tikhonov regularizationalgorithm based on the2N (N≥3) path integrated line-of-sight (LOS) measurements ofcombustion field. Second, a smoothed, high resolution image was created by usingnatural bi-cubic spline interpolation to fill in values between grid points. The reconstruction noise immunity of our method increased by12%without accuracy losscompared with results of algebraic reconstruction algorithm (ART). The effects ofdifferent number of LOS measurement paths on the2D reconstruction results werefirst analyzed by means of numerical simulation of N×N uniform grid arrangement fortwo different temperature phantoms. N=5was determined to be the best option withconsidering reconstruction accuracy, the ability of anti-noise and system complexityand cost. The study is helpful for the real2D measurement system set up and actualapplication.A TDLAT system based on a3×3measurement path arrangement was setup and verified by flat flame furnace experiments using different CH4/air flow ratio.Error analysis showed that the the integral absorbance measurement uncertainty is themain reason resulting in the large temperature measurement error.3. The multi-line temperature measurement system based on rapid temperaturetuning technique was developed and validated. First, a model was established tocharacterize the relation between laser wavelength and the temperature of thethermistor integrated in the module. And the model was applied to dynamic thermaltuning on-line measurement to obtain more70H2O lines. Second,35transiton lineswere screened according to the improved spectral selection principle. Third, pathbinning method was proposed to obtain the temperature values of the sub-regionsalong the path. Fourth, the solution algorithm for temperature binning was improved,which used non-negative constraints Tikhonov regularization instead of non-negativeleast squares algorithm to deduce the probability density function of the flow fieldtemperature bins. Approximate stable non-uniform temperature field was constructedby alcohol lamp flame. Temperature binning, profile fitting, and path binning werecalculated respectively by the rapid temperature tuning multi-line thermometry. Theresults coincided with that measured by thermocouple and holographic interferometry.Therefore, the effectiveness of this method is verified for measuring approximatestable non-uniform temperature LOS distribution. The present study can be applied tothe temperature measurement of waste incineration, underground fire diagnosis, thehigh-temperature industrial process and other fields.