Two Color Pyrometry

By measuring the brightness temperature using a disappearing filament pyrometer at two wavelengths, the blackbody (actual) temperature can be calculated. 

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Variations of flame temperatures with exhaust-gas recirculation. Flame temperature maps are obtained by processing images obtained from a combustion chamber of a heavy-duty diesel engine using two-color pyrometry. Images are taken at 2° after the TDC at 1200rpm low-load condition. 

Figure 42 shows the temperatures measured by two-color pyrometry for step changes in temperature compared with the true temperature and calculated temperatures based on the response characteristics of the detectors (time constant = 0.311 s). The response speed of the detectors in this case was too slow to follow the actual temperature decrease, but the temperature rise is reasonably well detected. Spjut and Bolsaitis reported that two-color temperatures are unreliable when the optical properties of the microparticle change during the experiment, but they showed that single-wavelength temperatures can yield consistent results and, with some caveats, are adequate for particle temperature measurement. 

Fig. 42. The response to a step increase (a) and a step decrease (b) in temperature of a laser-heated particle, from Spjut and Bolsaitis (1987). The data were obtained using two-color pyrometry, and the calculated curves are based on the response characteristics of the detectors.

Soot samples were obtained by use of a nitrogen-quench, porous-walled probe and Nucleopore filters (7). Gas phase hydrocarbons were collected by the porous probe as batch samples and analyzed by standard FID gas chromatography. Thermal measurements included gas temperature by radiation-corrected bare wire thermocouple, and soot temperature by Kurlbaum reversal (9, 10) and two color pyrometry (11). 

During high velocity CG/HW tests, samples were heated inductively to temperatures between 1100°C and 2500°C. Temperature measurements ofthe surface were also obtained by one-color and two-color pyrometry. Use of a two-color pyrometer was again employed to evaluate the spectral emittance ofthe oxidizing surface. Temperature gradients within the sample were measured by monitoring the temperature at the root of internal holes drilled to within 2.5 mm of the surface." ... 

The two-color method was applied to estimate two-dimensional (2D) contour of temperature and KL factor (KL factor is the factor used to indicate soot) distribution in the combustion flame. This two-color pyrometry system was set up by placing Vari lens that has the two different band-pass filters 488 nm in center wavelength (FWHM 11.3 nm) and 634 nm in center wavelength (FWHM 8.5 nm) for separating images to be two in front of an ICCD camera lens. The intensity data of both filters were used to calculate the tme temperature and KL factor. 

Pyrometry is thought to be the most feasible method to extract quantitative information from radiation spontaneously emitted from flames. Temperature distributions over large regions of the flame can be derived by applying the Plank law to every pixel of a CCD sensor. Two-color techniques are usually applied, due to its reduced sensitivity to uncertainties in emissivity or attenuation. Infrared cameras are used in most cases, as radiation levels are highest in this region of the spectrum [4-7]. Two channels of RGB video cameras have been also used in some works [8] although less accurate, this has the... 

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