Two-color pyrometry system to eliminate optical errors for spatially resolved measurements in flames

Two-color (2C) pyrometry has long been used to measure flame temperature and soot concentration from radiative emission in flames. While 2C pyrometry is not an absolute measurement in non-axisymmetric flames (such as diesel spray combustion), it is a desirable diagnostic for semi-quantitative or qualitative measurements since it requires minimal optical access and can utilize high-speed imaging to attain exceptional temporal and spatial resolutions. In this work, an improved optical configuration of 2C pyrometry is presented that (1) eliminates optical errors inherent in other designs and (2) uses off-the-shelf optics and a single camera. In particular, this work analyzes the impact of parallax and path length differences on the 2C pyrometry measurement and exemplifies how the present design eliminates associated errors by design rather than in post-processing. The theoretical range of measurements were generated a priori and overlaid with experimental data to illustrate the dynamic range over which 2C pyrometry can determine the soot concentration and temperature in theory and in practice.