No abstract

The optical emissions from a turbulent, nonpremixed, liquid fueled (n-heptane) combustor were investigated using two optical imaging systems: a high spectral resolution (~0.3 nm), single wavelength system; and a low resolution (~5 nm), multi-wavelength system intended to mimic the response of a practical sensor. The goal was to develop signal interpretation strategies that would allow an optical sensor system to monitor needed properties in liquid-fueled combustors and engines. The research focused on the chemiluminescent emissions from OH*, CH*, and C 2 *. Data were acquired for a range of fuel and air flow rates (equivalence ratios 0.6-1.3), and for radial slices through the nominally axisymmetric combustor over the complete combustor length. Without correction, both OH* and CH* emission were found to be good indicators of heat release rate only over a narrow band of lean equivalence ratios. In addition, OH* provides information on the postcombustion zone conditions. A nearly linear relationship was found between the overall equivalence ratio of the combustor and the ratio of the emission integrated over the combustor volume from two radical species, with the ratio C 2 */OH* exhibiting the greatest sensitivity. The correlation was also applied to estimate the radially averaged equivalence ratio of the reaction zone along the length of the combustor. With the multiwavelength sensor set to simultaneously monitor the broadband background from the flame, its background corrected output agreed well with the high spectral resolution results, suggesting that a properly designed optical sensor system would be capable of determining local combustor conditions such as reaction zone equivalence ratio and heat release rate.