A two-wavelength ethylene-absorption temperature diagnostic

Recent high-temperature absorption cross-section measurements of ethylene have revealed spectral features with strong sensitivity to temperature. Motivated by these observations, this work presents a novel two-wavelength laser absorption diagnostic for inferring temperature from the ethylene spectrum. Two CO₂ gas laser wavelengths, 10.532 μm and 10.591 μm, were systematically chosen for their cross-section strengths and the temperature sensitivity of their absorbance ratio. Cross-sections at each wavelength and absorbance ratio measurements were collected over conditions 418-1671 K, 0.3-4.3 atm in a shock tube. The absorbance ratio was found to be insensitive to pressure between 1.1 atm and 4.3 atm, and a correlation was developed to describe the ratio as a function of temperature. At lower pressures, the correlation incorporates an additional pressure factor. The diagnostic was used to study the shock tube pyrolysis of ethane at 1330 K and 2.2 atm, and further applications are suggested.