Towards Pressure Measurements Using Filtered Rayleigh Scattering

Nonintrusive laser diagnostics are critical for the measurement of pressure, temperature, density, and velocity in a variety of aerospace and combustion applications. One of these diagnostics, filtered Rayleigh scattering (FRS), has been shown to be a useful in this regard. The primary advantage of FRS is that 1) it does not require particle seeding and 2) background scattering is strongly suppressed by the molecular vapor filter employed. Furthermore, the filter properties and collection angle can be adjusted such that the dependence on the thermal broadening of the Rayleigh scattering can be removed, thus making the signal proportional only to pressure via the ideal equation of state. We present a model of FRS for temperature insensitivity and pressure sensitivity with experimental results on the temperature insensitivity capabilities. Temperature insensitivity from 300-500 K is demonstrated in air, and a reduction in temperature sensitivity is demonstrated for a Hencken methane/air flame at ~1800 K by changing the observational angle and filter vapor pressure. Modelling of pressure shows that the pressure dependence of the FRS signal remains linear in these regimes.