Considerations for the application of CARS to turbulent reacting flows

Abstract

Coherent anti-Stokes Raman spectroscopy (CARS) has matured considerably over recent years and is experiencing widespread application in fundamental and practical combustion situations. Its utilization in turbulent reacting flows is far from routine, however, and several problem areas need to be addressed and refined. This paper reviews these problems and assesses the status of current and proposed solution approaches. Due to its highly nonlinear dependence on temperature and species concentration, CARS measurements in time-varying environments necessitate assembly of “instantaneous” single-pulse measurement histograms, even to extract time-averaged properties. A number of factors contribute to distortion of single pulse CARS spectra and, thus, measurement inaccuracy; various improvement strategies will be evaluated. The problem of absolute concentration measurements at low and high Mach numbers in refracting and attenuating media will be discussed. The paper concludes with a description of an approach to permit CARS measurements of several species simultaneously in a single laser pulse.