Selection of spectral lines for combustion diagnostics.

This paper reports part of our effort to develop practical systematic techniques for measurements in high temperature gases using laser absorption spectroscopy. We present a brief summary of the analysis techniques we have developed for line-of-sight measurements. We show that the accuracy of the absorption measurement in a given experiment is largely determined by the spectral lines used for the measurement. Thus the selection of spectral lines is critical for the success of a diagnostic measurement. In this paper, we propose a set of criteria for selecting spectral transitions for temperature and concentration measurements at various experimental conditions. They include the requirements for spectral line resolution, absorption strength, sensitivity, and insensitivity to systematic errors. These rules could be implemented in an expert system. A simplified version of the selection criteria was implemented in a PASCAL program. The capabilities of the program are demonstrated by the selection of absorption transitions of CO for simultaneous temperature and species concentration measurements at several experimental conditions. The criteria and program may be readily extended to other spectroscopic techniques such as laser-induced fluorescence.