Water Vapor Absorption Thermometry for Practical Combustion Applications

Abstract

Thermometry in combustion applications by means of laser absorption spectroscopy is a well established diagnostic. The experimental simplicity and wealth of knowledge that can be readily gained from an absorption spectrum makes it often times the diagnostic of choice when interrogating the flow fields of practical combustion devices such as internal combustion engines. This project develops techniques for optimizing the design of absorption based sensors by providing strategies for selecting optimal wavelengths in order to improve thermometry. Descriptive relations are derived in order to predict the performance of an absorption based sensor and through numerical optimization, ideal selections of wavelengths can be made. Furthermore, this work applies novel hyperspectral lasers to practical combustion environments in order to infer gas properties based on direct absorption spectroscopy. The measurements are designed for high-speed (30 kHz and up) data rates of useful engineering parameters such as temperature and species concentration. Measurements have been performed across the cylinder of an optically accessible HCCI engine using a rapidly-swept (5 ?s measurement time) broad wavelength (1333-1377 nm) tunable laser. Temperature results were obtained at 100 kHz with 0.25% RMS precision at a temperature of 1970 K.