FUNDAMENTALS OF TRANSIENT THERMAL-LIGHT ABSORPTION SPECTROSCOPY AND APPLICATION TO OPTICAL SENSING IN HCCI ENGINES

Abstract

A set of equations is developed for evaluating absorption spectroscopy based on thermal emitters such as lamps. The noise sources considered are photon (shot) noise and beating (wave interference) noise; signal-to-noise ratio limits for transient sensing with thermal light are also defined as a result of the analysis herein. The set of equations developed is used to evaluate three real absorption experiments: one which uses a thermal emitter, another which uses an external cavity diode laser, and one more which uses a supercontinuum source. In each experiment species concentration measurements are made in a homogenous charge compression ignition engine.