Nonintrusive optical measurements of aircraft engine exhaust emissions and comparison with standard intrusive techniques.

Nonintrusive systems for the measurement on test rigs of aeroengine exhaust emissions required for engine certification (CO, NO(x), total unburned hydrocarbon, and smoke), together with CO(2) and temperature have been developed. These results have been compared with current certified intrusive measurements on an engine test. A spectroscopic database and data-analysis software has been developed to enable Fourier-transform Infrared measurement of concentrations of molecular species. CO(2), CO, and NO data showed agreement with intrusive techniques of approximately ?30%. A narrow-band spectroscopic device was used to measure CO(2) (with deviations of less than ?10% from the intrusive measurement), whereas laser-induced incandescence was used to measure particles. Future improvements to allow for the commercial use of the nonintrusive systems have been identified and the methods are applicable to any measurement of combustion emissions.

Calibration of a Fourier transform spectrometer using three blackbody sources.

A procedure to calibrate a Fourier transform spectrometer is presented. Blackbody sources of three different temperatures are used to eliminate errors in the calibration that result from the limited accuracy of the temperature measurement of the calibration sources. With three spectra of blackbodies it is possible to assume that the temperatures are unknown variables as are the parameters of the functions that describe the spectrometer. A nonlinear Gaussian balancing calculation is used to determine these unknown variables and to minimize the influence of noise. A comparison between the results obtained with this method and a conventional calibration procedure is presented.

Michelson interferometer with a rotating retroreflector: a laboratory model for environmental monitoring.

Designed for atmospheric pollution monitoring, a breadboard model of a new Michelson interferometer has been developed. It utilizes a nutating retroreflector to generate alterations in the geometrical and optical paths. The forward-backward stop-and-go movement of a reflecting element of conventional Michelson interferometers is thus replaced by a continuous rotation. At this state the instrument employs a 6.3-cm (2.5-in.) diam rotating retroreflector, a ZnSe beam splitter, and a HgCdTe detector at liquid nitrogen temperature, sensitive in the 8-14-microm band. It allows spectral resolutions of up to 2 cm(-1). The device is linked via an analog digital interface to a desktop computer which performs interferometer control, data acquisition, Fourier transform, and display of the spectra.