Analysis of Uncertainties in Infrared Camera Measurements of a Turbofan Engine in an Altitude Test Cell

摘要

This research investigated the uncertainties in measuring the IR signature of a General Electric F110-GE-129 turbofan engine inside an altitude test cell. The requirements for the measurement system include the intensity and radiance of the engine surfaces in three bands of operation, two Medium Wave IR (MWIR) bands and one Long Wave IR (LWIR) band. The altitude test cell provides a venue for measuring the IR signature in simulated altitude operation, but the imaging process is laden with measurement uncertainty due to stray radiation from the facility structure, hot exhaust gases, and the measurement equipment itself. The atmosphere and a protective ZnSe window that shields the camera from the hot engine exhaust also introduce measurement uncertainty due to attenuation. Consequently, post-processing of the signature data is necessary to recover the engine signal, but they inject an additional level of measurement uncertainty into the imaging process. To assess the measurement uncertainty, a radiometric model of the altitude test cell is formulated. Specific measurement conditions at which the stray radiation is 5% or less of the total radiation are then derived, thereby decreasing the necessity for post-processing correction factors. These conditions are derived for the 3-4, 4.5-5, 8-9, and 8-12 micron bands using a parametric analysis. The fidelity of the model is increased by the inclusion of experimental data from the ZnSe window.