Analysis of aircraft exhausts with Fourier-transform infrared emission spectroscopy

Because of the worldwide growth in air traffic and its increasing effects on the atmospheric environment, it is necessary to quantify the direct aircraft emissions at all altitudes. In this study Fourier-transform infrared emission spectroscopy as a remote-sensing multi-component-analyzing technique for aircraft exhausts was investigated at ground level with a double pendulum interferometer and a line-by-line computer algorithm that was applied to a multilayer radiative transfer problem. Initial measurements were made to specify the spectral windows for traceable compounds, to test the sensitivity of the system, and to develop calibration and continuum handling procedures. To obtain information about the radial temperature and concentration profiles, we developed an algorithm for the analysis of an axial-symmetric multilayered plume by use of the CO2 hot band at approximately 2400 cm(-1). Measurements were made with several in-service engines. Effects that were due to engine aging were detected but have to be analyzed systematically in the near future. Validation measurements were carried out with a conventional propane gas burner to compare the results with those obtained with standard measurement equipment. These measurements showed good agreement to within +/- 20 per cent for the CO and NOx results. The overall accuracy of the system was found to be +/- 30 per cent. The detection limits of the system for a typical engine plume (380 deg C, phi = 50 cm) are below 0.1 per cent for CO2 about 0.7 per cent for H2O, about 20 ppmv (parts per million by volume) for CO, and about 90 ppmv for NO.