NOX EMISSION INDEXES OF SUBSONIC LONG-RANGE JET AIRCRAFT AT CRUISE ALTITUDE - IN-SITU MEASUREMENTS AND PREDICTIONS

In the course of the Commissions of the European Communities project ' 'Pollution From Aircraft Emissions in the North Atlantic Flight Corrid or (POLINAT)'', in situ measurements of NO, NOx, and CO2 volume mixing ratios in the near-field exhaust plumes of seven subsonic long-range jet aircraft have been carried out by using the research aircraft Falc on of the Deutsche Forschungsanstalt fur Luft- und Raumfahrt (DLR). Fo r three additional aircraft, only NO and CO2 were measured. Plume ages of 50 s to 150 s have been covered, with maximum observed exhaust gas enhancements of 319 parts per billion by volume and 51 parts per mill ion by volume for Delta[NOx] and Delta[CO2], respectively, in relation to ambient values. Aircraft cruising altitudes and Mach numbers range d from 9.1 to 11.3 km and from 0.77 to 0.85, respectively. These measu rements are used to derive NOx emission indices for seven of the indiv idual aircraft/engine combinations. The NOx emission indices derived r ange from 12.3 g/kg to 30.4 g/kg. They are compared with predicted emi ssion index values, calculated for the same aircraft engine and the ac tual conditions by using two newly developed fuel flow correlation met hods. The calculated emission indices were mostly within or close to t he error limits of the measured values. On average, the predictions fr om both methods were 12% lower than the measured values, with an obser ved maximum deviation of 25%. The ratio gamma = [NO2]/[NOx] found duri ng the present measurements ranged from 0.05 to 0.11 for five daytime cases and was around 0.22 for two nighttime cases. BL use of a simple box model of the plume chemistry and dilution these data were used to estimate the initial value gamma(0) present at the engine exit plane. We found gamma(0) values between 0 and 0.15. These were applied to est imate the corresponding NO2 for the three cases in which only NO was m easured.