Remote sensing and analysis of trace gases from hot aircraft engine plumes using FTIR-emission-spectroscopy

To evaluate the influence of air traffic on the upper and lower troposphere, one must find an effective remote sensing method to measure the actual gas emissions of aircraft engines at defined thrust levels at all altitudes. FTIR-Emission-Spectroscopy seems to fulfill these needs by detecting the thermal radiation of the hot exhaust gases, yielding all information about their compounds during one measurement. Several ground-based engine types at different thrust levels have been analysed; e.g. old engines, JT8- and modern CFM56-bypass engines. The IR features have been used to determine the gas temperature and the total number of H2O, CO2, CO, and NO molecules behind the nozzle at different thrust levels. Formaldehyde and other hydrocarbon species have been identified but could not yet be quantified. With respect to the axial temperature distribution, a multi-layer model is used to calculate the radiative transfer through the downstream slices of the cooling plume. Knowing the plume diameter, the fuel consumption and the mass flow of gas at the exit, one can obtain the emission rates and indices for different thrust levels. Once fully developed for passive ground measurements, the system can easily work under flight conditions. Apart from future applications for the turbine development and the engine-status control after a certain flight time, this remote sensing system can deliver emission data from aircraft at all altitudes.