Abstract:The WeCare project (Utilizing Weather information for Climate efficient and eco efficient future aviation), an internal project of the German Aerospace Center (Deutsches Zentrum für Luft-und Raumfahrt, DLR), aimed at finding solutions for reducing the climate impact of aviation based on an improved understanding of the atmospheric impact from aviation by making use of measurements and modeling approaches. WeCare made some important contributions to advance the scientific understanding in the area of atmospheric and air transportation research. We characterize contrail properties, show that the aircraft type significantly influences these properties, and how contrail-cirrus interacts with natural cirrus. Aviation NO x emissions lead to ozone formation and we show that the strength of the ozone enhancement varies, depending on where within a weather pattern NO x is emitted. These results, in combination with results on the effects of aerosol emissions on low cloud properties, give a revised view on the total radiative forcing of aviation. The assessment of a fleet of strut-braced wing aircraft with an open rotor is investigated and reveals the potential to significantly reduce the climate impact. Intermediate stop operations have the potential to significantly reduce fuel consumption. However, we find that, if only optimized for fuel use, they will have an increased climate impact, since non-CO 2 effects compensate the reduced warming from CO 2 savings. Avoiding climate sensitive regions has a large potential in reducing climate impact at relatively low costs. Taking advantage of a full 3D optimization has a much better eco-efficiency than lateral re-routings, only. The implementation of such operational measures requires many more considerations. Non-CO 2 aviation effects are not considered in international agreements. We showed that climate-optimal routing could be achieved, if market-based measures were in place, which include these non-CO 2 effects. An alternative measure to foster climate-optimal routing is the closing of air spaces, which are very climate-sensitive. Although less effective than an unconstrained optimization with respect to climate, it still has a significant potential to reduce the climate impact of aviation. By combining atmospheric and air transportation research, we assess climate mitigation measures, aiming at providing information to aviation stakeholders and policy-makers to make aviation more climate compatible.

The increasing environmental requirements in the air transport sector pose great challenges to the aviation industry and are key drivers for innovation. Besides various approaches for increasing the efficiency of conventional gas turbine engines, electric propulsion systems have moved into the focus of aviation research. The first electric concepts are already in service in general aviation. This study analyses the potentials of electric and turbo hybrid propulsion systems for commercial aviation. Its purpose is to compare various architectures of electrical powertrains with a conventional turboprop on a regional aircraft, similar to the ATR 72, on engine and flight mission levels. The considered architectures include a turbo-electric (power controlled and direct driven), hybrid-electric (serial and parallel) and a pure electric concept. Their system weights are determined using today’s technology assumptions. With the help of performance models and flight mission calculations the impact on fuel consumption, CO ${}_{2}$ emissions and aircraft performance is evaluated.

According to a previously established thermodynamic theory, contrails are expected to form at a threshold temperature that increases with the overall ef ciency of the aircraft propulsion. As a consequence, aircraft with modern engines, with higher overall ef ciency, cause contrails over a larger range of cruise altitudes. To validate this theory, an experiment was performed in which contrail formation was observed behind two different fourengine jet aircraft with different engines ying wing by wing. Photographs document the existence of an altitude range in which the aircraft with high engine ef ciency causes contrails whereas the other aircraft with lower engine ef ciency causes none. For overall ef ciencies of 0.23 and 0.31 and an ambient temperature lapse rate of 12 K km ¡ 1 , the observed altitude difference is 80 m. This value would be larger (200 m) in a standard atmosphere with smaller temperature lapse rate (6.5 K km ¡ 1 ). In a standard atmosphere, an increase of overall ef ciency from 0.3 to 0.5, which may be reached for future aircraft, would cause contrails at about 700 m lower altitude.

Abstract. Emission indices were derived from in-flight measurements of CO, nonmethane hydrocarbons (NMHCs), H20 , and nonvolatile condensation nuclei in the exhaust plumes of the Deutsches Zentrum far Luft-und Raumfahrt VFW 614 (ATTAS) and NASA DC-8 experimental aircraft. CO emission indices, EIs(CO), of the ATTAS Rolls Royce M 45H Mk501 engines were determined concurrently by two independent techniques: monitoring of exhaust emissions using a customized Fourier transform infrared spectrometer (FTIR) and by simultaneous continuous fast CO and CO2 measurements. The EIs(CO) determined by FTIR were systematically 28% lower than those derived from the CO/CO2 concentration ratios. The EIs(CO) of the newer and larger CFM 56-2C1 engines, used on DC-8, were substantially smaller than those of the ATTAS engines. The emission behavior of CFM 56-2C1 engines is very similar to CFM 56-3 engines frequently used on Boeing 737 aircraft. In-flight derived EIs(CO) of the ATTAS engines were strongly dependent on the fuel flow rate and agreed well with those calculated from ground-based measurements. Emission indices for individual NMHCs were determined from the concentration ratios of NMHC/CO in the plume of ATTAS and DC-8 and from the EIs(CO) determined by FTIR or derived from the concentration ratios of CO/CO2. The EIs(NMHC) are highest for alkenes and alkynes generated by a cracking of larger fuel molecules and for benzene from unburnt fuel, and they depend strongly on the power setting of the engines. As with EIs(CO), the EIs(NMHC) of the CFM 56-2C1 engine tend to be smaller than those of the Rolls Royce M 45H Mk501.

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