Experimental Test of the Influence of Propulsion Efficiency on Contrail Formation

Abstract

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.

Contrail Modeling and Simulation

“…The Schmidt-Appleman criterion has been validated by in situ measurements (Busen & Schumann 1995, Petzold et al 1997, Jensen et al 1998b) and numerical simulations (Paoli et al 2004(Paoli et al , 2013. Interestingly, Equation 2 implies that modern aircraft that have higher propulsion efficiency (and therefore cooler exhausts) may form contrails at ambient higher temperatures over a larger range of cruise altitudes, as nicely shown in experiments by Schumann et al (2000).…”

Ice supersaturation and the potential for contrail formation in a changing climate

“…Lee et al, 2009), many studies have considered possible strategies to reduce contrail formation in the future, for example by developments to engine technology Haglind, 2008) or by changing aircraft altitude (Williams et al, 2002;Fichter et al, 2005;Mannstein et al, 2005;Rädel and Shine, 2008;Schumann et al, 2011;Deuber et al, 2013) or route (Sridhar et al, 2013;Irvine et al, 2014b;Soler et al, 2014;Zou et al, 2015) to avoid flying through ISS regions. In addition, it is likely that contrail formation will become more frequent due to increased air traffic, and the introduction of newer, more efficient engines, which consume less fuel but allow contrail formation to occur at higher temperatures and thus over a wider range of cruise altitudes than at present (Schumann, 2000;Schumann et al, 2000;Marquart et al, 2003). Using projected future air traffic scenarios, including an increase in engine propulsion efficiency, but with a present-day climate, Gierens et al (1999) projected that global-mean contrail cover would increase by a factor of between 3 and 9 by 2050 (depending on the scenario used) relative to 1992.…”

Aircraft type influence on contrail properties

“…The altitude range where contrails form is mainly controlled by ambient temperature and humidity and by aircraft fuel properties (water vapour emission index and specific combustion heat) (Schumann, 1996), with a weak influence of the overall propulsion efficiency of the aircraft-engine combination (Schumann, 2000;Schumann et al, 2000). At the high relative humidity during contrail formation, the engine exhaust plume contains an aerosol of non-volatile (mainly soot) and volatile particles from condensing particle precursors (sulphuric acid, organic acids) and part of this aerosol gets activated and liquid droplets form which then freeze and form ice particles (Kärcher and Yu, 2009).…”