Article pubs.acs.org/EF
Influence of Jet Fuel Composition on Aircraft Engine Emissions: A Synthesis of Aerosol Emissions Data from the NASA APEX, AAFEX, and ACCESS Missions Richard H. Moore,*,† Michael Shook,†,‡ Andreas Beyersdorf,† Chelsea Corr,¶,† Scott Herndon,§ W. Berk Knighton,∥ Richard Miake-Lye,§ K. Lee Thornhill,†,‡ Edward L. Winstead,†,‡ Zhenhong Yu,§ Luke D. Ziemba,† and Bruce E. Anderson† †
NASA Langley Research Center, Hampton, Virginia 23681, United States Science Systems and Applications, Inc. (SSAI), Hampton, Virginia 23666, United States ¶ NASA Postdoctoral Program, Oak Ridge Associated Universities, Oak Ridge, Tennessee 37830, United States § Aerodyne Research, Inc., Billerica, Massachusetts 01821, United States ∥ Montana State University, Bozeman, Montana 59717, United States ‡
S Supporting Information *
ABSTRACT: We statistically analyze the impact of jet fuel properties on aerosols emitted by the NASA Douglas DC-8 (Tail No. N817NA) CFM56-2-C1 engines burning 15 different aviation fuels. Data were collected for this single engine type during four different, comprehensive ground tests conducted over the past decade, which allow us to clearly link changes in aerosol emissions to fuel compositional changes. It is found that the fuel aromatic and sulfur content most affect the volatile aerosol fraction, which dominates the variability (but not necessarily the magnitude) of the number and volume emissions indices (EIs) over all engine powers. Meanwhile, the naphthalenic content of the fuel determines the magnitude of the nonvolatile number and volume EI as well as the black carbon mass EI. Linear regression coefficients are reported for each aerosol EI in terms of these properties, engine fuel flow rate, and ambient temperature and show that reducing both fuel sulfur content and naphthalenes to near-zero levels would result in roughly a 10-fold decrease in aerosol number emitted per kilogram of fuel burned. This work informs future efforts to model aircraft emissions changes as the aviation fleet gradually begins to transition toward low-aromatic, low-sulfur alternative jet fuels from biobased or Fischer−Tropsch production pathways.
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INTRODUCTION In-service commercial aircraft emit substantial amounts of aerosol particles that can degrade local air quality and human health near airports, as well as impact Earth’s climate through direct aerosol radiative absorption, contributing cloud condensation nuclei, or modification of the extent and properties of cirrus clouds high in the troposphere. Understanding these impacts is important for assessing the effects of aviation on air quality and climate. In addition, it is important to understand how future changes in the aircraft fleet translate into changes in emissions. Such fleet changes are likely to be brought about by increasing fuel prices, supply security, environmental footprint, and future regulatory pressures.1 For example, the International Air Transport Association (IATA) and Advisory Council for Aviation Research and Innovation in Europe (ACARE) have defined ambitious sector targets, including carbon-neutral growth beginning in 2020 and an overall 50−75% reduction in carbon emissions by 2050 as compared to 2000−2005.2,3 Meeting these challenges will require significant technological advances over the next few decades; however, in the near term, air traffic management and alternative fuels are attractive approaches. Toward this end, the European Union has unveiled a plan to speed up the commercialization of aviation biofuels in Europe.4 These biofuels, along with other alternative fuels synthesized via the Fischer−Tropsch process, are characterized © 2015 American Chemical Society
by near-zero levels of sulfur and aromatics, which significantly reduce aircraft engine aerosol emissions.5−11 Early engine emissions smoke number measurements implicated fuel aromatics as a driver of soot production,12 and more recent work with a T63 helicopter engine further suggests the naphthalenic subset of aromatic species may be particularly important.8 Yet, establishing a quantitative link between these fuel property changes and emissions reductions over the full range of fuel aromatic and sulfur contents remains elusive, in part due to a paucity of quantitative particle emission indices spanning the range of low-sulfur fuel contents (
