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Power-dependent speciation of volatile organic compounds in aircraft exhaust
Abstract As part of the third NASA Aircraft Particle Emissions Experiment (APEX-3, November 2005), whole air samples were collected to determine the emission rates of volatile organic compounds (VOCs) from aircraft equipped with three different gas-turbine engines (an Allison Engine 3007-A1E, a Pratt–Whitney 4158, and a Rolls–Royce RB211-535E4B). Samples were collected 1 m behind the engine exhaust plane of the engines while they were operated at powers ranging from idle up to 30% of maximum rated thrust. Exhaust emission indices (mass emitted per kilogram of fuel used) for CO and non-methane hydrocarbons (NMHCs) were calculated based on enhancements over background relative to CO2. Emissions of all NMHCs were greatest at low power with values decreasing by an order of magnitude with increasing power. Previous studies have shown that scaling idle hydrocarbon emissions to formaldehyde or ethene (which are typically emitted at a ratio of 1-to-1 at idle) reduces variability amongst engine types. NMHC emissions were found to scale at low power, with alkenes contributing over 50% of measured NMHCs. However, as the power increases hydrocarbon emissions no longer scale to ethene, as the aromatics become the dominant species emitted. This may be due in part to a shift in combustion processes from thermal cracking (producing predominantly alkenes) to production of new molecules (producing proportionally more aromatics) as power increases. The formation of these aromatics is an intermediate step in the production of soot, which also increases with increasing power. The increase in aromatics relative to alkenes additionally results in a decrease in the hydroxyl radical reactivity and ozone formation potential of aircraft exhaust. Samples collected 30 m downwind of the engine were also analyzed for NMHCs and carbonyl compounds (acetone, 2-butanone and C1–C9 aldehydes). Formaldehyde was the predominant carbonyl emitted; however, the ratio of ethene-to-formaldehyde varied between the aircraft, possibly due to the sampling of transient emissions such as engine start-up and power changes. A large portion of the measured emissions (27–42% by mass) in the plume samples was made up of hazardous air pollutants (HAPs) with oxygenated compounds being most significant.
Highlights ► At low power, scaling hydrocarbons to ethene reduces variability amongst engines. ► At high power, there is a difference in composition with aromatics dominating. ► At low power, thermal cracking dominates. ► At high power, aromatic species are formed via the HACA process in the exhaust. ► In downwind samples, HAPs make up a large portion of measured emissions (27–42%).
Power-dependent speciation of volatile organic compounds in aircraft exhaust
Abstract As part of the third NASA Aircraft Particle Emissions Experiment (APEX-3, November 2005), whole air samples were collected to determine the emission rates of volatile organic compounds (VOCs) from aircraft equipped with three different gas-turbine engines (an Allison Engine 3007-A1E, a Pratt–Whitney 4158, and a Rolls–Royce RB211-535E4B). Samples were collected 1 m behind the engine exhaust plane of the engines while they were operated at powers ranging from idle up to 30% of maximum rated thrust. Exhaust emission indices (mass emitted per kilogram of fuel used) for CO and non-methane hydrocarbons (NMHCs) were calculated based on enhancements over background relative to CO2. Emissions of all NMHCs were greatest at low power with values decreasing by an order of magnitude with increasing power. Previous studies have shown that scaling idle hydrocarbon emissions to formaldehyde or ethene (which are typically emitted at a ratio of 1-to-1 at idle) reduces variability amongst engine types. NMHC emissions were found to scale at low power, with alkenes contributing over 50% of measured NMHCs. However, as the power increases hydrocarbon emissions no longer scale to ethene, as the aromatics become the dominant species emitted. This may be due in part to a shift in combustion processes from thermal cracking (producing predominantly alkenes) to production of new molecules (producing proportionally more aromatics) as power increases. The formation of these aromatics is an intermediate step in the production of soot, which also increases with increasing power. The increase in aromatics relative to alkenes additionally results in a decrease in the hydroxyl radical reactivity and ozone formation potential of aircraft exhaust. Samples collected 30 m downwind of the engine were also analyzed for NMHCs and carbonyl compounds (acetone, 2-butanone and C1–C9 aldehydes). Formaldehyde was the predominant carbonyl emitted; however, the ratio of ethene-to-formaldehyde varied between the aircraft, possibly due to the sampling of transient emissions such as engine start-up and power changes. A large portion of the measured emissions (27–42% by mass) in the plume samples was made up of hazardous air pollutants (HAPs) with oxygenated compounds being most significant.
Highlights ► At low power, scaling hydrocarbons to ethene reduces variability amongst engines. ► At high power, there is a difference in composition with aromatics dominating. ► At low power, thermal cracking dominates. ► At high power, aromatic species are formed via the HACA process in the exhaust. ► In downwind samples, HAPs make up a large portion of measured emissions (27–42%).
Power-dependent speciation of volatile organic compounds in aircraft exhaust
Beyersdorf, Andreas J. (author) / Thornhill, K. Lee (author) / Winstead, Edward L. (author) / Ziemba, Luke D. (author) / Blake, Donald R. (author) / Timko, Michael T. (author) / Anderson, Bruce E. (author)
Atmospheric Environment ; 61 ; 275-282
2012-07-12
8 pages
Article (Journal)
Electronic Resource
English
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