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The chemical properties of the particulate exhaust emissions from an in-use commercial aircraft engine were characterized in April 2004 as part of the Aircraft Particle Emissions Experiment. The test aircraft was the NASA DC-8 equipped with CFM56-2-C1 engines and the test matrix included 11 different engine throttle levels, three fuel compositions, and three sampling distances. The variations in particle emissions number, size, mass, and chemical composition were measured using a suite of instruments, including an aerosol mass spectrometer. The particle emissions were characterized by a trimodal size distribution. The largest mode was dominated by ambient accumulation mode particles mixed into the plume. The middle mode consisted of carbon soot with sulfate and organic coatings. The smallest mode was completely volatile and consisted of sulfate and organic components. The soot emission indices increased with power from 2―120 mg/kg fuel. The semivolatile components increased with distance and decreased with power from 33―5 mg/kg fuel. The sulfate emissions increased with distance and fuel sulfur content. The emissions under low power were dominated by organics, and the high-power conditions were dominated by soot. The CFM56 engine was less efficient at the low thrust levels typically used on the ground at an airport.

A proton transfer reaction mass spectrometer was used to measure the concentrations of selected volatile organic compounds in the exhaust of a commercial turbofan aircraft engine. Nine different compounds including methanol, acetaldehyde, acetic acid, benzene, toluene, phenol, styrene, naphthalene, and the methylnaphthalenes were identified as engine exhaust components that are free of spectral interferences and quantifiable by the proton transfer reaction mass spectrometer. The emission characteristics of the engine were examined as a function of engine power, fuel composition, and downstream distance from the engine. The hydrocarbon emission indices were found to be highly variable, upwards to a factor of 10 for the same nominal engine power setting. Although the magnitude of the HC emissions exhibited large variation, we observed that plots of the HC emission indices versus that of the emission index determined for formaldehyde (normalized plots) were linear and essentially independent of power setting and fuel composition, which suggests that the HC emissions scale together. The results of this study are critically examined and are shown to compare favorably with those of previous studies and serve to validate the proton transfer reaction mass spectrometer method as a reliable quantitative technique for online monitoring of selected hydrocarbon emissions within the engine exhaust matrix.

and10-m sampling rakes contained multiple gasandparticle inlet probes to facilitate astudy of the spatial variation of emissions across the engine exhaust plane. Gas-phase emission indices measured at 1 m were in good agreement withtheenginecertificationdataaswellaswithpredictionsprovidedbytheenginecompany.However,atlowpower settings, trace-species emissions were observed to be highly dependent on ambient conditions and engine temperature. Nonvolatile particles emitted by the engine exhibited a log-normal size distribution that peaked between 15 and 40 nm, depending on engine power. Samples collected 30 m downstream of the engine exit plane exhibited a prominent nucleation mode, indicating that secondary aerosols composed of sulfuric acid and low- volatility organic species formed rapidly within the plume as it expanded and cooled. Black carbon emissions were a minimum at approach and a maximum at climb and takeoff engine power settings. Black carbon dominated total mass emissions at high thrust, whereas volatile particles contributed an equal or perhaps greater fraction at low- to midpower settings. Although variations in fuel aromatic content had no discernible impact on particle emissions, volatile particle number and mass concentrations in aged exhaust plumes were highly sensitive to the fuel sulfur content.