Chemical Speciation of Hydrocarbon Emissions from a Commercial Aircraft Engine

In April 2004, the Aerodyne Mobile Laboratory measured trace gas and particle emissions from a CFM56-2C1 high-bypass-ratio turbofan engine used to power the NASA DC-8 aircraft as part of the Aircraft Particle Emissions Experiment (APEX). This article focuses on the measured hydrocarbon species which include formaldehyde, ethylene, acetaldehyde, benzene, toluene, and several higher aromatic species. Formaldehyde and ethylene were measured by tunable-infrared-laser differential absorption spectroscopy, and the other species were measured by proton-transfer reaction mass spectroscopy. Continuous samples were taken at 1,10, and 30 m downstream of the engine-exit plane of the grounded aircraft and analyzed at a frequency of up to 1 Hz. The engine power was scanned from ground-idle up to takeoff power, and three fuel types (a baseline JP-8, a high-aromatic fuel, and a high-sulfur fuel) were investigated. Fuel type and plume age were shown to have only a minor impact on hydrocarbon emissions within the ranges studied in this experiment. However, ambient temperature was shown to have a substantial effect on these emissions. The sum of these speciated measurements agreed favorably with separate measurements of the total hydrocarbon emissions by flame ionization. The fast time response of the speciated measurements revealed interesting variability and transient behavior on a several-second timescale.