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21 CHAPTER 5 Individual Reviews of Data from the Aircraft Field Measurement Campaigns 5.1 APEX1 The number-based emission index at low thrust levels was found to decrease during the first couple of hours of engine The emissions of a CFM56-2C1 engine burning a range of on time. Number-based emission index similarly decreased fuels (base, high aromatic, high sulfur) were measured during as the ambient air temperature increased. the APEX1 campaign. The PM parameters measured at APEX1 The mass-based emission index increased with thrust, were particle size distributions and emission indices for parti- ranging from <20 mg/kg of fuel burned at idle through cle number and mass (i.e., the number or mass, respectively, of cruise thrust levels and rising to >200 mg/kg of fuel burned particles produced per kilogram of fuel burned), including at takeoff. their volatile and non-volatile fractions. Emission indices were also measured for major combustion gases (carbon dioxide Samples collected downstream of the exhaust nozzle often [CO2], carbon monoxide [CO], nitrogen oxides [NOx], total contained large numbers of volatile particles that contain unburned hydrocarbons [UHC]) and trace combustion gases materials that are gases at temperatures above 300C (572F). (specifically, sulfur dioxide [SO2], nitrous oxide [N2O], nitrous These volatile particles were not observed at the exhaust acid [HONO], and a number of volatile HC). All of the data nozzle but were readily apparent downstream (~30 m [98 ft]). recorded in the APEX1 database were acquired when the engine They evolve as the plume expands and mixes with the ambient was declared to be stable for a given operating condition. air. In terms of volatile particles, the following conclusions The PM in an engine exhaust plume was found to vary in were drawn from APEX1: composition and physical and chemical properties as the plume ages, and the total PM detected had volatile and non- Their number mean diameter ranged from smaller than volatile (black carbon) components depending on the sampling 3 nm to 10 nm. location in the plume. In terms of non-volatile particle emis- At downstream sampling locations, the number-based sions, the following conclusions were drawn from APEX1: volatile particle emission index was typically much higher than that of the black carbon and depended on Non-volatile particles ranged in diameter from smaller fuel composition, thrust level, plume age, and ambient than 10 to 300 nm (i.e. 0.01 to 0.3 m); see Figure 1 for size temperature. comparisons. Compositional analysis of these volatile particles revealed The number mean diameter of the particles increased with that sulfur and HC species accounted for a significant thrust ranging from ~15 nm at idle to ~40 nm at take off fraction of the volatile mass, consistent with condensa- For the three fuels tested, the non-volatile PM parameters tion and nucleation of sulfuric acid/sulfate and HC in the did not vary. cooling plume. Non-volatile PM parameters did not depend on plume age (sampling distance downstream of the exhaust nozzle), in- In the case of the total PM, where no distinction is made dicating that the black carbon component of the exhaust between the volatile and non-volatile components, the fol- does not change as the plume ages. lowing characteristics were observed: The number-based emission index was highest at takeoff thrust, with a smaller peak at idle thrust, and revealed a At high thrust levels, particle mass emissions were domi- minimum at thrust levels corresponding to approach. nated by black carbon at all sampling locations in the plume.