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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 300°C (572°F).
(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.
