Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
An alternate suitable method is to carry out measurements in the freshly emitted exhaust plume
of an aircraft in flight. Several such cruise altitude emissions measurement programs have been
conducted. Cruise altitude in situ chemical probing was carried out for the first time in December
1991, when the DLR research aircraft "Falcon" flew through the plume of a commercial DC-8
airliner (Arnold et al., 1992). In 1993, the first in-flight measurements of emission indices were
accomplished, again using the "Falcon" (Schulte and Schlager, 1996). This measurement
involved measuring CO 2 simultaneously with other species of interest (in terms of volume mixing
ratios). A detailed discussion of these assumptions and the emission index determination from
the measured ratios D[X]/D[CO 2 ] appears in Schulte and Schlager (1996).
In recent years, several in situ EI measurements have been carried out. Fahey et al. (1995a,b)
determined emission indices for NO x , CO, and N 2 O in the exhaust plumes of the NASA ER-2
research aircraft and the Concorde in the lower stratosphere. Haschberger and Lindermeir
(1996, 1997) analyzed the exhaust plume of the DLR experimental Advanced Technology
Testing Aircraft System of DLR, a two-engine jet aircraft of type VFW 614 (ATTAS) with onboard
instruments and derived emission indices for NO x , CO, and H 2 O. The subsonic long-range jet
aircraft types that dominate global air traffic were investigated by Schulte et al. (1997) to derive
NO x emission indices. Figure 7-33 shows a comparison of all available in situ measured EI(NO x )
values with corresponding predicted values. Note that the measurement details were different for
each case.
In summary, these measurements revealed good agreement between predicted and measured
NO x emission indices. Special attention was paid to predictions based on fuel flow methods
(Lecht and Deidewig, 1994; Deidewig et al., 1996; Martin et al., 1996; Schulte and Schlager,
1996; Schulte et al., 1997) because they are the methods of choice for the building of aircraft
NO x emission inventories. These methods seem to underestimate EI(NO x ) by about 12% on
average. However, this 12% deviation is within the uncertainties-indicated as error bars-of the
measurements and the predictions.
7.7.4. Engine Emission Variations
Engine emissions may vary for a number of reasons. Manufacturing differences, aging
characteristics for individual engines, operational and atmospheric conditions, and changes in
fuel contents all have parts to play. Data from new engine certification testing reveals a standard
deviation for EI(NO x ) of 1-7%. Fuel type, fuel content, and sampling methods have only a slight
influence on NO x emission variation (Lyon et al., 1980; Lukachko and Waitz, 1997). Another
major source of variability may be engine deterioration over a long period of time. This
deterioration is evident in measurements of engine parameters such as exhaust gas
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Figure 7-34: 1996 UK survey of hydrogen content in
jet fuel.
Figure 7-35: 1996 UK survey of sulfur content in jet
fuel.