Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Aviation and the Global Atmosphere
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7.6.4.3. Oxidation Products of Secondary Combustion Species (HNO 2, HNO 3, SO 3, H 2SO 4, H 2O 2, HNO)
Modeling results (Brown et al., 1996; Lukachko et al., 1998) and, for SO x O, initial measurements
(Arnold et al., 1992, 1994, 1999; Fahey et al., 1995a,b; Miake-Lye et al., 1998) indicate that
significant changes in the levels of these species are possible as their source gases are
oxidized. These changes can be important with respect to atmospheric impact (see Chapters 2
and 3). However, most of the important chemical and fluid-mechanical effects remain
unexplored. It is known, however, that strong non-linearities in the chemistry (based on as-yet
unvalidated chemical models) can be accentuated by complex fluid-mechanical effects such as
those associated with viscous boundary layersand wakes and blade cooling (Lukachko et al.,
1998). Figure 7-27 shows an example of this process: Two different modeling results are
compared for a single blade row such as that shown in Figure 7-24. The first modeling result
takes account of spatial temperature nonuniformity associated with blade cooling, whereas the
second is an averaged, one-dimensional representation of the flow path. SO x O oxidation in the
blade row is enhanced when blade cooling is modeled.
Changes in many secondary combustion species from presumably negligible levels after leaving
the combustor cannot yet be predicted with sufficientaccuracy for assessment needs (Dryer et
al., 1993; Miake-Lye et al., 1998). The existing experimental database for these species is
insufficient to validate or improve current model predictions. For example, although models and
initial measurements suggest that significant oxidation of SO 2 to SO 3 occurs within the engine,
the models do not correctly predict the variation in the fraction of sulfur oxidized as fuel sulfur
level is changed-suggesting that an unknown oxidative mechanism may be involved (Schumann
et al., 1996; Danilin et al., 1997; Kärcher and Fahey, 1997; Miake-Lye et al., 1998). Thus, current
understanding is not mature enough to provide accurate initial conditions for aerosol formation
http://www.ipcc.ch/ipccreports/sres/aviation/106.htm (1 von 4)08.05.2008 02:43:41
Figure 7-29: Engine NO x characteristic values of
Dp/Foo for the ICAO LTO cycle, and changes in
regulatory limits.
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