Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Secondary products (e.g., NO, NO 2 , N 2 O, SO 2 , CO, stable HC) NO x is little changed by flow through turbine. Oxidation of NO and NO 2 to HONO
Oxidation products of secondary combustion species (e.g.,
HNO 2 , HNO 3 , SO 3 , H 2 SO 4 , H 2 O 2 , HNO)
and HNO 3 , occurring mainly in the high-pressure turbine, is a few percent or less.
For civil engines, CO and HC are relatively unchanged in the turbine, but
significant reductions can occur there in advanced military engines. Accurate NOx predictions and measurements are now routinely performed for assessment
purposes.
Chemical mechanisms and reaction rates of trace species are not well known
over the range of post-combustor conditions. The impact of fluid mechanics on
chemical evolution is not yet fully evaluated by models or measurements.
Reactive species (e.g., O, OH, HO 2 , SO, H 2 , H, N, CH) As above, but validation of trace species chemistry mechanisms, via
measurements, is also needed over the relevant temperature and pressure range
for both classes. Further modeling is required to make the connection with
species for which measurements are not available.
7.6.4.1. Primary Exhaust Constituents (H 2O, CO 2, N 2O 2)
Apart from the small effect of reactions involving trace species, changes in major species concentration in the turbine and nozzle flow path are caused by the diluting
effect of cooling air. CO 2 changes less than a few tenths of a percent as a result of oxidation of CO (increases in H 2 O from HO x recombination are even smaller). This
CO 2 fractional increase may grow in the first stages of the high-pressure turbine as more advanced cycles are implemented because associated cycle changes may
result in relatively more CO at the entrance to the turbine (Godin et al., 1995, 1997; Leide and Stouffs, 1996). Current small changes and likely future changes in
primary exhaust constituents can be predicted with sufficient accuracy (Dryer et al., 1993) for assessment needs, however, and the levels are all relatively easy to
derive from measurements.
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