The Atmospheric Effects of Stratospheric Aircraft Project An Interim Review of Science and Progress (1998) / Chapter Skim
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3 Ozone Reduction by HSCT-Emitted Nitrogen Oxides
3 Ozone Reduction by HSCT-Emitted Nitrogen Oxides
Pages 23-35
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From page 23... ...
Although the rate of NOX emission from future HSCT engines is unknown, current estimates for a fleet of 500 Mach 2.4 HSCTs also give NOX injection into the stratosphere at values close to or slightly lower than the natural input noted above. Figure 5, showing calculations by a Lawrence Livermore National Laboratory (LLNL)
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From page 24... ...
It did the pioneering work on stratospheric composition and chemistry, including the first measurements of NO and NO2 in the stratosphere; improved one- and twodimensional atmospheric models; made systematic laboratory measurements of reaction rates applicable to the stratosphere; developed critical tables of chemical rate coefficients and light-absorption cross-sections; and sponsored studies of heterogeneous reactions in the atmosphere and of economic impacts and biological damage caused by ultraviolet radiation (CIAP, 1975a,b)
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From page 25... ...
These calculated ozone reductions were extremely sensitive to flight altitude: For the CIAP value of NOX input, flight altitudes of 15-18 km, 18-21 km, and 21-24 km gave northern hemisphere ozone reductions of 0.9 percent, 10.4 percent, and 13.1 percent, respectively. These three altitude bands correspond approximately to the flight altitudes of aircraft with Mach numbers of 1.6, 2.4, and 3.2, suggesting that aircraft with a low, but still supersonic, Mach number might be able to operate under conditions such that their effect on ozone would be small.
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From page 26... ...
Flight Routes and Fuel Usage With detailed consideration of every major airport in the world and flight paths between pairs of them, realistic HSCT flight routes were identified, flightaltitude patterns for fleets with different Mach numbers were worked out, the economically justified number of HSCTs was tentatively set at 500, and amount of fuel expected to be burned along the various routes was derived. The estimated mass of fuel to be used was 6.6 x 10~° kg per year, of which the fractional consumption is 2.8 percent from 30°S to the south pole, 32.4 percent from 30°S to 30°N, and 64.8 percent from 30°N to the north pole (Prather et al., 1992~.
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From page 27... ...
The Concorde's Olympus engines embody 1960s technology; the engines being developed for the HSCT will have as much as 30 percent greater fuel efficiency. With conventional combustor technology, however, the changed combustor operating conditions that yield these efficiency improvements would result in at least a doubling of the NOX emission index.
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From page 28... ...
10 12 14 FIGURE 6 Projected HSCT fuel consumption in 2015. Top panel: Latitudinal distribution of fuel used above 13 km altitude by a fleet of 500 Mach 2.4 aircraft.
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From page 29... ...
Until such engines have been built and tested, the EI must be considered a large uncertainty in modeling HSCT NOX input into the stratosphere. MODELING HSCT OZONE REDUCTION To represent the three reference points discussed above a new engine based on 1990 technology with no concern for low NOX, the existing Concorde Olympus engine, and the NASA goal for perhaps the year 2001 AESA modelers used 45, 15, and 5 as EI(NOX)
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From page 30... ...
30 · - ~ 3 Vet o in, o o Cal o o Vat a' ~ 3 ¢ a' be .
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From page 32... ...
Those results are condensed here to give an average ozone-column percentage change plus or minus two standard deviations: Mach\EI(NOx) 45 15 3.2 -3.4 + 2.5 -1.1 + 1.2 2.4 -4.4+3.9 -0.69+0.75 -0.19+0.38 1.6 +0.27 + 0.76 +0.19 + 0.50 The calculated ozone reductions in the models that included heterogeneous reactions (Part B of Table 1)
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From page 33... ...
ozone changes for 500 Mach 2.4 HSCTs as a function of NOX emission index for values of 0, 5, 10, and 15 as calculated by five 2-D assessment models. In general, the five models agree that there will be less than 1 percent ozone reduction for any NOX emission index up to 15.
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From page 34... ...
In recent years AESA has restricted its model calculations to HSCTs with Mach number 2.4 and its NOx emission indices to 5 and 15. During the model-development stage, it saves
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From page 35... ...
if AESA modelers included in their calculations of ozone change Mach numbers 1.6 and 3.2, NOx emission indices of O and 45, and a wider range of sulfate number densities in the wake. This expansion would show the context within which the chosen model of HSCT lies, and make sure that no nearby opportunity or possible hazard will be missed.
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