Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Hydrogen (mass %) 13.4-14.1 n/a (Report)a 90.4
Sulfur (mass %) < 0.3 a 0.30 a 0.30 100
Viscosity at -20°C (mm 2 s -1 ) 2.5-6.5 a 8.0 a 8.0 100
a) Aromatics a 25% allowed if hydrogen content is reported
b) Smoke point b 19mm allowed if naphthalenes < 3.0%.
Several methods based on the above principles have been developed and are undergoing continuing improvements. The key element of these simplified methods is
the assumption that emission indices at different engine inlet conditions might be correctable to a reference day condition, thus collapsing into a single function of the
corrected fuel flow (Lecht and Deidewig, 1994; Martin et al., 1994, 1995; Deidewig et al., 1996). An example of the effectiveness of such a method developed for NOx emissions is outlined in Figures 7-31 and 7-32. Figure 7-31 shows actual NOx emission indices according to ambient flight conditions and calculated with a complex
correlation formula; Figure 7-32 gives the result of the same values but corrected for ISA SLS conditions. For comparison, ICAO LTO cycle test data are marked
separately.
This method allows ISA SLS measurements to act as a reference function; this function simply has to be re-corrected for actual in-flight engine inlet conditions. These
simplified emission correlation methods are highly relevant in terms of their value for the further development of aircraft emission inventories (see Chapter 9). There is,
as yet, no fuel flow-based correlation that can be used to predict engine soot for the purposes of inventory preparation because of the use of SN data in the ICAO
emissions databank, which cannot readily be converted to soot loading (Döpelheuer and Lecht, 1999).
7.7.3. Validation of Emission Prediction Methods
7.7.3.1. Altitude Chamber Testing
Cruise-level emission index prediction methods need validation by measurement. Such validation can be carried out at ground-level test chambers in which pressure
and temperature can be varied to simulate a wide range of engine operation conditions in flight. Within the AERONO x project, exhaust emissions of two selected
engines (Rolls Royce RB211 and Pratt & Whitney PW305) have been analyzed and compared with predictions (Lister et al., 1995). This comparison shows that
emission prediction methods developed by engine manufacturers and research institutes can predict the NO x emission at a flight condition within an error band of 5-
10% for a modern high bypass engine. These experiments found a tolerance for fuel-based methods that was nearly as good. Measurements from the AERONOx project also showed that for highest accuracy, the prediction equations must be adapted for specific engine type. A kind of indirect validation has been undertaken by
comparing NOx emissions of fuel flow-based methods with the p3 /T3 method. Such an evaluation showed an agreement within 13% maximum and 6% standard
deviation for a variety of aircraft and flight missions (ICAO, 1995c).
7.7.3.2. Validation by In-Flight Measurement
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