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Figure III-3. Formaldehyde emission index
versus fuel flow.
EI HC column are the UHC emission indices at idle thrust
setting (7% thrust). The black entries labeled with black arrows
are from combustors with similar characteristics. When the
entry with the highest fuel flow/lowest emission index is Figure III-4. ICAO emissions performance databank
used to normalize each entry, we can compare the relationship analysis. The upper table shows selected columns
of the UHC emissions index with absolute fuel flow for the and rows from the ICAO emissions performance
CFM56-7Bxx family of engines to the data collected in the databank. The inset graph depicts the results of an
tests conducted for this project. analysis scheme that addresses the relative UHC
Essentially, the exercise described in Figure III-4 uses the emission index increase caused by small changes in
ICAO databank to form a generalized UHC dependence on fuel flow for idling engine operation.
fuel flow at near-idle condition. This procedure will be used
to account for the engine-to-engine variability observed in
absolute UHC emission indices for the on-wing engine tests
The unnormalized data is depicted in Appendix A as
in order to draw out whatever trend may exist in the UHC
Figure A01-E12b, and the three apparent ratios of the emission
emission index with fuel flow. This procedure is also used to
index (at a given fuel flow rate) relative to the measured
directly examine any systematic coupling between fuel flow
emission index at the N1 = 25% fuel flow are tabulated in the
and specific VOC emission indices.
legend. The uncertainties in the slopes are twice the standard
The construct described in Figure III-4 is referred to in this
error of the fitting procedure. This process can be extended to
document as the near-idle fuel flow dependence. Formally,
the entire dataset for all engines and all VOC species.
the slope of this assumed line carries units of s kg-1, and is the
slope parameter in the following expression.
III.3Ensemble Result for
HC ( Fuel Flow ) s Fuel Flow Dependence
= 1 + slope [ Fuel Flow - FF7% ]
HC ( FF7% ) kg The entire dataset has been analyzed for each VOC follow-
ing the procedure described in the preparation of Figures III-4
In this case the fuel flow is the independent variable, and and III-5. The histogram of all these results has been plotted
the result is effectively a multiplicative factor that can project in Figure III-6. This result forms the basis of the fuel flow
the UHC emission index to fuel flows lower than the fuel flow dependence that will be carried forward to a near-idle emis-
at 7% thrust (FF7%) in the expression above. sions index model described later. The goal of this project
is to quantify HAP emissions from idling aircraft as a function
of engine and ambient conditions. Despite the complexities of
III.2 Test Results for Engine SA012
working with on-wing engines and the various bleed air
The test results for the aircraft engine "SA012" in Appendix A operational states, the result depicted in Figure III-6 sug-
are plotted in Figure III-5 using the normalization procedure gests an increase in the VOC emissions index with reduced
described in Figure III-4. fuel flow. The histogram for all the VOC project data fit to a
