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10 Figure III-3 presents all measured formaldehyde emission indices, from every test conducted when the ambient air was lower than 0°C in 2009 and 2010 at MDW, plotted versus fuel flow for 11 different CFM56-7B24 combustors. Of all param- eters recorded in the digital flight data records, fuel flow best linearizes the trend in emission index. Similar patterns are observed in the other specific hydrocarbon measurements, including ethene, acetylene, and 1,3-butadiene. III.1Dependence of VOC on Fuel Flow Near Idle The ICAO engine certification databank (ICAO 2006) defines the idle condition as 7% of rated thrust. An ICAO engine entry specifies the engine combustor and the thrust rating for each particular model certified for use on commer- cial aircraft. In some cases, the combustor technology is not drastically different for entries in the databank with different Figure III-1. Fuel flows resulting from the named thrust ratings. Because the ICAO definition of idle is relative engine condition in the near-idle test matrix to maximum thrust, if the engines using the same combustor (GI = ground idle). These tests were conducted at designs can be identified there may be preexisting data that ambient temperatures between 265K and 271K. can address the dependence of VOC emissions on fuel flow for near-idle operations (DuBois and Paynter 2006). emission indices for several VOC species are actually more Examination of the tabulated total UHC emission indices precise than the capability to reproduce low-fuel-flow engine should provide a qualitative guide for the UHC emissions- states. Although some important differences in the VOC related performance to compare with the trend observed in profile have been uncovered in this study, the same trend Figure III-3. will generally be present in other HAP species when data for Figure III-4 shows a selected portion of the ICAO emissions a particular HAP or VOC are evaluated. databank for total hydrocarbons. The blue data entries in the Figure III-2. N1 fan speed versus fuel flow rate. The data points are colored by exhaust gas temperature. The small data points are the warm-up test points. The data circled in blue represent points where de-icing technologies were enabled.