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28 Appendix A Project Results Introduction Sampling and Analysis Methodology Staged tests were performed with both a stationary one-meter Figure A01-1 depicts a schematic of the methodology used probe or by using the Aerodyne Mobile Laboratory as a mobile to sample engine emissions during the MDW 2009 quick look probe driving through the exhaust plume with a prevailing study. In this approach, the aircraft engine is not operated above headwind. Staged tests performed at DAL 2009 and MDW N1 = 25% (CFM56-7B24), which ensures that the engine thrust 2010 provided an opportunity to test with a one-meter does not damage the mobile laboratory in the thrust wake. probe placed directly behind and engine operating at various The air mass, sampled continuously, consists of a dynamic ground idle conditions. Tests performed on the taxiways of mixture of core-flow emissions mixed with an unknown all three airports visited under this project allowed measure- and dynamically varying dilution fraction. The measurement ments of exhaust plumes after natural dilution. In these latter as a function of time can be described by the following measurements specific information on the engine operating equation. conditions is not known, however this constitutes a dataset comprised of a multitude of different engines sampled while [ X ]measured = f [ X ]post-combustion-core-emission + (1 - f ) [ X ]ambient in-use. The testing from DAL 2009 can be compared to testing (A-1) at MDW and ORD to get comparison of emissions at dif- ferent ambient temperatures. DAL 2009 was conducted with The method used to distinguish the core-flow plume warm ambient temperatures (24C) while MDW and ORD constituents from the ambient is based on time series analy- tests were performed during the winter (-5C). The dataset sis (Herndon et al. 2004). The measurement at each of the produced from this project is described in this appendix. continuous instruments will be a comprised of a mixture of The dataset is available as an excel format spreadsheet. core-flow combustion and ambient mixing ratios. In expression (A-1), f represents the time dependent volume fraction of core flow that is being sampled. The quantity f(t) A01--Staged Aircraft Testing is modulated by the engine by-pass flow turbulently mixing from the MDW 2009 Mission with the atmospheric shear field. Should f(t) be zero for an The testing conducted during the MDW 2009 mission entire sampling period, there will be no capacity to estimate involved staging four Boeing 737 aircraft on two separate [X]post-combustion-core-emission with the dataset. early mornings where the weather forecast called for cool To illustrate how (A-1) has been used to deduce precipitation free conditions. A single 737-300 and three [X]post-combustion-core-emission the time series for multiple measured 737-700 were tested. The 737-700 aircraft were equipped with quantities are used. The apparent baseline magnitudes for a digital flight data record system that specified the engine state each of these species are equivalent to the ambient values during the test. The 737-700 aircraft tested were equipped with measured when the mobile lab is outside of the engine flow CFM56-7B22 engines that had been upgraded via software to (e.g., upwind of the aircraft) or when a crosswind compo- perform as a CFM56-7B24 engine type. nent is pushing the engine core flow away from the sample location. This section of the Appendix will briefly discuss the sam- Using equation (A-1) for compounds such as those in pling and analysis method before discussing the results of Figure A01-2, it can be shown that for a time series contain- the MDW 2009 measurement campaign. ing time periods from non zero values of f(t) the relationship

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29 Figure A01-1. Sampling Scheme Figure A01-3. Correlation plot of using the mobile laboratory HCHO and CO2 from MDW 2009 inlet as the exhaust probe. testing. between two species, as X in (A-1) in the exhaust can be deter- If the time response of both species a and b is matched in mined by, time and any potential lag between the two measurements accounted for, when the measurement of a is plotted against [a ]post-combustion-core-emission the measurement of b, for a time interval that contains non- [a ]measured - [a ]ambient = - [ a ]ambient =m (A-2) zero f(t) a linear fit of the correlation plot will yield a slope, m, [b ]measured - [b ]ambient [b ]post-combustion-core-emission in (A-2). The slope of the fit of HCHO with respect to CO2 (depicted - [b ]ambient in Figure A01-3) is 0.750.02 with units of ppbv pppm-1 (R2 = 0.98) where the error bar tabulated is twice the standard error of the slope parameter. The slope is related to the desired quantity, the emis- sion ratio of a (depicted in Figure A01-3 as HCHO) to CO2 (labeled b in the formulas) in the post-combustion-exhaust by rearranging without approximation to yield equation (A-3). [a ]post-combustion-core-emission [b ]ambient = m 1 - [b ]post-combustion-core-emission [b ]post-combustion-core-emission + [a ]ambient (A-3) [b ]post-combustion-core-emission In the case of using CO2 to act as the dilution tracer the following limits can be used to estimate the systematic error inherent to this approach by making the reasonable assump- tion that the CO2 in the core flow is 2% (or 20,000 ppmv) and CO2 in the ambient is ~390 ppmv. [a ]post-combustion-core-emission 390 ppmv [a ]ambient = m 1 - + [b ]post-combustion-core-emission 20, 000 ppmv 20, 000 ppmv (A-3a) Figure A01-2. Example time series of CO2, CO, formaldehyde and ethene during The first term in this expression suggests that the error a plume encounter at MDW (2009). introduced by assuming that m is equivalent to the ratio of

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30 the a to CO2 in the core flow is less than 2%. The second term Results from CFM56-7B24 in this expression depends on the magnitude of [a]ambient which MDW 2009, DAL 2010 and is compound specific, however it can be asserted that this MDW 2010 Testing error is much less than 0.01% for CO and the hydrocarbon compounds. The results from the testing conducted where the digital flight data record is available are tabulated and depicted below. An uncorrected application of the methodology of com- The table and figure numbers have been generated based on pound slopes diluted to an unknown extent in the ambient, the engine test in question. The number following the letter E systematically biases calculated emission indices high by denotes which engine index is associated with the test result. 1.7 to 2.1% for aircraft exhaust emissions when the CO2 At the request of the cooperating airline, the associated aircraft core flow is 1.9 to 2.2% by volume and the species being tail number and additional information is available by special studied is present in the ambient at less than 1 ppmv. request only and not part of the public release of this project. Table A01-E1a. Selected test results for engine SA001 (MDW2009), aircraft test conducted from 3/3/09 04:00 to 3/3/09 05:00, ambient temperature 266.91K, relative humidity 71%. Fuel Flow 2 N1 2 CO EI S FID EI 2 -1 -1 -1 -1 -1 kg s kg s % % g kg g kg g kg g kg-1 0.0910 20.900 0.000 78.340 0.800 8.170 0.410 0.0985 0.0007 20.650 0.071 73.955 0.616 8.275 0.502 0.1050 0.0014 25.000 0.141 56.055 0.895 6.030 0.439 Engine SA_001 Fuel Flow 2 C2H4 EI 2 HCHO EI 2 Benzene EI 2 kg s-1 kg s-1 g kg-1 g kg-1 g kg-1 g kg-1 g kg-1 g kg-1 0.0910 2.990 0.010 2.480 0.050 0.270 0.007 0.0985 0.0007 2.450 0.098 2.155 0.055 0.215 0.006 0.1050 0.0014 1.785 0.063 1.630 0.028 0.160 0.006 Engine SA_001 Fuel Flow 2 Toluene EI 2 C2-Benzene 2 Styrene 2 kg s-1 kg s-1 g kg-1 g kg-1 g kg-1 g kg-1 g kg-1 g kg-1 0.091 0.173 0.003 0.166 0.003 0.113 0.003 0.0985 0.0007 0.137 0.004 0.122 0.005 0.102 0.002 0.105 0.0014 0.111 0.002 0.112 0.004 0.087 0.004 Table Notes. The 2 value is computed as twice the standard error of the fit emission ratio converted to emission index. When multiple data points have been averaged at the noted fuel flow rate, these errors have been added in quadrature.

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31 Figure A01-E1b. Emission Index for engine SA001 for CO, HCHO, C2H4, and C6H6. The four figures depict the emission indices in grey with the precision-based error bar from the entire CFM56-7B24 dataset. The colored data points are the emission index for the species in question averaged for the nominal engine state during the test of engine index SA-001. In many cases the precision based error bar for the emission index is smaller in magnitude than the size of the data point. See companion table for precision-based error bars. The absolute averaged emission indices for the fuel flow repeats during the test are depicted in the four panels; upper left CO in black; upper right HCHO in orange; lower left ethene (C2H4) in magenta; and lower right benzene (C6H6) in violet.

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32 Figure A01-E1c. Emission Index for engine SA001 for Toluene, C2-Benzene, Styrene, and Naphthalene. C2-Benzene refers to the sum of the xylene isomers and ethyl-benzene. The four figures depict the emission indices in grey with the precision-based error bar from the entire CFM56-7B24 dataset. The colored data points are the emission index for the species in question averaged for the nominal engine state during the test of engine index SA-001. In many cases the precision based error bar for the emission index is smaller in magnitude than the size of the data point. See companion table for precision-based error bars. The absolute averaged emission indices for the fuel flow repeats during the test are depicted in the four panels; upper left Toluene in red; upper right C2-Benzene in light-blue; lower left Styrene in light green; and lower right naphthalene in the larger grey squares.

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33 Figure A01-E1d. Emission Index for engine SA001 using the continuous FID instrument. The grey data points and error bars are the full FID EI dataset collected during the project, which only includes CFM56-7B24 data at MDW 2009. The larger points, in blue are the results for engine 1. Table A01-E2a. Selected test results for engine SA002 (MDW 2009). Aircraft test conducted from 3/3/09 04:00 to 3/3/09 05:00, ambient temperature 266.91K, relative humidity 71%. Fuel Flow 2 N1 2 CO EI 2 FID EI 2 kg s-1 kg s-1 % % g kg-1 g kg-1 g kg-1 g kg-1 0.0828 0.0004 21.320 0.130 76.0 1 9.7 0.75 0.0910 21.200 0.000 71.25 0.4 9.0 0.29 0.0965 0.0007 23.000 2.970 63.1 4 7.5 0.67 0.1030 26.100 0.000 55.3 1.1 7.5 0.50 Engine SA_001 Fuel Flow 2 C2H4 EI 2 HCHO EI 2 Benzene EI 2 kg s-1 kg s-1 g kg-1 g kg-1 g kg-1 g kg-1 g kg-1 g kg-1 0.0828 0.0004 2.616 0.07 2.21 0.05 0.242 0.007 0.0910 2.190 0.01 1.99 0.03 0.210 0.006 0.0965 0.0007 1.875 0.06 1.70 0.07 0.175 0.006 0.1030 1.570 0.02 1.44 0.05 0.160 0.008 Engine SA_001 Fuel Flow 2 Toluene EI 2 C2-Benzene 2 Styrene 2 kg s-1 kg s-1 g kg-1 g kg-1 g kg-1 g kg-1 g kg-1 g kg-1 0.0828 0.0004 0.158 0.005 0.163 0.007 0.101 0.005 0.0910 0.132 0.002 0.136 0.002 0.088 0.001 0.0965 0.0007 0.112 0.002 0.119 0.010 0.086 0.009 0.1030 0.100 0.003 0.116 0.003 0.083 0.003 Table Notes. The 2 value is computed as twice the standard error of the fit emission ratio converted to emission index. When multiple data points have been averaged at the noted fuel flow rate, these errors have been added in quadrature.

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34 Figure A01-E2b. Emission Index for engine SA002 for CO, HCHO, C2H4, and C6H6. The four figures depict the emission indices in grey with the precision-based error bar from the entire CFM56-7B24 dataset. The colored data points are the emission index for the species in question averaged for the nominal engine state during the test of engine index SA-002. In many cases the precision based error bar for the emission index is smaller in magnitude than the size of the data point. See companion table for precision-based error bars. The absolute averaged emission indices for the fuel flow repeats during the test are depicted in the four panels; upper left CO in black; upper right HCHO in orange; lower left ethene (C2H4) in magenta; and lower right benzene (C6H6) in violet.

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35 Figure A01-E2c. Emission Index for engine SA002 for Toluene, C2-Benzene, Styrene, and Naphthalene. C2-Benzene refers to the sum of the xylene isomers and ethyl-benzene. The four figures depict the emission indices in grey with the precision-based error bar from the entire CFM56-7B24 dataset. The colored data points are the emission index for the species in question averaged for the nominal engine state during the test of engine index SA002. In many cases the precision based error bar for the emission index is smaller in magnitude than the size of the data point. See companion table for precision-based error bars. The absolute averaged emission indices for the fuel flow repeats during the test are depicted in the four panels; upper left Toluene in red; upper right C2-Benzene in light-blue; lower left Styrene in light green; and lower right naphthalene in the larger grey squares.

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36 Figure A01-E2d. Emission Index for engine SA002 using the continuous FID instrument. The grey data points and error bars are the full FID EI dataset collected during the project, which only includes CFM56-7B24 data at MDW 2009. The larger points, in blue are the results for engine 2. Table A01-E3a. Selected test results for engine SA003 (MDW 2009). Aircraft test conducted from 3/4/09 03:45 to 3/4/09 04:30, ambient temperature 270.81K, relative humidity 53%. Fuel Flow 2 N1 2 CO EI s FID EI 2 kg s-1 kg s-1 % % g kg-1 g kg-1 g kg-1 g kg-1 0.0830 20.70 67.5 1.7 6.7 1.4 0.0895 0.0007 20.30 0.14 72.0 0.9 9.5 1.4 0.0953 0.0006 20.10 70.4 1.2 7.6 1.0 0.1020 25.20 38.2 0.4 3.2 0.2 Engine SA_001 Fuel Flow 2 C2H4 EI 2 HCHO EI 2 Benzene EI 2 kg s-1 kg s-1 g kg-1 g kg-1 g kg-1 g kg-1 g kg-1 g kg-1 0.0830 1.880 0.020 1.74 0.06 0.200 0.014 0.0895 0.0007 2.155 0.046 1.99 0.06 0.240 0.011 0.0953 0.0006 2.147 0.031 1.93 0.05 0.230 0.015 0.1020 0.620 0.010 0.77 0.06 0.090 0.003 Engine SA_001 Fuel Flow 2 Toluene EI 2 C2-Benzene 2 Styrene 2 kg s-1 kg s-1 g kg-1 g kg-1 g kg-1 g kg-1 g kg-1 g kg-1 0.0830 0.123 0.006 0.076 0.006 0.112 0.013 0.0895 0.0007 0.134 0.002 0.094 0.003 0.116 0.006 0.0953 0.0006 0.128 0.005 0.085 0.005 0.120 0.011 0.1020 0.051 0.001 0.039 0.001 0.093 0.003 Table Notes. The 2 value is computed as twice the standard error of the fit emission ratio converted to emission index. When multiple data points have been averaged at the noted fuel flow rate, these errors have been added in quadrature.

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37 Figure A01-E3b. Emission Index for engine SA003 for CO, HCHO, C2H4, and C6H6. The four figures depict the emission indices in grey with the precision-based error bar from the entire CFM56-7B24 dataset. The colored data points are the emission index for the species in question averaged for the nominal engine state during the test of engine index SA003. In many cases the precision based error bar for the emission index is smaller in magnitude than the size of the data point. See companion table for precision-based error bars. The absolute averaged emission indices for the fuel flow repeats during the test are depicted in the four panels; upper left CO in black; upper right HCHO in orange; lower left ethene (C2H4) in magenta; and lower right benzene (C6H6) in violet.

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38 Figure A01-E3c. Emission Index for engine SA003 for Toluene, C2-Benzene, Styrene, and Naphthalene. C2-Benzene refers to the sum of the xylene isomers and ethyl-benzene. The four figures depict the emission indices in grey with the precision-based error bar from the entire CFM56-7B24 dataset. The colored data points are the emission index for the species in question averaged for the nominal engine state during the test of engine index SA003. In many cases the precision based error bar for the emission index is smaller in magnitude than the size of the data point. See companion table for precision-based error bars. The absolute averaged emission indices for the fuel flow repeats during the test are depicted in the four panels; upper left Toluene in red; upper right C2-Benzene in light-blue; lower left Styrene in light green; and lower right naphthalene in the larger grey squares.

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60 Table A01-E13a. Selected test results for engine SA013 (MDW 2010). Aircraft test conducted from 2/16/10 04:30 to 2/16/10 05:15, ambient temperature 269.71K, relative humidity 80%. Fuel Flow 2 N1 2 CO EI 2 -1 -1 -1 kg s kg s % % g kg g kg-1 0.0860 0.0014 20.55 0.42 100.033 3.885 0.0920 0.0000 20.05 0.21 86.645 3.029 0.0973 0.0005 20.20 0.45 78.808 3.093 0.0997 0.0015 25.37 0.45 65.287 3.780 Engine SA_001 Fuel Flow 2 C2H4 EI 2 HCHO EI 2 Benzene EI 2 -1 -1 -1 -1 -1 -1 -1 kg s kg s g kg g kg g kg g kg g kg g kg-1 0.0860 0.0014 3.118 0.150 2.285 0.147 0.323 0.016 0.0920 0 2.450 0.101 1.875 0.111 0.251 0.013 0.0973 0.0005 2.070 0.098 1.580 0.104 0.209 0.012 0.0997 0.0015 1.577 0.149 1.290 0.124 0.165 0.025 Engine SA_001 Fuel Flow 2 Toluene EI 2 C2-Benzene 2 Styrene 2 kg s-1 kg s-1 g kg-1 g kg-1 g kg-1 g kg-1 g kg-1 g kg-1 0.0860 0.0014 0.191 0.012 0.155 0.008 0.138 0.009 0.0920 0.0000 0.144 0.008 0.106 0.006 0.108 0.007 0.0973 0.0005 0.118 0.009 0.083 0.006 0.087 0.007 0.0997 0.0015 0.095 0.019 0.075 0.012 0.076 0.014 Table Notes. The 2 value is computed as twice the standard error of the fit emission ratio converted to emission index. When multiple data points have been averaged at the noted fuel flow rate, these errors have been added in quadrature.

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61 Figure A01-E13b. Emission Index for engine SA013 for CO, HCHO, C2H4, and C6H6. The four figures depict the emission indices in grey with the precision-based error bar from the entire CFM56-7B24 dataset. The colored data points are the emission index for the species in question averaged for the nominal engine state during the test of engine index SA013. In many cases the precision based error bar for the emission index is smaller in magnitude than the size of the data point. See companion table for precision-based error bars. The absolute averaged emission indices for the fuel flow repeats during the test are depicted in the four panels; upper left CO in black; upper right HCHO in orange; lower left ethene (C2H4) in magenta; and lower right benzene (C6H6) in violet.

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62 Figure A01-E13c. Emission Index for engine SA013 for Toluene, C2-Benzene, Styrene, and Naphthalene. C2-Benzene refers to the sum of the xylene isomers and ethyl-benzene. The four figures depict the emission indices in grey with the precision-based error bar from the entire CFM56-7B24 dataset. The colored data points are the emission index for the species in question averaged for the nominal engine state during the test of engine index SA013. In many cases the precision based error bar for the emission index is smaller in magnitude than the size of the data point. See companion table for precision-based error bars. The absolute averaged emission indices for the fuel flow repeats during the test are depicted in the four panels; upper left Toluene in red; upper right C2-Benzene in light-blue; lower left Styrene in light green; and lower right naphthalene in the larger grey squares.

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63 Testing on the V2527-A5 additional study in the future, but the single test described here should not be over-interpreted. At the conclusion of the MDW 2010 testing campaign, The ICAO databank HC EI for the V2527-A5 is 22 times lower the mobile laboratory was driven to Chicago ORD airport in than the HC emission index tabulated for the CFM56-7B24. order to collect abbreviated test data on engine technologies As a result, the limits of detection in the analytical instrumenta- in addition to the CFM56 type engine. One of the two aircraft tion preclude assigning any speciated VOC emissions for this tested in this phase of the project, provided by United Air engine type beyond formaldehyde. Using the tabulated emission Lines, was an A320-232 equipped with the V2527-A5 engine index of 0.105 g HC per kg fuel, and the ratio of HCHO to HC variant. The sampling style employed was identical to that measured in the MDW 2009 tests (0.2 g HCHO per "g" HC), used in the MDW 2009 phase, where the mobile laboratory it suggests the HCHO EI for this engine type at the 7% thrust was maneuvered behind the aircraft. fuel flow rate should be 21 mg HCHO per kg fuel. In the right Figure A01-Va depicts the results of the determination of hand panel of Figure A01-Va, this estimate is quite close to CO and HCHO emission indices as a function of fuel flow what is actually observed at the fuel flow rate of 0.128 kg s-1. noted in the cockpit. All of the data collected in this test, This would suggest that the dependence of HCHO EI on {engine 1, engine 2 and at distances where the sample was ambient temperature is weaker than that observed in the a mixture of both engines} has been plotted together. Where CFM56 engine testing. the digital readout in the cockpit indicated a difference in fuel flow between the two engines and the sampling distance was such that we could not plausibly argue the sample was domi- Testing of the PW4090 nated by one engine or the other, the average has been used Following the testing of the V2527-A5, the United Air Lines in the graphical representation. personnel suggested that a 777-222ER equipped with PW4090 The CO EI tabulated in the ICAO databank has been placed be tested next. The data from this test are tabulated here, on the figure as a black diamond. The dashed line is approxi- however it was unscheduled work and as a result the precise mately 37% greater than the ICAO databank value at a fuel engine settings required to match the ICAO 7% engine condi- flow rate of 0.128 kg/s. This qualitatively agrees with the trend tion were not known during the test. The PW4090 represents observed in the CO EI temperature dependence in other work a much higher thrust engine class then either of the CFM56 (AAFEX) as well as the temperature dependence derived or V2500 engine types and we had to trust the experience of for the near-idle hydrocarbon EI (see main project narrative). the maintenance crew we were working with in order to The simple two point temperature dependence derived from keep a safe condition for the mobile laboratory maneuvering this single engine test indicates the engine is slightly less behind the idling engine. dependent on ambient temperature than the CFM56-7B24 Due to the spontaneous nature of the test, we did not attempt and CFM56-2C1 engine tests. This engine type does warrant to operate the engines independently. The test matrix was Figure A01-Va. Emission Indices for CO and HCHO for the V2527-A5 test. The left hand panel depicts the measured CO EI as a function of engine fuel flow rate. The right hand panel plots the measured HCHO EI (in mg kg21) as a function of fuel flow rate.

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64 Figure A01-Pa. CO Emission Index vs Fuel Flow for PW4090. The Grey squares are the CO emission index plotted vs engine average fuel flow (see text for details). The black diamond is the ICAO reference CO EI at 7% fuel flow rate. simplified to include the conditions described in Appendix B (N1 = 20% relative to N1 = 25%). Additional work will be as ground-idle with zero bleed air demand, ground-idle with needed to extract a quantitative comparison with ICAO for nominal bleed air demand and at N1 = 25%. This last test this engine test. condition was a guess on what N1 setting would correspond An additional evaluation can be performed that com- to 7% thrust for this engine. The Figure A01-Pa depicts the pares the hydrocarbon profile of this "large engine" to the CO emission index vs. the fuel flow rate for the test. Note that it more thoroughly tested CFM56 engines. The HC EI at 7% is clear that the ICAO 7% fuel flow condition was not matched tabulated in ICAO is nearly identical for the PW4090 and in this test. The range of noted N1 rotation speeds for the clus- the CFM56-7B24, indicating that unlike the comparison ter of data measured below 0.24 kg s-1 were all in the range of between the CFM56-7B24 and the V2527-A5, there should 18.9 to 20.0%. The range of noted N1 rotation speeds for the at least be hydrocarbons present of a similar magnitude to three measurements above 0.3 kg s-1 were all 24.1 to 25.6%. verify the hydrocarbon profile for the selected species mea- In this engine test, the effect bleed air demand on fuel flow sured at this test. Figure A01-Pb depicts the correlation of was considerably less than was observed in the CFM56 tests. the emission indices of 1,3-butadiene and formaldehyde for The comparison to the ICAO CO certification value is the PW4090 test. challenged because the fuel flow rate needed to match the 7% The grey dashed line in Figure A01-Pb is a linear least squares thrust condition was apparently not met. If the dashed line fit to the data forced through the origin which suggests the drawn between the cluster of CO points is taken to represent relationship between 1,3-butadiene and formaldehyde is the CO emission index at intermediate fuel flows, then the 1034 mg:g-1. This compares favorably to the current value comparison could be termed "favorable". The very puzzling asserted in the SPECIATE profile (137 mg:g-1). aspect of this comparison, however is the apparent agreement. Additional hydrocarbon ratios tabulated in Table A01-Pc The ambient temperature was 270.3K (RH = 67%) for this test suggest generally good agreement with the SPECIATE profile is sufficiently less than the ICAO reference temperature of for this test (EPA 2008). While the compound ratios for the 288K that the understanding of ambient temperature depen- other VOCs, except for ethene, tend to be lower than that dence developed in this study (based on the CFM56 tests) predicted by SPECIATE, such a good correlation might not suggests the measured CO should have been greater. The have been expected given that SPECIATE is derived from qualitative observation of emission index trend with fuel CFM56 engine (EPA 2008). This singular comparison should flow is matched here though. The emission index for CO not be over interpreted, but it does suggest that VOC emis- (and the hydrocarbons not depicted) is approximately double sion profile is not highly dependent on combustor design.

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65 Figure A01-Pb. 1,3-butadiene EI vs. HCHO EI. The PW4090 test results for the NO-MS measurement of 1,3-butadiene are plotted against the QCL measurement of HCHO. The color scaling indicates the time since the engines were turned on. The ratio between these hydrocarbon species does not depend on the engine warm up. Additional engines needed to be studied to further corroborate which we find that nearly all of the VOC exhaust emissions this finding. components scale in a near-linear relationship with one another under low power conditions. We refer to this obser- vation as near-idle emissions scaling. In this section, we first A02--Additional Findings briefly review the instruments and sampling methods and on the Near-Idle Hydrocarbon then present results that illustrate the near-idle VOC emissions Emission Profile scaling phenomenon. This is followed by a discussion of how Our characterization of VOC emissions from Jet aircraft this relationship can be used to interrogate our analytical engines has spanned a period of 8 years and 12 separate mea- methodology, probe sampling effects, gaps in existing VOC surement opportunities (Herndon et al. 2006, Herndon et al. speciation profile, and the validity of predicting VOC emissions 2009, Knighton et al. 2007, Yelvington et al. 2007) (need to that were not directly measured. include AAFEX NASA reference). During these studies, we Before we present any data, it is important to review have observed a consistent and repeatable phenomenon, in the analytical methods and sampling strategies employed. Sampling strategies differed in how the engine exhaust samples were delivered to the instruments. During MDW Table A01-Pc. PW4090 compound ratios. 2009, a down-wind plume intercept approach was used, which allowed the exhaust to cool and dilute naturally into (g / g formaldehyde) uncertainty SPECIATE ambient air. The concentration of the components within Ethane 1.30 0.04 1.25 the exhaust plume dilutes continuously with down-wind 1,3 butadiene 0.103 0.004 0.137 distance and is modulated further by wind speed and direc- Benzene 0.128 0.006 0.137 tion. The plume intercept method requires that all of the Toluene 0.036 0.006 0.052 instruments operate at 1 Hz. Extraction probes were used C2-benzenes 0.046 0.008 0.050 during DAL 2009 and MDW 2010 to transport the exhaust sample to the instruments. At DAL 2009, three different Naphthalene 0.032 0.002 0.044 extraction probes were used and differed on how and where

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66 Table A02-1. Instrumental methods used for the measurement of the selected VOCs. Compound MDW 2009 DAL 2009 MDW 2010 formaldehyde QCL QCL QCL ethene QCL QCL QCL + + acetaldehyde PNL-H3O MSU-H3O PNL-H3O+ + 1,3-butadiene MSU-NO+ ---- MSU-NO benzene MSU-NO+ MSU-H3O+ MSU-NO+ toluene MSU-NO+ MSU-H3O+ PNL-H3O+ styrene MSU-NO+ MSU-H3O+ PNL-H3O+ + C2-benzenes MSU-NO+ MSU-H3O MSU-NO+ + naphthalene MSU-NO+ MSU-H3O PNL-H3O+ the exhaust was diluted. At MDW 2010 a single extraction the plots, however, is not random. In most cases, the profiles probe was deployed. exhibit a linear ray for each aircraft. It is from this behavior VOC measurements were made using a total of four differ- that the term near-idle VOC scaling concept arose. While it ent instruments, one of which (MSU PTR-MS) was operated in is not clear why near-idle VOC scaling should exist, it does two different chemical reagent ion modes. Formaldehyde and collapse much of the variability observed in the absolute ethene were measured spectroscopically using QCL TILDAS EI measurements. This is important, because it allows us to instruments. The remaining VOCs were measured using a identify which measurements don't follow the trend and then pair of chemical ionization mass spectrometers, except at DAL interrogate those measurements more carefully. 2009 where only one instrument was deployed. Table A02-1 We can now examine the profiles shown in Figure A02-1 lists VOC species measured and identifies which instrument more carefully with the goal of identifying the source or method was used. The compound list in Table A02-1 rep sources that lead to the observed variability. Formaldehyde resents only those compounds that were measured during all and acetaldehyde both show similar behavior except for the of the deployments. The instruments are designated as follows: five formaldehyde data points that lie below the rest of the QCL represents the QCL TILDAS instruments. MSU H3O+ and data. These data were all measured using the gas probe during MSU NO+ refer to the MSU PTR-MS operated in standard DAL 2009. This is not a sampling anomaly as the PTR-MS proton transfer (H3O+) or alternative ion (NO+) mode. The measurement of formaldehyde exhibited an identical result. PNL PTR-MS was only operated in the standard H3O+ mode. It is not immediately obvious why formaldehyde should be lost In cases where the same species was measured by more than or consumed within the gas probe, but it certainly casts some one instrument, only the "best" measurement is reported. At doubt about the use of this type of probe. In fact, it leads MDW 2010 the PNL PTR-MS measurements were chosen one to question if the reason why both formaldehyde and for styrene and naphthalene because of evidence that there acetaldehyde measurements from MDW 2009 lie above those were interferences to NO-MS measurements. For toluene, made using extractive probes isn't the result of a probe effect. the calibration of the NO-MS is less robust and the PTR-MS We also note that there is some curvature in the formaldehyde measurement was considered as the best. and acetaldehyde plots at the highest emissions. This result The near-idle VOC scaling phenomenon is illustrated seems to suggest that the fuel continues to decompose to in Figure A02-1, where we have taken the EI data for each ethene but that combustion begins to diminish under these of the VOC species and plotted it versus the corresponding conditions. ethene measurement. The plot colors identify the different Inspection of the other profiles shows that there is measurements, MDW 2009 (red), DAL 2009 (green) and MDW inherently more variability in the hydrocarbon emissions, 2010 (blue), while the different aircraft tested are identified in part due to their lower concentrations (molar basis). by a different marker style. Overall, there is also a strong It is logical to question whether this variability originates suggestion that all of the measurements are correlated in a from the measurements or reflects differences in the engine near-linear fashion even though these profiles show varying exhaust emissions. In cases where the results show obvious degrees of scatter. Closer inspection reveals that the scatter in differences between the test periods (i.e., 1,3-butadiene),

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67 Figure A02-1. Near-idle VOC emissions scaling profiles. Marker color indicates the measurement date and location. Marker styles identify the different aircraft.

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68 it seems logical to question if the variability isn't the result scaling be applied? To address this question we need to exam- of the analytical measurement. An incorrect instrument ine how our speciated VOC emissions vary with CO and UHC calibration factor could lead to such a result, even though (unburned hydrocarbons). every effort was made to check the calibrations before, during Figures A02-2 and A02-3 examine the relationship between and after the studies. When differences are observed within the emission of ethene with those of CO and UHC as measured the aircraft studied at a given test, it would appear that the with an FID. Two very different behaviors emerge. When the variability is related either to the fuel, the engine or some ethene EI is less than 2g/kg the ethene emissions appear to other unknown external influence. scale in a near-linear fashion with both CO and UHC. As the We can now examine the results of this study to that reported ethene EIs increase above 2g/kg nonlinearities appear. The elsewhere, such as SPECIATE or our previous AAFEX results CO emissions stop increasing at the same rate and the UHC (Anderson et al. 2010, EPA 2008). To make this comparison emissions start increasing more rapidly with respect to we have normalized our data to that of ethene and fit the fre- ethene. This result suggests that the engine reaches a condition quency distribution to a Gaussian. The centroid of the Gaussian where it is no longer burning most of the fuel. If one views distribution is taken as the best value with the width represent- combustion as a simple two step process, where the fuel pyro- ing the uncertainty. For 1,3-butadiene the average and standard lyzes decomposes into smaller molecules (ethene) followed deviation are reported, because the frequency distribution is by combustion (oxidation), then it follows that ethene pro- bimodal. These results are summarized in Table A02-2 along duction would continue longer than the combustion process. with those reported in SPECIATE (EPA 2008) and from Likewise, the ethene production will diminish relative to the AAFEX for JP-8 (Anderson et al. 2010). The ACRP data agree UHC at the point where unburned fuel actually escapes within the uncertainty limits with the other measurements from the combustor. While this argument explains the except for acetaldehyde, which is approximately 30% high. relationship between ethene and UHC, why don't the VOCs Near-idle VOC emissions scaling allows us to decouple in Table 2 (i.e., the aromatics) exhibit more non-linearity at changes in the VOC composition of the exhaust from the the higher EIs? variability in the absolute VOC EIs exerted by engine power Some of the species in Table A02-2 are only combus - and ambient temperature. The near-linear relationships tion products and are not present in the liquid fuel. Others, observed in Figure A02-1 and the overall agreement between such as the aromatics, are both combustion products and the ethene normalized EIs found here with that reported components of the liquid fuel. It is beyond the scope of elsewhere, strongly suggests that the VOC composition is this report to do a detailed examination of how the VOC relatively insensitive to engine condition or fuel composition, emissions vary with fuel composition, but the observation at least over the limited range of engines studied and fuel of the near-idle VOC emission scaling exhibited by the compositions. The relative consistency of the VOC exhaust aromatics infers that, under the conditions studied, their composition allows one to then project the emissions of presence in the exhaust is dominated by combustion and chemical species not directly measured by scaling the emis- not the escape of unburned fuel into the exhaust. In con- sions to that of ethene. The obvious question arises. Over trast the FID is most sensitive to the presence of large what range of conditions can the near-idle VOC emission hydrocarbons, such as the long chained alkanes that make Table A02-2. Comparison of compound EIs normalized to ethene. Species Speciate AAFEX ACRP EIx/EIethane EIx/EIethene EIx/EIethene formaldehyde 0.80 0.75 0.79 (0.12) acetaldehyde 0.28 0.27 0.35 (0.04) 1,3-butadiene 0.11 ---- 0.10 (0.03) Benzene 0.11 0.12 0.10 (0.04) Toluene 0.042 0.057 0.056 (0.007) Styrene 0.020 0.026 0.043 (0.016) a C2-benzenes 0.040 (0.053) 0.047 (0.026) Naphthalene 0.035 0.028 0.028(0.015) (a) The PTR-MS determination reports the sum of the C2-benzenes + benzaldehyde. The data entry here has been adjusted to correct for the benzaldehyde contribution assuming that 43% of the response is from benzaldehyde.

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69 Figure A02-2. Correlation scatter plot of ethene EI versus unburned hydrocarbon UHC EI. up a large fraction of the liquid fuel. The bias in the UHC Scaling emissions from either CO or UHC measurements towards the presence of unburned fuel is further exacer using databases such as SPECIATE (EPA 2008) need to recog- bated by the fact that FID detector response is diminished nize the limits where these relationships become non-linear. to carbons that are bonded to an oxygen. The FID is essen- Anecdotally, it appears that there is little error introduced tially blind to the presence of formaldehyde, which rep- under moderate to warm ambient temperatures. A linear resents approximately 12% of the organic carbon in the scaling to CO or UHC is not appropriate at low ambient exhaust. temperatures. Figure A02-3. Correlation scatter plot of ethene EI versus CO EI.

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70 Near-idle VOC emissions scaling can be a valuable tool for Herndon, S.C., T. Rogers, E.J. Dunlea, R.C. Miake-Lye, and B. Knighton. projecting jet engine exhaust emissions, providing it is properly 2006. Hydrocarbon emissions from in-use commercial aircraft during airport operations. Environmental Science and Technology. applied. Its validity, however, is only as good as the knowl- 40 (14): 44064413. edge of VOC speciation profile. Databases such as SPECIATE Herndon, S.C., E.C. Wood, M.J. Northway, R.C. Miake-Lye, (EPA 2008) contain extensive listing, but are still not com- L. Thornhill, A. Beyersdorf, B.E. Anderson, R. Dowlin, W. Dodds, prehensive and only identify 70% of the VOC mass emissions. and W.B. Knighton. 2009. Aircraft Hydrocarbon Emissions at The bulk of the missing mass is most likely in the higher Oakland International Airport, Environ Sci. Technol. 43. 17301736. Herndon, S.C., et al. 2004. NO and NO2 Emissions Ratios Measured molecular hydrocarbons, which are difficult to conclusively from in use Commercial Aircraft during Taxi and Take-Off. Environ. identify by GC/MS because of their similar mass spectral Sci. Technol. 38: 60786084. fragmentation patterns. There is also evidence from studies Knighton, W.B., T. Rogers, C.C. Wey, B.E. Anderson, S.C. Herndon, conducted elsewhere (Anderson et al. 2010, Timko et al. 2011) P.E. Yelvington, and R.C. Miake-Lye. 2007. Quantification of using a GC/PTR-MS that indicates the presence of unsaturated Aircraft engine Hydrocarbon Emissions Using Proton Transfer Reaction Mass Spectrometry. Journal of Propulsion and Power 23 aldehydes, corresponding to C4H6O and C5H8O that are not (5): 949958. included in SPECIATE (EPA 2008). These species are more Timko, M.T., S. Herndon, E. de la Rosa Blanco, E. Wood, Z. Yu, likely to be on the HAPs list and thus represent species of R.C. Miake-Lye, W.B. Knighton, L. Shafer, M. DeWitt, and concern. E. Corporan. 2011. Combustion Products of Petroleum Jet Fuel, a Fischer Tropsch Synthetic Fuel, and a Biomass Fatty Acid Methyl Ester Fuel for a Gas Turbine Engine. Combust. Sci. Technol. References Cited in Appendix A in press. Yelvington, P.E., S.C. Herndon, J.C. Wormhoudt, J.T. Jayne, R.C. Anderson, B.E., et al. 2010. Alternative Aviation Fuel Experiment Miake-Lye, W.B. Knighton, and C.C. Wey. 2007. Chemical Specia- (AAFEX) Rep. tion of Hydrocarbon Emissions from a Commercial Aircraft Engine. EPA. 2008. SPECIATE, edited. US EPA. Journal of Propulsion and Power. 23: 912918.