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66 Exhaust Emissions from In-Use General Aviation Aircraft by the pilot (as discussed in the section âPilot Mindset on Fuel Mixtureâ). To collect data on real-world engine states, pilots were encouraged to run the engine they way they would typically operate. For engine states that would be characterized as lean and/or higher combustion temperature, the emission index of CO decreases while the NOx emission index increases. In general, this relationship is found in the NOx emission index (see the region of the upper panel where EI CO is less than ~ 400 g/kg), but this is not as strong as the relationship between the emission indices observed in the turbofan combustor. In the case of the piston engine, each cylinder represents Figure F-2. Time Series and Emission Ratio N9184Y, Lycoming O-320-D3G, Engine RPM 5 850. The data is colored the same as the previous figure but is for a different engine state. Figure F-1. Time Series and Emission Ratio N9184Y, Lycoming O-320-D3G, Engine RPM 5 2300. The left hand panel is a time series of HC, CO and CO2. The time series data is stacked to indicate the relative contribution to the total carbon signal. The right hand panel is a correlation plot of the specific carbon monoxide (CO) data with total carbon. Correlations are taken with and without inclusion of background data (BG) as described in Appendix D with the calculated slope (m) and coefficient of correlation (R2) reported. See text for additional discussion.
Variability in Emissions Results from Variability in the Engine 67 Figure F-3. EI NOx and EI HC vs EI CO. All test data are depicted for all engine states. In the upper panel, the NOx emission index is plotted vs the CO emission index. In the lower panel the specific methane emission index emission index is plotted vs EI CO. The marker style is the motor and the coloring is a qualitative estimate of how fuel-rich the motor was being operated. The data points called out as 2300 and 850 are the two engine states depicted in Figures F-1 and F-2 respectively. a discrete combustor with potentially different temperatures that are mixed into the exhaust manifold. The two example test conditions, shown in Figures F-1 and F-2, have emissions of CO, NOx, and CH4 that are chemically consistent with what is known about thermal NOx (DuBois and Paynter 2006, Kerrebrock 1992) and the production of methane during low-temperature combus- tion (Santoni et al. 2011). Taken together, these demonstrate that the EI quantification methods used in this work are diagnostic of the engine combustion characteristics.
68 The gas-phase instruments used during the ACRP Project 02-54 research are listed in Table G-1. This instrument manifest includes a carbon dioxide (CO2) analyzer (LI-COR), two NOx moni- tors (NOx Box, Thermo Scientific) for the separate detection of nitric oxide (NO) and nitrogen oxides (NO + NO2), a cavity-attenuated phase shift spectrometer for nitrogen dioxide detection (CAPS-NO2, Aerodyne Research, Inc.), and a heated flame ionization detector for hydrocarbon detection (HFID, California Analytical Instruments). A tunable infrared laser direct absorption spectrometer measured carbon monoxide, nitrous oxide, and water vapor (TILDAS N2O-mini, Aerodyne Research, Inc.). These instruments are sufficient to measure the three main gas-phase emission indices: carbon monoxide, NOx, and hydrocarbons. To better characterize and understand the aircraft exhaust, additional gas-phase measure- ments were performed. Most of these were focused on characterizing the mix of hydrocarbons emitted. Three additional TILDAS instruments were included to measure additional trace gases, the carbon-containing species methane (CH4), ethane (C2H6), formaldehyde (HCHO), acetylene (C2H2), and ethene (C2H4). A proton-transfer-reaction mass spectrometer (PTR-MS) measured acetaldehyde, acetone, benzene, toluene, sum of xylenes and ethylbenzene, and naphthalene. Routine zeroing of instruments was performed by overblowing the gas-phase inlet with a cylinder of ultra-zero-air before, during, and after each engine test. Routine calibrations were also performed with a set of calibration tanks to assess instrument performance. Zeroed and calibrated data was used to compute all emission ratios. Gas-Phase Measurement Instruments A P P E N D I X G
