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8 Exhaust Emissions from In-Use General Aviation Aircraft standard times-in-mode are as defined by the ICAO for commercial airports; however, these times may not always be appropriate for typical operations at many GA airports. The develop- ment of GA-specific times in mode was beyond the scope of this research. With the defined power states and known times in mode, it is possible to construct a landing take-off cycle (LTO) for an airplane; for example: idle, taxi, take-off, climb-out, approach, final approach, taxi, and idle. The cruise state is not included in the LTO frameworkâcruise emissions, while important for national inventories, are not relevant when considering emissions at the airport. For a given aircraft, the emission indices can be multiplied by fuel flow and the times in mode to yield an emission burden. The burden represents the amount of pollutant emitted by a given engine over the course of the LTO and will be expressed in units of grams of pollutant per engine (g/engine). Any given airport will have a certain number of operations per unit time. An operation in this sense refers to the number of LTO cycles that occur at the airport. The airport will also have a char- acteristic fleet, where the number and type of aircraft are known. Each aircraft will have a known airframe type (e.g., Cessna 172), engine model type (e.g., Lycoming O-320-E2G), and number of engines per aircraft (1 or 2). With this known information about the airport fleet, a burden for each aircraft can be calculated and summed to produce the final emission estimate for the whole airport. This type of estimate is often done before (a âbaseline scenarioâ) and after (âupdated scenarioâ) some proposed change. The FAA-mandated tool used to perform these calculations is the AEDT. Prior to 2016, the Emission and Dispersion Modeling System (EDMS) was the mandated software. Both pieces of software have the same small set of built-in emission indices, which for piston engines amounts to eight different types of piston engines (see Appendix P). This limited data can now be supple- mented by the new EIs measured over the course of this project. Test Procedures To measure a large number of different engines, engine tests were performed on the ground with real in-use aircraft. The measurement equipment sampled from a probe placed behind the aircraft (no contact). The pilot was instructed to operate the aircraft at different simulated power states (e.g., idle, take-off, and so forth) and an observer in the passenger seat noted relevant cockpit parameters. A primary goal of ACRP Project 02-54 was to supplement the available data on GA engine emissions. To maximize the number of engines measured, measurement equipment was brought to GA airports and ground testing of the local aircraft fleet was done. Flight instructors or owner- pilots operated the aircraft in exchange for hourly fees and/or fuel vouchers. All measurements were performed using a no-contact probe set up 1 to 10 meters behind the tail of the aircraft. Figure 2-2 shows a typical sampling setup for a propeller plane. An alternative type of engine testing involves laboratory measurements of an engine in a dyna- mometer setup (i.e., no aircraft, highly controlled input parameters like fuel flow and torque). While providing detailed information on engine operation, this type of test cannot compete with the low relative cost per engine sampled of real in-use testing. Furthermore, testing the engine in the airframe is more representative of true conditions at a GA airport where many different engine/airframe combinations are operated by many different pilots in different ways. Measurement campaigns were conducted in the spring and fall to avoid large extremes in temperature. Test airports were also at similar altitudes to avoid large differences in ambient pressure. Ambient temperature and pressure are reported for each measured emission index, but no further correction has been made.
Research Approach 9 Two measurement platforms were used: the Aerodyne Mobile Lab (AML) supported instru- mentation for gas-phase measurements; the Aerodyne trailer, towed by a pickup truck, supported instrumentation for all particulate phase measurements. A third vehicle towed a generator for power while stationary. These three vehicles are shown in Figure 2-3 (see also Figure 2-4). The suite of instrumentation is described in more detail in Appendixes G and H. A welded steel tripod with narrow cross-section was used to support sampling lines for gas and particle-phase measurements. The measurement tripod is visible in the center of the frame of Figure 2-3, with Figure 2-2. Preparing for a test of a Lycoming O-320 engine. The tripod to the right of the image supports two sampling lines for gas-phase and particle-phase measurements, respectively. Figure 2-3. Measurement setup. The tow-behind trailer to the left houses the particulate matter instrument suite. The white truck in the middle is the Aerodyne Mobile Laboratory, housing the gas-phase instrumentation and data acquisition computers. The red truck to the right is towing a construction generator that powers all the instrumentation.
