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15 CHAPTER 5 Composition and Physical Properties of Particulate Matter From Aircraft Engines--Knowledge and Gaps Soot (Nonvolatile PM)-- Armed with these new methods for fundamental parame- Knowledge terization, research programs have been funded to charac- terize the PM emissions with respect to size, number, mass, Historically, soot from aircraft engines has been monitored and composition as a function of engine operating condition indirectly through measurement of smoke number. Smoke for a significant subset of engines currently in service in the numbers are a required measurement during engine certifica- commercial fleet. These engines include CFM56-2C1, JT8D- tion testing and have been recorded in the ICAO database since 219, CF6-80A2, CF6-80C2B8F, PW 2037, CFM56-3B1, the mid 1970s. Smoke numbers, required to be reported only CFM56-7B22, AE3007A, PW 4158, RB211-535E-4B, and at the engine power for which it is maximum, are available for CJ610. The engine class most extensively studied is the all large turbine engines currently employed in the commercial CFM56 with a total of 11 engines being examined. For fleet. A smoke number measurement involves drawing a the CFM56 class, measurements have been made at or close known volume of engine exhaust through a filter. Post expo- to the exhaust nozzle (within 2m), in the near-field plume sure, the filter is examined optically and its reflectance relative (~ 10 m, 30 m, and 50 m) and in advected plumes (100 m to a calibrated light source is used to calculate a "smoke num- to 300 m downwind). Smaller datasets exist for the other ber." Clearly a smoke number provides a relative measure of engines studied to date. the sootiness of a particular engine as a function of its opera- Assessment of the results of these studies leads to the tion but it imparts no information on the physical and chemi- following conclusions on PM characteristics and measure- cal properties of the PM such as size, number, shape, mass, ment methods. composition, and reactivity. The inadequacy of smoke number and the need for detailed aircraft engine particulate matter (PM) characteriza- PM Characteristics tion became apparent in the early 1990s as the atmospheric · At the exit plane the exhaust contains nonvolatile or refrac- and environmental scientific communities started to assess tory PM, combustion gases, and the precursors for volatile the impact of aviation emissions on the atmosphere at cruise PM evolution (i.e., sulfate and organics). As the plume altitudes (e.g., NASA's Atmospheric Effect of Aircraft evolves new particles form through nucleation of volatile Program (AEAP)). Since that time groups in the United organics and sulfates and some of the nucleated particles States and Europe have developed and continue to develop agglomerate on the nonvolatile PM surfaces. methods for detailed aircraft engine PM characterization · With respect to the nonvolatile PM from aircraft engines using fundamental physical and chemical parameters. the following characteristics have been established: Around 2000, in response to a request for information from ­ Number-based emission index (EIn) falls in the range of ICAO, the SAE E31 committee established a special PM sub- 1014­1016 particles/kg fuel burned. committee charged with developing a recommended practice ­ Mass-based emission indices (EIm) fall in the range of for aircraft engine PM characterization based on fundamen- 0.01­0.5 g/kg fuel burned. tal physical and chemical parameters.20 ­ Particles tend to have approximately spherical geometry and are made up of aggregates of smaller spherical parti- 20 Society of Automotive Engineers Aerospace Information Report 5892 copy- cles, which tend to be smaller and less highly coagulated right © 2007 SAE. than the chain aggregates typical of diesel PM.