SAE International, based in Warrendale, Pennsylvania, has published a new recommended practice for assessing the amount of nonvolatile particulate matter (nvPM) that exits aircraft engine exhaust nozzles. ARP6481: Procedure for the Calculation of Non-Volatile Particulate Matter Sampling and Measurement System Losses and System Loss Correction Factors recommends calculation methods, uncertainties, and limitations of the system loss correction factors and supplies a Microsoft Excel® software tool.
Aerospace – like any other modern industry – is shifting toward more ecologically responsible operations. For instance, aircraft engine designers are constantly developing powerplants that can deliver more power and range with less fuel. Another major consideration for engine design engineers is the amount of nvPM, or “aerosol,” emissions that are produced during engine operation.
However, aerosol sampling has an inherent problem of sampling system losses. This has been known since the beginning of the 1900s. When sampling aerosol emissions, the measurement instruments are often found at the end of long sampling systems – sometimes as long as 35 meters. This distance results in a considerable amount of aerosol being attached to the walls of the sample line and other system components.
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The new method published by SAE is used to measures size dependent particle losses in a sampling and measurement system utilizing the aerosol mass and number concentrations measured at the end of an emissions sampling system. Loss mechanisms including thermophoretic – which has a very weak size dependence – and size dependent losses are considered in this method along with the uncertainties due to both measurement error and the assumptions of the method. The results of this system loss assessment allow development of estimated correction factors for aerosol mass and number concentrations to account for the system losses facilitating estimation of the aerosol mass and number at the engine exhaust nozzle exit plane.
Ideally, design engineers who work to improve combustion technology and reduce engine emissions will implement this corrective function and use aerosol concentrations at the engine exit plane rather than the concentrations measured at the instruments.
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Furthermore, aerosol sampling system losses are an issue in any industry that is concerned about understanding aerosols in their processes, such as industries which effect air quality and need to monitor aerosol emissions, such as automotive, marine, semiconductor, chemical manufacturing, pharmaceuticals, and power plant industries.
ARP6481 was developed by the SAE E-31 Aircraft Engine Gas and Particulate Emissions Measurement Committee. The E-31 committee addresses all facets of aircraft exhaust emissions measurement, including tools, methods, processes, and equipment. It is responsible for standardizing measurement methods of emissions from aircraft, including isolated combustor systems. The group is comprised of four subcommittees dedicated to creating, preparing, and maintaining all relevant specifications, standards, and requirements for aircraft exhaust emissions measurement.
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William Kucinski is content editor at SAE International, Aerospace Products Group in Warrendale, Pa. Previously, he worked as a writer at the NASA Safety Center in Cleveland, Ohio and was responsible for writing the agency’s System Failure Case Studies. His interests include literally anything that has to do with space, past and present military aircraft, and propulsion technology.
Contact him regarding any article or collaboration ideas by e-mail at email@example.com.