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Development of an EPA Interim Particulate Matter Test Method
Robert Howard | Arnold Engineering Development Center (AEDC)
Standards enacted under the United States Clean Air Act (CAA) require accurate estimates of particulate matter (PM) less than 2.5 micrometers in diameter (PM 2.5) emitted from military aircraft. The US Department of Defense (DoD) needs accurate PM 2.5 data to demonstrate conformity in any National Ambient Air Quality Standards (NAAQS) Non-Attainment area where military aircraft will be based. The Joint Strike Fighter (JSF) will replace a wide range of aging military aircraft currently flying in the U.S. and numerous countries. Characterization of the JSF PM emissions is necessary for JSF aircraft basing decisions. The Environmental Protection Agency (EPA) Method 5 formerly used for PM measurements of test facility and turbine engine PM emissions is cumbersome, costly and offers limited PM characterization data. The primary objective of this study was development of an EPA approved PM test method for non-volatile PM that can be applied at the engine exit plane in a manner similar to regulatory measurements of gas species on commercial engines specified by the International Civil Aviation Organization ANNEX16.
The exhaust exiting the engine contains non-volatile PM and volatile gas constituents (precursors) that have a propensity, as the gas cools, to nucleate and form volatile particles (new particle formation) and/or condense and coat non-volatile particles (condensation). There are no volatile particles in the exhaust at the engine exit plane, only their gas phase precursors. New particle formation and condensation occur naturally in the downstream exhaust plume as the exhaust gas mixes (and cools) with the engine bypass and ambient air. New particle formation and condensation can also occur in the sampling line as the sample gas temperature is lowered through interaction with the cooler sample line walls. The objective was to define a sampling process by which non-volatile PM can be measured accurately by eliminating or accounting for the interference of new particle formation and condensation. The approach pursued in this study adds dilution gas to the exhaust sample as it enters the sampling probe (probe-tip dilution) to eliminate, or mitigate, new particle formation and condensation in the sampling line over all engine power level conditions. A ground-level engine test campaign, called the Methodology Development Test, was conducted on an F100-220 military gas turbine engine in 2007 to experimentally investigate issues with sampling, instrument comparisons, instrument calibrations, sample line penetration and engine data representativeness.
The test data provided assessment of a minimally acceptable sample dilution for diluting at the probe tip, the effects of probe-tip versus downstream sample dilution, sample line velocity, and the impact of engine power level on PM sampling parameters. Also, there was significant progress on development of a field method for sample line penetration, PM instrument calibration issues, and defining system performance checks. The test measurement protocol, referred to as the Interim PM Test Method, was successfully demonstrated during the Validation Test in late 2009, again using an F100-220 engine and the diagnostics, probe-rake system, and sampling system developed for JSF applications. This study has successfully developed and demonstrated a PM test methodology for accurate non-volatile PM emissions characterization measurements that can be applied at the exit plane of non-afterburning military engines. The hardware was developed and validated on an F100-220 engine for future application to the JSF F135 engine and will be available for other military engines as required.
This research has been shared with the Society of Automotive Engineers (SAE) E-31 Aircraft Exhaust Emissions Measurement Committee to aid in the development of an International PM measurement procedure for certification of commercial engines. Further research is needed to simplify the extractive sampling methodology and possible development of non-intrusive diagnostics for quantitative measurements of PM mass and number in turbine engine exhaust.