Performance Evaluation of Particle Sampling Probes for Emission Measurements of Aircraft Jet Engines

AbstractConsiderable attention has been recently received on the impact of aircraft-produced aerosols upon the globalclimate. Sampling particles directly from jet engines has been performed by different research groups in USand Europe. However, a large variation has been observed among published data on the conversionefficiency and emission indexes of jet engines. The variation results surely from the differences in testengine types, engine operation conditions, and environmental conditions. The other factor that could resultin the observed variation is the performance of sampling probes used. Unfortunately, it is often neglected inthe jet engine community. Particle losses during the sampling, transport and dilution processes are often notdiscussed/considered in literatures. To address this issue, we evaluated the performance of one samplingprobe by challenging it with monodisperse particles. A significant performance difference was observed onthe sampling probe evaluated under different temperature conditions. Thermophoretic effect, non-isokineticsampling and turbulence loss contribute to the loss of particles in sampling probes. The results of this studyshow that particle loss can be dramatic if the sampling probe is not well designed. Further, the result allowsones to recover the actual size distributions emitted from jet engines.IntroductionIt is known that atmospheric aerosols play a key role in the Earth's radiation balance, and thereby stronglyinfluence the global climate. Due to the heavy air travel nowadays, aircraft engines directly emit a greatamount of both soot and sulfuric acid particles to the upper troposphere and lower stratosphere. Theseparticles may have negative impact on climate through the processes of inducing the formation of new iceclouds (contrails), modifying physical properties of existing cirrus clouds, and providing additional surfacearea for heterogeneous chemical reactions such as ozone destruction.In order to address this issue, researches have been performed to evaluate the emission of jet engines whenaircrafts are either on ground or in air. To be able to understand the detail particle formation processes,sampling particles from jet engine exhaust or in the near field has been performed by NASA Subsonic aircraftContrail and Cloud Effect Special Study (SUCCESS) and SULFUR series experiments by German agency,Deutsche Forschungsanstalt fur Luft- and Raumfahut (DLR). For the sulfate particle measurement, the valuesof _, the conversion efficiency of fuel sulfate to sulfate in the forms of SO3 and H2504, by SUCCESS showedthat _ does not have a strong dependence with the fuel sulfur content (FSC) (1-3). In contrast, studies of DLRshowed a decrease in _ with an increase of FSC (4-5). These variations may result from the differences inengine types, engine operation conditions, environmental conditions, and sampling/measuring methods (6). However, a significant difference is found by the comparison of non-volatile particle emission indices (EIs), theamount of pollutant generated per kilogram of fuel burned, measured in NASA B757 exhaust plumes (1, 2)NASA/CR--2001-211201 1