| Summary: | The aerosol diluter characteristics of three different systems, the single-stage and the two-stage TSI 379020A rotary disk thermodiluters and Dekati FPS-4000 ejector diluter, were tested using gases and particles over a range of dilution ratios. The upstream and downstream gas and particle concentrations of the diluters were measured in real-time to compute the actual dilution ratio achieved by the three systems. Dilution ratios from approximately 15 to 100 were found to fall within the expected operating error margin of ± 10% for CO2 and CH4. Dilution ratios covering a similar range were also achieved to within ± 10% for particles with diameters from 9.3 to 200 nm. However, when engine exhaust was sampled, significant loss of particles smaller than 29.4 nm occurred during the dilution process. As the dilution ratio increased, the deviation from the expected value increased due to an increase in measurement uncertainty.
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