A Source Dilution Sampling System for Characterization of Engine Emissions under Transient or Steady-State Operation

Abstract

With increasingly stringent regulations being placed upon engine emissions, an in-depth understanding of engine exhaust composition will be necessary to assess environmental and health impacts and to develop better methods of reducing emission levels. Source sampling systems have commonly utilized partial sampling techniques, which may introduce the potential for particle loss, and steady-state operation, which is incapable of imitating transient engine conditions. In order to simulate atmospheric dilution and aging conditions, maintain proportional sampling throughout temperature excursions during transient operation, and minimize particle loss, while representatively taking multiple samples from the exhaust flow, a full-partial-full source dilution sampling system was developed. The system consists of a critical flow venturi-constant volume system for primary dilution, a thermophoresis-resistant secondary micro-diluter, a residence time chamber, isokinetic sampling probes, multiple sampling trains, and control systems. Further, the system was designed to prevent particle loss and secondary reactions by reducing wall effects, implementing inert materials, optimizing smooth flow transition, and minimizing electrostatic forces. An examination of the system was conducted by performing a tracer study and by determining the variations in flow rates, gaseous concentrations, and PM mass measurements. Further, a statistical analysis was performed to study the capability and performance of the sampling system. The results suggest that the system was capable of collecting similar samples among the sampling trains and displaying sufficient agreement with a certification system. Therefore, the source dilution sampling system developed in this study is suitable for collecting representative samples from an exhaust flow under transient or steady-state conditions.

Investigation of black and brown carbon multiple‐wavelength‐dependent light absorption from biomass and fossil fuel combustion source emissions

“…Numerous other source testing investigations have employed similar techniques to collect fresh emissions, so each sample configuration will only be briefly discussed. Diesel samples were collected from a constant volume sampler (CVS) emission tunnel (Cummins Emission Solutions, Stoughton, WI) in which a subsample stream of primary diluted exhaust was introduced to a residence time chamber and completely mixed with filtered and dried secondary dilution air [ Liu et al ., ; Robinson et al ., ]. The secondary diluted sample was passed through a Dekati thermodenuder (TD, Dekati, Kangasala, Finland) at one of two temperature set points, 30°C as the nondenuded conditions and 300°C as a denuded condition.…”

Comparison of Strategies for the Measurement of Mass Emissions from Diesel Engines Emitting Ultra-Low Levels of Particulate Matter

“…Samples for both the ultra-low emissions gravimetric method and chemical reconstruction method were collected using a source dilution sampling system consisting of a primary dilution tunnel, a secondary-micro diluter, a residence time chamber (RTC), and multiple sampling trains (Liu et al 2008b). The exhaust gas from the engine was piped into a critical flow venturi-constant volume system (CFV-CVS) tunnel where it was mixed with pre-, activated carbon-, and HEPA-filtered air at a rate of 1.298 m 3 /s.…”

“…Other studies have also shown that implementation of aftertreatment systems, such as DPFs, alters emissions compositions (Lev-on et al 2002;Liu et al 2008a). In comparison to the high-PM emissions of older engines, the ultra-low PM emissions of modern engines have been shown to exhibit a less stable composition (Birch and Cary 1996;Kleeman et al 2000;Liu et al 2008b). The solid fraction of PM in ultra-low emissions is largely filtered by the DPF, leaving an increased organic fraction and yielding a relative enrichment in semi-volatile organic matter.…”

Emission factors of domestic coal-burning braziers

“…Before conducting test experiments, the sampling dilution system components were disassembled, cleaned, air dried, assembled, and 'tested for leaks to prevent contamination from the surrounding air' 37 to avoid contamination of the emissions with organic and metal compounds from previous burn sequences. High power compressed air and water were used to remove large particles from the sampling channels.…”