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

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.