Using a Vehicle Exhaust Emission Simulator (VEES) as a Cross Check Tool for Emission Test Cell Correlation

It is becoming increasingly difficult to obtain good repeatability from running lab vehicle correlation testing, since vehicle variability is so significant at the Low ULEV and SULEV emissions levels. These new emission standards are becoming so stringent that it makes it very difficult to distinguish whether a problem is a result of vehicle variability, test cell sampling or the analytical system. A vehicle exhaust emission simulator (VEES) developed by Horiba, can simulate emissions from low emitting gasoline vehicles by producing tailpipe flow rates containing emissions constituents ( HC, CH₄, CO, NO_x, CO₂ ) injected at the tailpipe flow stream via mass flow controllers. This equipment has replaced one of the internal lab correlation vehicle at the DaimlerChrysler Emission and Fuel Economy Certification Department in Auburn Hills, Michigan and is currently being utilized to check the integrity of the sampling systems in the test cell and to verify correlation from one sampling system to another and from cell to cell. The variability from a typical ULEV vehicle in comparison to the VEES is discussed and analyzed. Bag to modal correlation is also discussed and analyzed. Other scenarios were examined where problems with the sampling and the analytical systems have occurred and the VEES was able to rapidly detect these problems, facilitating effective corrective actions.