Simulation of Low Level Vehicle Exhaust Emissions for Evaluation of Sampling and Analytical Systems 2001-01-0211

The Vehicle Exhaust Simulator is a tool developed to evaluate the performance of vehicle emissions sampling and analytical systems. Simulating a vehicle's emissions with accurate and repeatable equipment, rather than using a vehicle to produce emissions, eliminates several sources of variability (e.g. driver, dynamometer, vehicle) and isolates the performance of the sampling and analytical systems. Use of the Vehicle Exhaust Simulator includes: diagnosing test site problems, tracking performance over time, establishing correlation between emissions sites, and acceptance testing of new emissions sampling and analytical equipment.

The Vehicle Exhaust Simulator was developed to emulate emissions from low-emitting gasoline vehicles. Federal Test Procedure (FTP) 3-phase bag values (THC, CO, CO₂, and NO_x) from an Ultra Low Emissions Vehicle (ULEV) have been used for most of the testing. The Simulator consists of five Mass Flow Controllers (MFCs), a ±15 volt power supply, a mixing chamber, stainless steel plumbing, a 2.83 m³/min centrifugal blower, and a laptop computer with LabVIEW™ software and analog input/output capability. A custom LabVIEW™ program sends independent 0-5 volt signals to each MFC to control the amount of each emissions constituent (bottled gases) to be injected. The software also records 0-5 volt output signals from each MFC proportional to the MFC's metered flow. The emissions targets and known bottled gas concentrations (1% NIST traceable) are used to accurately simulate the exhaust of the vehicle with high repeatability. The gases are combined in a mixing tube, which closely resembles a vehicle tailpipe with a marmon flange. A moveable cart houses the equipment and is used on the emissions test site in place of a vehicle.

The investigations discussed in this paper were designed to (1) quantify the repeatability and accuracy of the vehicle exhaust simulator “constant mass” injection mode, and (2) determine the feasibility of using the Vehicle Exhaust Simulator as a means for aldehyde/keytone sampling system prove out. This paper will also discuss MFC flow calibration standards, and recommended simulator enhancements and future investigations.