Measurement of In-Use, On-Board Emissions from Heavy-Duty Diesel Vehicles:Mobile Emissions Measurement System

Emissions tests for heavy-duty diesel-fueled vehicles are normally performed using an engine dynamometer or a chassis dynamometer. Both of these methods generally entail the use of laboratory-grade emissions measurement instrumentation, a CVS system, an environment control system, a dynamometer, and associated data acquisition and control systems. The results obtained from such tests provide a means by which engines may be compared to the emissions standards, but may not be truly indicative of an engine's in-vehicle performance while operating on the road. An alternative to such a testing methodology would be to actively record the emissions from a vehicle while it was operating on-road. A considerable amount of discussion has been focused on the development of on-road emissions measurement systems (OREMS) that would provide for such in-use emissions data collection. Discussed herein is a review of research related to previous in-field and on-board emissions measurement systems, as well as an overview of components that could be integrated to form an OREMS. Presented also is an OREMS that was developed by West Virginia University (WVU) to record in-use, brake-specific emissions from heavy-duty diesel-powered vehicles. Dubbed the Mobile Emissions Measurement System, or MEMS, the unit is capable of reporting brake-specific mass emissions of CO₂ and NO_X over 30-second windows. The MEMS was developed as part of the work described by the Consent Decrees entered into by six heavy-duty diesel engine manufacturers and the United States (US) government. Measurements of brake-specific NO_x and CO₂ recorded by the MEMS over an FTP test were found to be within 5% when compared to laboratory measurements.