In response to a National Academy of Sciences (NAS) report’s suggestion that more representative emissions data be used in the U.S. EPA’s mobile source emissions estimation tool (previously called MOBILE, now the Motor Vehicle Emissions Simulator, or MOVES), the agency’s Office of Transportation and Air Quality (OTAQ) has put a great deal of effort into developing and acquiring equipment capable of measuring in-use gaseous and particulate mass emissions. The data derived from measurements are envisioned to populate the emissions database of the MOVES model, and they will supplement data from dynamometer-based measurements of vehicle and engine emissions collected during driving cycles that have been the standard method of verifying compliance to federal emissions regulations.
In the MOBILE models, dynamometer emissions measurements collected over specific driving cycles have been used as a basis to estimate emissions inventories or the total pollutant emissions in a particular area due to the use of a given population of vehicles at a defined time and set of conditions. However, average or typical driving cycles do not necessarily give an accurate estimate of everyday vehicle use. Nor do they yield the typical power demands on the vehicle’s engine when run on a dynamometer. And, vehicle emissions are mainly dependent on the engine power demand and the efficiency of the emissions controls (catalytic converter, exhaust gas recirculation, etc.) installed on the vehicle. Both the accuracy of the emissions inventories and the determination of how well the vehicle or engine is keeping within the emissions regulations have been under review. The NAS’s report recommends that the EPA collect more real-world data to more accurately predict the effects of its emissions regulations.
To that end, the EPA has committed to developing and using portable emissions measurement systems (PEMS) for emissions regulatory and inventory work. The agency already has begun many campaigns to measure on-road vehicle emissions data. On the regulatory side the motivation has been via a federal court order, and an ensuing measurement allowance program for gaseous PEMS has been completed.
Currently, manufacturers of heavy-duty engines have begun taking on-road gaseous emissions data from on-highway vehicles for certification. On the particulate matter (PM) regulatory side, three time-resolved PM measurement instruments have been submitted in the PM measurement allowance program. Additionally, a nonroad vehicle regulatory program for construction equipment is being planned.
For the purpose of inventory development, the EPA has multiple programs completed, taking place, and in the planning stages that are in collaboration with other organizations and state governments. These inventory programs have started on a small scale with tens of vehicles in a limited geographical area and have grown to a larger scale that encompasses larger geographical areas. Light duty vehicles, city buses, heavy-duty trucks, and off-road construction vehicles have been outfitted with PEMS.
Researchers from the EPA, Eastern Research Group, and Sensors Inc. recently completed a project in the Kansas City area that used specially developed equipment to measure time resolved (1-hz) in-use gaseous emissions (CO2, CO, THC, NOx) and particulate matter mass (with Teflon membrane filter) emissions from 29 construction vehicles (model years ranging from 1993 to 2007) over a three-year period. Also measured were engine speed, and, in a few cases, engine power from the vehicle engine control module. From these exhaust and engine operation measurements pollutant mass emission rates, mass concentrations, mass per fuel use, and mass per energy (work or brake specific) emissions have been determined. The brake specific emissions were estimated from the engine speed measurements and brake specific fuel consumption curves. About 35 tests averaging 220 min were conducted.
This article is based on SAE technical paper 2010-01-1952 by Carl Fulper, Robert Giannelli, Constance Hart, David Hawkins, Jingnan Hu, and James Warila of the U.S. EPA’s Office of Transportation and Air Quality; Sandeep Kishan and Michael Sabisch of Eastern Research Group; and Paul Clark, Chris Darby, Carl Ensfield, Don Henry, Louis Moret, and Ron Tandy of Sensors Inc.