This content is not included in your SAE MOBILUS subscription, or you are not logged in.
How well can mPEMS measure gas phase motor vehicle exhaust emissions?
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on April 14, 2020 by SAE International in United States
“Real world emissions” is an emerging area of focus in motor vehicle related air quality. These emissions are commonly recorded using portable emissions measurement systems (PEMS) designed for regulatory application, which are large, complex and costly. Miniature PEMS (mPEMS) is a developing technology that can significantly simplify on-board emissions measurement and potentially promote widespread use. Whereas full PEMS use analyzers to record NOx, CO, and HCs similar to those in emissions laboratories, mPEMS tend to use electrochemical sensors and compact spectroscopic detectors for their small size and low cost. The present work evaluates this approach by comparing measurements of NOx, CO, CO2 and HC emissions from five commercial mPEMS to both laboratory and full regulatory PEMS measurements. It further examines the use of vehicle on-board diagnostics data to calculate exhaust flow, as an alternative to on-vehicle exhaust flow measurement. The evaluations include two vehicle types, gasoline direct injection and diesel, and employ the US EPA and Worldwide Harmonized Light duty drive cycles. The results show that two classes of electrochemical NOx sensors are capable of providing high quality, second-by-second emissions data. One of these is ammonia sensitive, thus alternatively functioning as an effective NOx + NH3 sensor. Accurate measurement of CO and CO2 are also possible, but are limited in some specific cases by a long time response. HC measurement at present is only semi-quantitative and has a limit of detection well above the range of concentrations observed during normal vehicle operation. The mPEMS NOx and CO capabilities are sufficiently comparable to laboratory instruments that they should provide useful tools to investigate real world emissions behavior of motor vehicles.