Evaluation of an On-board, Real-time Electronic Particulate Matter Sensor Using Heavy-duty On-highway Diesel Engine Platform 2020-01-0385
California Air Resources Board (CARB) has instituted requirements for on-board diagnostics (OBD) that makes a spark-plug sized particulate matter (PM) sensor a critical component of the OBD system to detect diesel particulate filter (DPF) failure. Current PM OBD thresholds for heavy-duty on-highway vehicles is 0.03 g/hp-hr and for light-duty vehicles (2019+ Model Year LEV III) is 17.5 mg/mile. To meet these regulations, and more stringent future regulations, real-time PM sensors offer numerous benefits over traditional accumulation type resistive sensors. The focus of this work is on the experimental evaluation of such a real-time PM sensing technology manufactured by CoorsTek LLC. A 2011 model year on-highway heavy-duty diesel engine fitted with diesel oxidation catalyst/diesel particulate filter/selective catalytic reducer/ammonia oxidation catalyst (DOC/DPF/SCR/AMOX) was used for the evaluation program. Sensors were tested at an emission level of ~ 0.02 g/hp-hr using five repeats each of Federal Test Procedure (FTP), Non-road transient cycle (NRTC), world harmonized transient cycle (WHTC) and ramped modal cycle (RMC) drive cycles. Exhaust emission levels were tuned using a bypass DOC flow path fitted in parallel to the stock aftertreatment system. Eight sensors were benchmarked against state-of-the-art laboratory particle instrumentation that served as references. An AVL micro-soot sensor (MSS) was used for real-time soot mass measurement and a TSI engine exhaust particle sizer (EEPS) coupled with SwRI’s solid particle sampling system (SPSS) was used for real-time solid particle number and size measurement. Additionally, CFR Part 1065 compliant PM filter measurements were performed from full flow constant volume sampling (CVS) tunnel. Performance of sensors was compared with that of reference instrumentation to examine their accuracy and variability on 1. Concentration basis, 2. Flux basis and 3. Brake specific emission basis. Transient cycles were analyzed over multiple window lengths ranging from 100 seconds to the entire cycle length. Relationships between sensors and reference instrumentation for each window was analyzed. Sensor to sensor variability along with sensor response to each drive cycle was studied. Further, sensor response was studied on a global basis with disregard to drive cycle.
Currently, accumulation-type PM sensors that are not real-time are widely used in the market place due to the absence of commercially available real-time sensors. Results observed during these studies suggest that real-time sensing has tremendous potential to serve as exhaust emission monitors not only for DPF diagnostics, but also for real-time emissions control while installed at engine-out location.
Vinay Premnath, Imad Khalek, Patrick Thompson, Leta Woo
Southwest Research Institute, EmiSense Technologies LLC