Effects of Boundary Parameters on the Work-Based Window (WBW) and Not-to-Exceed (NTE) In-Use Emissions Quantification Methods.

摘要

Heavy-duty diesel engines are subjected to in-use emissions testing using portable emissions measurement systems (PEMS) to demonstrate compliance with U.S. EPA emissions standards while the vehicle is performing its regular on-road duty-cycle. The current methodology used for analyzing in-use emissions in the United States is the Not-To-Exceed (NTE) method and in Europe the Work-Based-Window (WBW) method. The primary objective of this study is to identify the sensitivity of the control factors governing both in-use emissions quantification methods, and range of optimum boundary parameter settings to maximize the amount of data available for evaluation while reporting representative NOx emissions. A total of 6 datasets provided by different engine manufacturers were analyzed, comprising data from 2 pre-2010 and 4 post-2010 U.S.EPA emissions complaint engines.;The study found that the engines investigated had difficulties in continuously meeting the NTE operational characteristics during in-use emissions testing. One of the reason was that a large amount of test activity data was eliminated due to the thresholds defined by the NTE method. Contrary to the NTE method, the WBW method analyzes the entire range of engine operation by integrating the power produced by the engine during the test into multiple work-based windows. However, WBW method also eliminates a certain amount of data from evaluation when the minimum average window power is below the threshold prescribed by the European Union regulations.;A screening design approach was used to develop a fractional factorial test matrix that explored the interaction and combined effect of extended boundary parameters. The results showed lower window-averaged bsNO x emissions and a maximum number of valid windows for the WBW method when the boundary parameters were expanded to include reference work in the range of one to two times the work produced over an FTP cycle, exhaust gas temperature threshold in the range of 200°C to 225°C, and a minimum average power threshold between 15% to 22.5% of maximum engine power. For the NTE method, expanding the control area to 15% of the maximum torque and power threshold, while maintaining the speed threshold at the default set point and reducing the exhaust temperature threshold to 150°C, increased the number of NTE events and bsNOx emissions by 87% and 24%, respectively. For both the WBW and the NTE methods, bsNOx emissions of optimal boundary parameters for post-2010 MY engines were within the U.S.EPA 2010 emissions standards. It is important to mention that the results presented in this study are valid only for operational characteristics representative of dominant highway operation due to the limited availability of in-use datasets.