Abstract：
This research analyzed the real-world NOx and particle number (PN) emissions of 21 China VI heavy-duty diesel trucks (HDDTs). On-road emission conformity was first evaluated with portable emission measurement system (PEMS). Only 76.19 %, 71.43 % and 61.90 % of the vehicles passed the NOx test, PN test and both tests, respectively. The impacts of vehicle features including exhaust gas recirculation (EGR) equipment, mileage and tractive tonnage were then assessed. Results demonstrated that EGR helped reducing NOx emission factors (EFs) while increased PN EFs. Larger mileages and tractive tonnages corresponded to higher NOx and PN EFs, respectively. In-depth analyses regarding the influences of operating conditions on emissions were conducted with both numerical comparisons and statistical tests. Results proved that HDDTs generated higher NOx EFs under low speeds or large vehicle specific powers (VSPs), and higher PN EFs under high speeds or small VSPs in general. In addition, unqualified vehicles generated significantly higher NOx EFs than qualified vehicles on freeways or under speed≥40 km/h, while significant higher PN EFs were generated on suburban roads, freeways or under operating modes with positive VSPs by unqualified vehicles. The reliability and accuracy of on-board diagnostic (OBD) NOx data were finally investigated. Results revealed that 43 % of the test vehicles did not report reliable OBD data. Correlation analyses between OBD NOx and PEMS measurements further demonstrated that the consistency of instantaneous concentrations were generally low. However, sliding window averaged concentrations show better correlations, e.g., the Pearson correlation coefficients on 20s-window averaged concentrations exceeded 0.85 for most vehicles. The research results provide valuable insights into emission regulation, e.g., focusing more on medium- to high-speed operations to identify unqualified vehicles, setting higher standards to improve the quality of OBD data, and adopting window averaged OBD NOx concentrations in evaluating vehicle emission performance.
摘要：
这项研究分析了21辆中国VI重型柴油卡车（HDDT）的实际NOx和颗粒数（PN）排放。首先使用便携式排放测量系统（PEMS）评估道路排放符合性。只有76.19%，71.43%和61.90%的车辆通过NOx测试，PN测试和两个测试，分别。包括废气再循环（EGR）设备在内的车辆功能的影响，然后评估里程和牵引吨位。结果表明，EGR有助于降低NOx排放因子（EF），同时增加PNEF。较大的里程和牵引吨位对应较高的NOx和PNEF，分别。通过数值比较和统计测试，对操作条件对排放的影响进行了深入分析。结果证明，HDDT在低速或大车辆比功率（VSP）下产生较高的NOxEF，和更高的PNEF在高速或小VSP一般。此外,不合格车辆产生的NOxEF明显高于高速公路上或车速≥40km/h的合格车辆，虽然郊区道路上产生了显著较高的PNEF，高速公路或不合格车辆在具有正VSP的运行模式下。最后研究了车载诊断（OBD）NOx数据的可靠性和准确性。结果显示,43%的测试车辆没有报告可靠的OBD数据。OBDNOx和PEMS测量之间的相关性分析进一步证明瞬时浓度的一致性通常较低。然而,滑动窗口平均浓度显示出更好的相关性，例如，对于大多数车辆，20s窗口平均浓度的Pearson相关系数超过0.85。研究结果为排放管制提供了有价值的见解，例如，更加注重中高速运行，以识别不合格车辆，设定更高的标准以提高OBD数据的质量，并采用窗口平均OBDNOx浓度评价车辆排放性能。
