School of Environment, State Key Joint Laboratory of Environment Simulation and Pollution Control, Tsinghua University , Beijing 100084, China.
International Council on Clean Transportation Europe , Berlin 10178, Germany.
Environ Sci Technol. 2015 Dec 15;49(24):14409-15. doi: 10.1021/acs.est.5b04242. Epub 2015 Dec 1.
Controlling nitrogen oxides (NOx) emissions from diesel passenger cars during real-world driving is one of the major technical challenges facing diesel auto manufacturers. Three main technologies are available for this purpose: exhaust gas recirculation (EGR), lean-burn NOx traps (LNT), and selective catalytic reduction (SCR). Seventy-three Euro 6 diesel passenger cars (8 EGR only, 40 LNT, and 25 SCR) were tested on a chassis dynamometer over both the European type-approval cycle (NEDC, cold engine start) and the more realistic Worldwide harmonized light-duty test cycle (WLTC version 2.0, hot start) between 2012 and 2015. Most vehicles met the legislative limit of 0.08 g/km of NOx over NEDC (average emission factors by technology: EGR-only 0.07 g/km, LNT 0.04 g/km, and SCR 0.05 g/km), but the average emission factors rose dramatically over WLTC (EGR-only 0.17 g/km, LNT 0.21 g/km, and SCR 0.13 g/km). Five LNT-equipped vehicles exhibited very poor performance over the WLTC, emitting 7-15 times the regulated limit. These results illustrate how diesel NOx emissions are not properly controlled under the current, NEDC-based homologation framework. The upcoming real-driving emissions (RDE) regulation, which mandates an additional on-road emissions test for EU type approvals, could be a step in the right direction to address this problem.
控制柴油乘用车在实际行驶过程中的氮氧化物（NOx）排放是柴油汽车制造商面临的主要技术挑战之一。为此，有三种主要技术可用：废气再循环（EGR）、稀燃 NOx 捕集器（LNT）和选择性催化还原（SCR）。2012 年至 2015 年期间，73 辆符合欧 6 标准的柴油乘用车（8 辆仅采用 EGR，40 辆采用 LNT，25 辆采用 SCR）在底盘测功机上进行了测试，测试包括欧洲型式认证循环（NEDC，冷机启动）和更现实的全球轻型车测试循环（WLTC 版本 2.0，热机启动）。大多数车辆在 NEDC 下满足 0.08 克/公里的 NOx 排放标准（按技术划分的平均排放因子：仅 EGR 为 0.07 克/公里，LNT 为 0.04 克/公里，SCR 为 0.05 克/公里），但在 WLTC 下，平均排放因子大幅上升（仅 EGR 为 0.17 克/公里，LNT 为 0.21 克/公里，SCR 为 0.13 克/公里）。五辆配备 LNT 的车辆在 WLTC 下表现非常差，排放量是规定限值的 7-15 倍。这些结果表明，在当前基于 NEDC 的认证框架下，柴油 NOx 排放并未得到有效控制。即将出台的实际行驶排放（RDE）法规要求对欧盟型式认证进行额外的道路排放测试，这可能是解决这一问题的正确方向。
