Department of Mechanical Engineering, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States.
College of Engineering, University of Georgia , Athens, Georgia 30602, United States.
Environ Sci Technol. 2017 Jun 6;51(11):6542-6552. doi: 10.1021/acs.est.6b06509. Epub 2017 May 9.
Recent increases in the Corporate Average Fuel Economy standards have led to widespread adoption of vehicles equipped with gasoline direct-injection (GDI) engines. Changes in engine technologies can alter emissions. To quantify these effects, we measured gas- and particle-phase emissions from 82 light-duty gasoline vehicles recruited from the California in-use fleet tested on a chassis dynamometer using the cold-start unified cycle. The fleet included 15 GDI vehicles, including 8 GDIs certified to the most-stringent emissions standard, superultra-low-emission vehicles (SULEV). We quantified the effects of engine technology, emission certification standards, and cold-start on emissions. For vehicles certified to the same emissions standard, there is no statistical difference of regulated gas-phase pollutant emissions between PFIs and GDIs. However, GDIs had, on average, a factor of 2 higher particulate matter (PM) mass emissions than PFIs due to higher elemental carbon (EC) emissions. SULEV certified GDIs have a factor of 2 lower PM mass emissions than GDIs certified as ultralow-emission vehicles (3.0 ± 1.1 versus 6.3 ± 1.1 mg/mi), suggesting improvements in engine design and calibration. Comprehensive organic speciation revealed no statistically significant differences in the composition of the volatile organic compounds emissions between PFI and GDIs, including benzene, toluene, ethylbenzene, and xylenes (BTEX). Therefore, the secondary organic aerosol and ozone formation potential of the exhaust does not depend on engine technology. Cold-start contributes a larger fraction of the total unified cycle emissions for vehicles meeting more-stringent emission standards. Organic gas emissions were the most sensitive to cold-start compared to the other pollutants tested here. There were no statistically significant differences in the effects of cold-start on GDIs and PFIs. For our test fleet, the measured 14.5% decrease in CO emissions from GDIs was much greater than the potential climate forcing associated with higher black carbon emissions. Thus, switching from PFI to GDI vehicles will likely lead to a reduction in net global warming.
最近，企业平均燃油经济性标准的提高导致了广泛采用配备汽油直喷（GDI）发动机的车辆。发动机技术的变化会改变排放物。为了量化这些影响，我们从加利福尼亚州在用车辆中招募了 82 辆轻型汽油车，在底盘测功机上使用冷启动统一循环进行测试，测量了这些车辆的气相和颗粒相排放物。该车队包括 15 辆 GDI 车辆，其中 8 辆 GDI 车辆经过认证，达到了最严格的排放标准，即超低排放车辆（SULEV）。我们量化了发动机技术、排放认证标准和冷启动对排放的影响。对于经过相同排放标准认证的车辆，PFI 和 GDI 之间的规定气相污染物排放量没有统计学差异。然而，由于元素碳（EC）排放量较高，GDI 的颗粒物（PM）质量排放量平均比 PFI 高 2 倍。与超低排放车辆（3.0±1.1 毫克/英里）相比，SULEV 认证的 GDI 的 PM 质量排放量低 2 倍，这表明发动机设计和校准有所改进。综合有机物质谱分析表明，PFI 和 GDI 之间挥发性有机化合物排放物的组成，包括苯、甲苯、乙苯和二甲苯（BTEX），没有统计学上的显著差异。因此，排气中的二次有机气溶胶和臭氧形成潜力不取决于发动机技术。对于符合更严格排放标准的车辆，冷启动对总统一循环排放量的贡献更大。与这里测试的其他污染物相比，有机气体排放对冷启动的敏感性最高。冷启动对 GDI 和 PFI 的影响没有统计学上的显著差异。对于我们的测试车队，与 GDI 车辆相比，CO 排放量减少了 14.5%，这与更高的黑碳排放量相关的潜在气候强迫作用相比要大得多。因此，从 PFI 切换到 GDI 车辆可能会导致净全球变暖减少。
