From the AMERICAN CHEMICAL SOCIETY
Auto industry experts predict that more than 50 percent of cars on the road by 2020 will use a relatively new type of fuel-efficient engine. This transition, however, has raised questions about its ultimate effect on the climate. A study published in ACS’ journal Environmental Science & Technology has found that because the newer engines emit higher levels of the climate-warming pollutant black carbon than traditional engines, their impact on the climate is uncertain.
Naomi Zimmerman and colleagues analyzed four scenarios based on reported black carbon emissions from both traditional port fuel injection engines and newer gasoline direct injection (GDI) engines. They determined that installing efficient particulate filters in vehicles with GDI engines — even if they slightly lower fuel efficiency — could likely balance this trade-off and benefit the climate. But this outcome is not a given and depends on a variety of factors that can impact black carbon emissions such as engine design, fuel composition and geographic location.
Assessing the Climate Trade-Offs of Gasoline Direct Injection Engines
Naomi Zimmerman, Jonathan M. Wang, Cheol-Heon Jeong, James S. Wallace, and Greg J. Evans
Compared to port fuel injection (PFI) engine exhaust, gasoline direct injection (GDI) engine exhaust has higher emissions of black carbon (BC), a climate-warming pollutant. However, the relative increase in BC emissions and climate trade-offs of replacing PFI vehicles with more fuel efficient GDI vehicles remain uncertain. In this study, BC emissions from GDI and PFI vehicles were compiled and BC emissions scenarios were developed to evaluate the climate impact of GDI vehicles using global warming potential (GWP) and global temperature potential (GTP) metrics. From a 20 year time horizon GWP analysis, average fuel economy improvements ranging from 0.14 to 14% with GDI vehicles are required to offset BC-induced warming. For all but the lowest BC scenario, installing a gasoline particulate filter with an 80% BC removal efficiency and <1% fuel penalty is climate beneficial. From the GTP-based analysis, it was also determined that GDI vehicles are climate beneficial within <1–20 years; longer time horizons were associated with higher BC scenarios. The GDI BC emissions spanned 2 orders of magnitude and varied by ambient temperature, engine operation, and fuel composition. More work is needed to understand BC formation mechanisms in GDI engines to ensure that the climate impacts of this engine technology are minimal.