Comprehensive US database and model for ethanol blend effects on regulated tailpipe emissions.

Area of Science:

• Environmental Science
• Chemical Engineering
• Automotive Engineering

Background:

• Gasoline exhaust emissions, including particulate matter (PM), oxides of nitrogen (NOx), carbon monoxide (CO), and total hydrocarbons (THC), significantly impact air quality and human health.
• Ethanol, a renewable fuel additive, is blended into gasoline for its anti-knock properties, altering fuel composition and potentially influencing emissions.
• Existing research on ethanol's effect on vehicle emissions often uses non-market fuel blends or limited data, hindering accurate real-world emissions inventory estimations.

Purpose of the Study:

• To assess the real-world implications of ethanol blending on regulated gasoline exhaust emissions (PM, NOx, CO, THC).
• To develop regression models predicting emission differences based on fuel and vehicle properties for market fuel compositions.
• To account for nonlinear blending effects by modeling both low (up to 10%) and mid-level ethanol blends.

Main Methods:

• Compiled a comprehensive database of US vehicle emission studies.
• Developed regression models incorporating fuel and vehicle characteristics to estimate emissions from market fuel blends.
• Utilized Federal Test Procedure (FTP) and Unified Cycle (LA92) driving data, analyzing cold-start and hot-running emissions.
• Modeled low and mid-level ethanol blends separately to address nonlinear responses.

Main Results:

• Particulate matter (PM) cold-start emissions were lower with higher ethanol content, particularly at higher blend levels.
• Hot-running emissions showed no significant difference related to ethanol content.
• Emission effects varied between port fuel injection (PFI) and gasoline direct injection (GDI) vehicles.
• NOx, CO, and THC results differed between comprehensive and split (low/mid blend) models.
• CO emissions generally decreased with higher ethanol content in PFI vehicles and hot-running GDI vehicles.
• NOx results showed variability across blend levels, while THC results were scattered at higher blends.

Conclusions:

• Vehicle emissions inventories should differentiate between PFI and GDI engines due to distinct responses to ethanol blending.
• The study provides a method for estimating real-world emissions impacts of ethanol-gasoline blends, despite inherent uncertainties in data and modeling.
• Findings highlight the need for careful consideration of fuel blend composition and vehicle technology when assessing environmental impacts.