Abstract
As the fuel economy regulations increase in stringency, many manufacturers are implementing start-stop operation to enhance vehicle fuel economy. During start-stop operation, the engine shuts off when the vehicle is stationary for more than a few seconds. When the brake is released by the driver, the engine restarts. Depending on traffic conditions, start-stop operation can result in fuel savings from a few percent to close to 10%. Gasoline direct injection (GDI) engines are also increasingly available on light-duty vehicles. While GDI engines offer fuel economy advantages over port fuel injected (PFI) engines, they also tend to have higher PM emissions, particularly during start-up transients. Thus, there is interest in evaluating the effect of start-stop operation on PM emissions. In this study, a 2.5L GDI vehicle was operated over the FTP75 drive cycle. Runs containing cold starts (FTP-75 cycle Phases 1 & 2) and multiple runs containing hot starts (FTP-75 cycle Phases 3 & 4) were performed each day. Note that the FTP-75 Phases 3 & 4 are identical to Phases 1 & 2 except that the engine is warmed up. Three fuels were evaluated: an 87 AKI gasoline (E0), a 21% splash blend of ethanol and the 87 AKI gasoline (E21), and a 12% splash blend of iso-butanol and the 87 AKI gasoline (iBu12). PM mass, transient particle number concentration and size distribution, and soot mass concentration were evaluated for both start-stop operation and no start-stop operation on each fuel. Three Phase 1 & 2 cycles and as many as 27 Phase 3 & 4 cycles were performed for each fuel-mode combination. Composite FTP mass emissions for E0 and iBu12 showed increased total PM emissions with start-stop operation, but E21 showed no difference. Statistical analysis of the effects of start-stop on PM number and soot emissions showed different trends for different fuels. For example, when E0 is used with start-stop operation, the particle number decreased but the soot mass tended to increase. The results of this study have implications for hybrid vehicle operation as well because the internal combustion engine in hybrid vehicles must stop and re-start during normal operation.
Original language | English |
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Journal | SAE Technical Papers |
Volume | 2019-January |
Issue number | January |
DOIs | |
State | Published - Jan 15 2019 |
Event | SAE 2019 International Powertrains, Fuels and Lubricants Meeting, FFL 2019 - San Antonio, United States Duration: Jan 22 2019 → Jan 24 2019 |
Funding
This manuscript has been authored by UT-Battelle, LLC, under Contract No. DE-AC0500OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for the United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ).