Characterization of Exhaust Emissions in a SI Engine using E85 and Cooled EGR 2009-01-1952
Gasoline-ethanol blends are being used or have been considered as a fuel for spark ignition engines. The motivation for using the blends varies in indifferent parts of the world and even in regions within a country. The increasing cost of gasoline, combined with regional tax incentives, is one of the reasons for increased interests in gasoline-ethanol blends in recent years in the U.S. Many vehicular engines are not designed to use a specific gasoline-ethanol blend. Rather, the engines have multi-blend capability, ranging from E0 to about E85. It is plausible that engine-out emissions will vary depending on the blend being used which may be further impacted by the level of EGR used with the blends. The present work was carried out to investigate engine out emissions when a vehicular spark-ignition engine was operated on E0 and E85 and different levels of EGR.
A 4-cylinder, 2.5 liter, PFI engine was used in the experimental investigation. The engine was operated at 1500 and 2100 rpm and brake mean effective pressure of 1.5 bar or 3.5 bar. The engine was operated at stoichiometric air-to-fuel ratio at controlled operating parameters. The mixture stoichiometry was monitored by a wide-range oxygen sensor calibrated for the fuels used in the study. Exhaust samples were analyzed for different emissions species using a FT-IR analyzer. Overall, E85 blend produced slightly lower levels of NOx than E0 (pure gasoline) but the difference was more noticeable at higher load and high EGR rates. But E85 produced much higher concentrations of acetalydehydes in engine exhaust than the gasoline fuel. The difference was more pronounced at lower engine load. Addition of EGR increased aldehyde levels even further.
The coefficient of variation in indicated mean effective pressure increased with an increase in EGR rate. Not much difference in the coefficient of variation between E85 and E0 was observed at higher engine load but there was a significant difference when the engine was operating at 1500 rpm and lower load. Similar trend was observed at higher EGR rates when the engine was operating at 2100 rpm. Low speed operation, combined with high EGR rates, lowers overall temperatures in the combustion chamber which favors acetalydehyde emissions. Depending on operating conditions, it may be necessary to limit EGR rates to keep COV in imep within limits when the engine is operated on E85.