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Investigation of Knock Limited Compression Ratio of Ethanol Gasoline Blends

Ethanol offers significant potential for increasing the
compression ratio of SI engines resulting from its high octane
number and high latent heat of vaporization. A study was
conducted to determine the knock limited compression ratio
of ethanol - gasoline blends to identify the potential for
improved operating efficiency. To operate an SI engine in a
flex fuel vehicle requires operating strategies that allow
operation on a broad range of fuels from gasoline to E85.
Since gasoline or low ethanol blend operation is inherently
limited by knock at high loads, strategies must be identified
which allow operation on these fuels with minimal fuel
economy or power density tradeoffs.
A single cylinder direct injection spark ignited engine with
fully variable hydraulic valve actuation (HVA) is operated at
WOT and other high-load conditions to determine the knock
limited compression ratio (CR) of ethanol fuel blends. The
geometric CR is varied by changing pistons, producing CR
from 9.2 to 12.87. The effective CR is varied using an
electro-hydraulic valvetrain that changed the effective
trapped displacement using both Early Intake Valve Closing
(EIVC) and Late Intake Valve Closing (LIVC). The EIVC
and LIVC strategies result in effective CR being reduced
while maintaining the geometric expansion ratio.

James Szybist
Contact Person
Tim Theiss
Contact Organization
Oak Ridge National Laboratory
Contact Email
Bioenergy Category
Publication Year
Funded from the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Bioenergy Technologies Office.