Investigation of Knock limited Compression Ratio of Ethanol Gasoline Blends

Conference · Fri Jan 01 04:00:00 EST 2010

DOI:https://doi.org/10.4271/2010-01-0619· OSTI ID:976034

Szybist, James P ^[1]; Youngquist, Adam D ^[1]; Wagner, Robert M ^[1]; Moore, Wayne ^[2]; Foster, Matthew ^[2]; Confer, Keith ^[2]

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1. ORNL
2. Delphi

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 conditions to determine the knock limited compression ratio (CR) of ethanol fuel blends. The geometric compression ratio is varied by changing pistons, producing CR from 9.2 to 13.66. 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. It was found that at substantially similar engine conditions, increasing the ethanol content of the fuel results in higher engine efficiency and higher engine power. These can be partially attributed to a charge cooling effect and a higher heating valve of a stoichiometric mixture for ethanol blends (per unit mass of air). Additional thermodynamic effects on and a mole multiplier are also explored. It was also found that high CR can increase the efficiency of ethanol fuel blends, and as a result, the fuel economy penalty associated with the lower energy content of E85 can be reduced by about a third. Such operation necessitates that the engine be operated in a de-rated manner for gasoline, which is knock-prone at these high CR, in order to maintain compatibility. By using EIVC and LIVC strategies, good efficiency is maintained with gasoline, but power is reduced by about 34%.

• Research Organization: Oak Ridge National Laboratory (ORNL); Fuels, Engines and Emissions Research Center; National Transportation Research Center
• Sponsoring Organization: EE USDOE - Office of Energy Efficiency and Renewable Energy (EE)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 976034
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
10 SYNTHETIC FUELS
33 ADVANCED PROPULSION SYSTEMS
AIR
ANTIKNOCK RATINGS
COMPATIBILITY
COMPRESSION RATIO
EFFICIENCY
ENGINES
ETHANOL
ETHANOL FUELS
Ethanol
FUEL CONSUMPTION
GASOLINE
HEATING
HVA
HYDRAULICS
MIXTURES
PISTONS
POWER DENSITY
THERMODYNAMICS
VALVES
VAPORIZATION HEAT
VVA
efficiency
variable valve actuation