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Experimental Investigation of Spark-Ignited Combustion with High-Octane Biofuels and EGR. 1. Engine Load Range and Downsize Downspeed Opportunity

The present study experimentally investigates spark-ignited combustion with 87 AKI E0 gasoline in its neat form
and in midlevel alcohol−gasoline blends with 24% vol/vol isobutanol−gasoline (IB24) and 30% vol/vol ethanol−gasoline (E30).
A single-cylinder research engine was used with an 11.85:1 compression ratio, hydraulically actuated valves, laboratory intake air,
and was capable of external exhaust gas recirculation (EGR). Experiments were conducted with all fuels to full-load conditions
with λ = 1, using both 0% and 15% external cooled EGR. Higher octane number biofuel blends exhibited increased
stoichiometric torque capability at this compression ratio, where the unique properties of ethanol enabled a doubling of the
stoichiometric torque capability with E30 as compared to 87 AKI, up to 20 bar IMEPg (indicated mean effective pressure gross)
at λ = 1. EGR provided thermodynamic advantages and was a key enabler for increasing engine efficiency for all fuel types.
However, with E30, EGR was less useful for knock mitigation than gasoline or IB24. Torque densities with E30 with 15% EGR at
λ = 1 operation were similar or better than a modern EURO IV calibration turbo-diesel engine. The results of the present study
suggest that it could be possible to implement a 40% downsize + downspeed configuration (1.2 L engine) into a representative
midsize sedan. For example, for a midsize sedan at a 65 miles/h cruise, an estimated fuel consumption of 43.9 miles per gallon
(MPG) (engine out 102 g-CO2/km) could be achieved with similar reserve power to a 2.0 L engine with 87AKI (38.6 MPG,
engine out 135 g-CO2/km). Data suggest that, with midlevel alcohol−gasoline blends, engine and vehicle optimization can offset
the reduced fuel energy content of alcohol−gasoline blends and likely reduce vehicle fuel consumption and tailpipe CO2 emissions.

Derek Splitter
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.