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dc.contributor.advisorJohn B. Heywood.en_US
dc.contributor.authorJo, Young Suken_US
dc.contributor.otherMassachusetts Institute of Technology. Department of Mechanical Engineering.en_US
dc.date.accessioned2016-09-13T19:16:54Z
dc.date.available2016-09-13T19:16:54Z
dc.date.copyright2016en_US
dc.date.issued2016en_US
dc.identifier.urihttp://hdl.handle.net/1721.1/104246
dc.descriptionThesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.en_US
dc.descriptionCataloged from PDF version of thesis.en_US
dc.descriptionIncludes bibliographical references (pages [146]-151).en_US
dc.description.abstractTurbocharging, increasing the compression ratio, and downsizing a spark-ignition engine are well known strategies for improving vehicle fuel economy. However, such strategies result in higher in-cylinder pressures and temperatures which increase the likelihood of engine knock above that of naturally-aspirated engines. A high octane fuel, such as E85, effectively suppresses knock but the octane ratings of such fuels are much above what is required under normal driving conditions. To address this issue, there have been attempts to use octane more effectively by means of Octane on Demand (OOD): higher octane fuel is used only when needed. Engine experiments were performed to understand the combustion characteristics and knock limits of a commercially available turbocharged spark ignition engine. By utilizing data from engine experiments and engine-in-vehicle simulations, this study quantifies the octane requirement of a 2-liter turbocharged engine over its operating range as well as for various driving cycles. The average octane ratings of fuel needed in real-world driving were in the 60-80 RON range (maximum RON required around 90-100.) Engine configurations (boost/downsizing level, compression ratio), spark retard strategies, and vehicle configurations (vehicle type and loading conditions) were important parameters deciding these octane requirements. To analyze the effects of downsizing, retarding spark timing, increasing compression ratio, and vehicle type on dual fuel applications, GT-power simulation was conducted along with engine experiments and engine-in-vehicle simulations for a passenger vehicle and a medium-duty truck. Parametric studies were conducted to analyze the effects of listed variables on the vehicle fuel consumption, ethanol usage, and average engine efficiency. Downsizing a naturally-aspirated engine by 50% resulted in about a 30% increase in fuel economy. Ethanol consumption varied from 5 to 40% (by volume) of the total fuel used, depending on the details. Moderate amounts of spark retard reduced ethanol consumption by half while not deteriorating fuel economy significantly. Increasing compression ratio above 11.5 had a marginal return in fuel economy while demanding a significantly larger amount of ethanol. Finally, two dual fuel systems (twotank and on-board fuel separation) were modeled to compare benefits and disadvantages. Additionally, a new cycle-by-cycle pressure analysis method is presented, which help better explain the cycle-by-cycle variations of the spark ignition engine combustion process.en_US
dc.description.statementofresponsibilityby Young Suk Jo.en_US
dc.format.extent168 pagesen_US
dc.language.isoengen_US
dc.publisherMassachusetts Institute of Technologyen_US
dc.rightsM.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.en_US
dc.rights.urihttp://dspace.mit.edu/handle/1721.1/7582en_US
dc.subjectMechanical Engineering.en_US
dc.titleMore effective use of fuel octane in a turbocharged gasoline engine : combustion, knock, vehicle impactsen_US
dc.typeThesisen_US
dc.description.degreePh. D.en_US
dc.contributor.departmentMassachusetts Institute of Technology. Department of Mechanical Engineering
dc.identifier.oclc958144231en_US


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