New Analysis Methods Estimate a Critical Property of Ethanol Fuel Blends

Kathryn Ruckman

Research output: NRELFact Sheet


To date there have been no adequate methods for measuring the heat of vaporization of complex mixtures. This research developed two separate methods for measuring this key property of ethanol and gasoline blends, including the ability to estimate heat of vaporization at multiple temperatures. Methods for determining heat of vaporization of gasoline-ethanol blends by calculation from a compositional analysis and by direct calorimetric measurement were developed. Direct measurement produced values for pure compounds in good agreement with literature. A range of hydrocarbon gasolines were shown to have heat of vaporization of 325 kJ/kg to 375 kJ/kg. The effect of adding ethanol at 10 vol percent to 50 vol percent was significantly larger than the variation between hydrocarbon gasolines (E50 blends at 650 kJ/kg to 700 kJ/kg). The development of these new and accurate methods allows researchers to begin to both quantify the effect of fuel evaporative cooling on knock resistance, and exploit this effect for combustion of hydrocarbon-ethanol fuel blends in high-efficiency SI engines.
Original languageAmerican English
StatePublished - 2016

NREL Publication Number

  • NREL/FS-5400-65806


  • ethanol
  • fuels
  • heat of vaporization
  • HOV
  • octane
  • spark-ignition engines


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