Measurement of Heat of Vaporization for Research Gasolines and Ethanol Blends by DSC/TGA
The heat of vaporization (HOV) is a relatively poorly studied fuel property that can be related to a fuel's evaporation characteristics and knock resistance and, therefore, the emissions and efficiency of direct-injection spark-ignition engines. Methods for measuring the HOV of complex gasoline mixtures and blends of gasoline with ethanol and other oxygenates require additional development. Recently, we described a differential scanning calorimetry/thermogravimetric (DSC/TGA) method to perform HOV measurements. Herein we describe a detailed investigation of factors affecting the precision and accuracy of the DSC/TGA method and examine enthalpy evolution and mass loss rate for research gasolines as a function of fraction evaporated. Examination of n-hexane evaporation using several DSC/TGA pan/lid configurations showed that initial sample loss can be reduced using a well-fitting pinhole lid on the sample pan, which reduces the evaporation rate during the balance of the experiment. However, additional experiments with research gasolines revealed that tight lid placement on the pans is not always achieved. Nevertheless, accurate total HOV measurements, with less than 10% initial sample loss, could be achieved for low volatility gasolines regardless of lid placement. A higher mass loss might be expected for higher vapor pressure (wintertime) gasolines. Because of variations in pan lids and their placement and their significant impact on results, quantitative comparisons between different samples of mass loss rate and heat flow curves versus time or fraction evaporated are not yet possible. However, features in the mass loss rate and heat flow curves are reproducible. Furthermore, results show that ethanol-gasoline blend evaporation is highly influenced by the formation of near-azeotropic mixtures of ethanol and specific gasoline components, causing a flattening of the mass and heat curves, with a sharp evaporation rate reduction after the ethanol is evaporated.
- Research Organization:
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (EE-3V)
- Grant/Contract Number:
- AC36-08GO28308
- OSTI ID:
- 1484590
- Report Number(s):
- NREL/JA-5400-70435
- Journal Information:
- Energy and Fuels, Vol. 32, Issue 12; ISSN 0887-0624
- Publisher:
- American Chemical Society (ACS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
Similar Records
Reducing Sample Loss in Measurement of Heat of Vaporization of Ethanol/Gasoline Blends by Differential Scanning Calorimetry/Thermogravimetric Analysis
Heat of Vaporization and Species Evolution Suring Gasoline Evaporation Measured by DSC/TGA/MS for Blends of C1 to C4 Alcohols in Commercial Gasoline Blendstocks