Heat of Vaporization and Species Evolution during Gasoline Evaporation Measured by DSC/TGA/MS for Blends of C1 to C4 Alcohols in Commercial Gasoline Blendstocks

摘要

Evaporative cooling of the fuel-air charge by fuel evaporation is an important feature of direct-injection spark-ignition engines that improves fuel knock resistance and reduces pumping losses at intermediate load, but in some cases, may increase fine particle emissions. We have reported on experimental approaches for measuring both total heat of vaporization and examination of the evaporative heat effect as a function of fraction evaporated for gasolines and ethanol blends. In this paper, we extend this work to include other low-molecular-weight alcohols and present results on species evolution during fuel evaporation by coupling a mass spectrometer to our differential scanning calorimetry/thermogravimetric analysis instrument. The alcohols examined were methanol, ethanol, 1-propanol, isopropanol, 2-butanol, and isobutanol at 10 volume percent, 20 volume percent, and 30 volume percent. The results show that total heat of vaporization of the alcohol gasoline blends is in line with the decreasing heat of vaporization in kilojoules per kilogram with increasing alcohol carbon number, as expected. Mass spectrometer results show that methanol fully evaporates at significantly lower fraction evaporated relative to other alcohols even though it is present at higher molar concentration at a fixed volumetric concentration. Certain alcohols, especially methanol and ethanol, can suppress the evaporation of aromatic compounds such as cumene during the evaporation process in some samples. While the use of mass spectrometry to analyze the composition of the evolving gas mixture provided useful results for a relatively simple research gasoline (FACE B), additional research is required to practically apply this methodology to more complex commercial gasolines.