The effectiveness of iso-alcohols in reducing vapor pressure and enhancing fuel properties of ethanol-gasoline mixtures

Ethanol, with its high octane rating and emissions advantages, is a viable and renewable alternative to gasoline for Spark-Ignition (SI) engines. However, when mixed with gasoline, ethanol forms an azeotropic mixture that increases the fuel's vapor pressure, potentially causing a clogged fuel line, engine stalling, and unstable operation. This study aimed to address the high vapor pressure challenge by adding C3, C4, and C5 iso-alcohols, namely, isopropanol (IP), isobutanol (IB), and isoamyl alcohol (IA), to reduce the vapor pressure of ethanol-gasoline blends. Fuel properties, including Reid vapor pressure (RVP), density, and distillation temperatures, were measured after each iso-alcohol was individually added to ethanol-gasoline blends (E10, E20, and E30) at a 5% volumetric ratio. According to the findings, E10 and E20 behaved as an azeotropic mixture, yielding increased vapor pressure. The highest RVP of 63.2 kPa was measured for E10. However, adding IP, IB, and IA alcohols to E10 reduced the RVP to 61.8 kPa, 61.3 kPa, and 61.1 kPa, respectively. Including iso-alcohols also increased the density of ethanol-gasoline blends, with the highest density of 763.6 kg/m³ was measured for E30+IA5. Furthermore, adding iso-alcohols improved the distillation profiles, octane rating, and heating value of the ethanol-gasoline blends. More importantly, it was found that the measured fuel properties met the requirements of the European Standards for Gasoline (EN 228) except for some gasoline samples' distilled values for E70 and E100. Based on the findings, C3-C5 iso-alcohols effectively reduce the high vapor pressure associated with ethanol-gasoline azeotropic mixtures, allowing a higher volume of renewable ethanol blending.