Simulation of phase equilibria properties of fuels and blends of fuels with oxygenated compounds

Abstract

Non-ideality in fuel-biofuel blends arises from the presence of oxygenated compounds in a non-polar substrate, significantly impacs on phase behavior and, consequently, fuel storage and transport, and engine performance. Volatility properties, which are key indicators of fuel quality, are regulated by standards and evaluated through standardized tests. This work explores the phase equilibrium of fuel-oxygenate blends using a predictive thermodynamic model and propose novel calculation methods to simulate volatility tests, including Reid Vapor Pressure, vapor lock protection temperature, and the distillation curve. Additionally, water tolerance in oxygenate/gasoline blends is predicted using a robust liquid–liquid equilibrium approach. The Group Contribution with Association Equation of State (GCA-EOS) model accurately captures the phase behavior across a wide range of biofuels, including advanced candidates such as 2-methyltetrahydrofuran and ethyl levulinate. The proposed models showed good predictive accuracy, with average relative deviations of 1,4% in distillation temperatures and average absolute deviations of 1.1 kPa for Reid vapor pressure. In liquid–liquid equilibrium calculations, the average absolute error was 0.02 for oxygenate partition coefficients and 0.37 for water. The proposed methodology enhances understanding of oxygenate effects in blends and provides predictive tools for fuel blend design, aiming to reduce the exploratory experimental work.