Alcohol–Additive Ternary Mixtures for Sustainable Fuel Formulations: Experimental Excess Molar Enthalpy and Thermodynamic Modeling

Abstract Fuel blends incorporating oxygenated additives are increasingly explored to enhance combustion efficiency and reduce greenhouse gas emissions. Understanding the thermodynamic behavior of such mixtures is essential for optimizing their formulation. In this study, the excess molar enthalpy ( $${H}_{m}^{E}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>H</mml:mi> <mml:mrow> <mml:mi>m</mml:mi> </mml:mrow> <mml:mi>E</mml:mi> </mml:msubsup> </mml:math> ) a key property reflecting molecular interactions and non-ideality was measured for four ternary blends containing 2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)ethanol, 2-methoxyethanol, and 2-phenoxyethanol, each mixed with ethanol, at 298.15 and 313.15 K under 0.1 MPa using a quasi-isothermal flow calorimeter. The experimental results were correlated using the Redlich–Kister, NRTL, and UNIQUAC models, while the predictive performance of the Modified UNIFAC (Dortmund) model was also assessed. Positive $${H}_{m}^{E}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>H</mml:mi> <mml:mrow> <mml:mi>m</mml:mi> </mml:mrow> <mml:mi>E</mml:mi> </mml:msubsup> </mml:math> values were obtained for all mixtures, indicating endothermic mixing and dominant dispersive–dipolar interactions. Among the applied models, the Redlich–Kister equation provided the best correlation with experimental data. The results contribute valuable thermodynamic benchmarks for modeling the energetics of oxygenated fuel blends and improving predictive approaches for complex liquid mixtures.