Understanding of the octane response of gasoline/MTBE blends

Despite the wide utilization of MTBE as an octane booster for market gasoline fuels, the blending characteristics of methyl tert-butyl ether (MTBE) with gasoline fuels are not fully understood. This arises from the lack of octane number measurement of MTBE/gasoline blends, along with lack of detailed analyses of MTBE blending characteristics. In an attempt to address the knowledge gap in MTBE blending, this study provides new research octane number (RON) and motor octane number (MON) measurements of MTBE blended with various pure components and gasoline fuels. The first set of blends were binary mixtures of pure components blended with MTBE. The pure components we chosen to represent PIONA (paraffins, iso-paraffins, olefins, naphthenes and aromatics) molecular classes. The second set of blends were Fuels for Advanced Combustion Engines (FACE) and market gasoline fuels with MTBE. It was observed that the addition of MTBE to n-paraffins, iso-paraffins and olefins results in synergistic octane number effect while linear-by-volume and antagonistic blending was observed for MTBE blends with naphthenes and aromatics, respectively. The octane numbers and response of gasoline/MTBE blends are also dependent on the composition of the base gasoline fuel. These new measurements along with literature dataset were utilized to develop octane predictive models for MTBE blended with gasoline fuels. Various blending rules such as linear-by-volume (LBV), octane sensitivity (OS) and PIONA based models were developed in this work. The most accurate model was the linear-by-volume with the iso-paraffins and aromatics terms where more than 80% of the predictions are within the experimental reproducibility limits. The model can be used to predict and quantify the characteristics of octane boost caused by MTBE addition to gasoline fuels. It can also be used to optimize the octane boost due to the addition of MTBE by changing the composition of the base gasoline fuel.