Formulating gasoline surrogate for emulating octane blending properties with ethanol

This work develops a surrogate fuel that reproduces the octane blending of a market gasoline with ethanol. It first extends our previous investigation that reported strong, non-linear blending for ethanol/paraffin and ethanol/aromatic mixtures (Foong et al., Fuel 2014 p. 727) to consider mixtures of ethanol/cycloparaffin, ethanol/olefin, and hydrocarbons from different groups. On the molar basis, ethanol blends synergistically with cyclohexane and 1-hexene, whereas toluene blends antagonistically with ethanol and all hydrocarbons studied. Various alternative surrogate formulations are then considered given the observed inadequacy of toluene reference fuels (TRFs, mixtures of iso-octane, n-heptane, and toluene) in emulating the octane blending behaviours of a market gasoline with ethanol. These alternative surrogates are formulated to match the market gasoline's Research Octane Number (RON) and its major hydrocarbon group composition. The best performing surrogate, which contains 38% iso-pentane, 12% n-pentane, 30% 1,2,4-trimethylbenzene, 10% cyclohexane, and 10% 1-hexene (all by volume), reproduces the RONs of the market gasoline mixed with ethanol over the entire blending range within 0.5 octane number. This surrogate formulation demonstrates that iso-pentane, n-pentane and 1,2,4-trimethylbenzene are more suitable than TRF compounds for emulating the octane blending of the gasoline/ethanol mixtures used in this study. A RON correlation is then proposed for the developed gasoline surrogate, taking into account the observed, non-linear interactions of ethanol and individual hydrocarbon compounds, which accurately predicts the RON of the surrogate/ethanol mixtures.