Ignition Delay Measurements of Four Component Model Gasolines Exploring the Impacts of Biofuels and Aromatics

The effect of combinations of biofuel (ethanol, isobutanol and 2-methyl furan) and aromatic (toluene) compounds in a four-component fuel blend, at fixed research octane number (RON) on ignition delay measured in an advanced fuel ignition delay analyzer (AFIDA 2805) was studied. Ignition delay measurements were performed at temperature range of 400-725 °C (673-998 K) and two chamber pressures of 10 and 20 bar. The ignition delay measurements show that at increasing aromatic and biofuel concentrations, the two-stage ignition behavior was suppressed, at both initial chamber pressures. Both RON 100 (isooctane) and RON 90 reference fuels showed two-stage ignition behavior, as did fuel mixtures with low biofuel and aromatic content. RON 90 fuels showed stronger two-stage ignition behavior than RON 100 fuels, as expected. Depending on the type of biofuel in the mixture, the ignition delay at low chamber temperatures could be greater than for the reference fuels. In particular, for the RON 100 mixtures at either 10 or 20 bar initial chamber pressure, the ignition delay at 400 °C (673 K) for the high-level blend of 2-methyl furan and toluene (30 vol% of each) exhibited an ignition delay that was 10 times longer than for neat isooctane. The results show the strong non-linear octane blending response of these three biofuel compounds, together with the kinetic antagonism that toluene displays in mixtures with isooctane. These results have implications for the formulation of biofuel mixtures for spark ignition and advanced compression ignition engines, where the non-linear octane blending response could be used to improve knock resistance or modulate the autoignition process.