Hot Surface Ignition of Gasoline-Ethanol Fuel Mixtures

With the increased consumer interest in ethanol-based fuels as a measure of reducing the United States dependence on foreign oil, the use of E85 and other ethanol/petroleum fuel blends is on the increase. While some autoignition data for summer and winter blends of gasoline on hot surfaces exist beyond the standard ASTM E659-78 test procedure [ 1 ], there is little data on ethanol-based fuels and their HSI characteristics.

All these factors (and more) play a role in influencing HSI: the molecular structure of the fuel, the surface material temperature, the surface geometry of the material, the material properties of the hot surface, the fluid flow rate, the contact time, and environmental factors such as air flow in the immediate area of the fuel contact. This paper focuses specifically on the various blends of ethanol along with commercially available fuels tested for HSI in a controlled laboratory environment, where the temperature was varied but other influences were attempted to be held constant. The fuels tested were commercially available unleaded regular gasoline (CA ULR), commercially available E85 (CA E85), certification grade gasoline (indolene) and blends of indolene and ethanol. The HSI temperatures of each of the fuel blends determined by laboratory experimentation are compared to the autoignition temperatures obtained through ASTM E659-78 test methodology. More than 1300 data points were collected.

The results depict a range of temperatures between levels at which HSI was not observed in any samples to where HSI was observed 100% of the time, for each type of fuel tested. The testing showed that as the level of ethanol increased beyond 10%, temperatures for observed HSI events tended to decrease and stabilized around 75% ethanol concentration, although the ASTM-AIT temperatures remained relatively constant throughout the varying concentrations of ethanol. For each fuel composition tested, the observed HSI temperature was significantly higher than its corresponding ASTM-AIT temperature.

This work is important in that it not only provides HSI data for varying gasoline/ethanol concentrations; it also points out limitations in using ASTM-AIT data for predicting HSI fire initiation in an automotive field environment.