Hot Surface Ignition of Ethanol-blended Fuels and Biodiesel

While ignition of flammable and combustible liquids by hot surfaces is a well-known hazard in the automotive and aviation industries, there are limited studies on the ignition characteristics of the increasingly popular automotive biofuels, such as ethanol blended fuels and biodiesel. In this paper, we present the results from over 600 ignition tests using a reproducible testing apparatus which includes: a temperature controlled hot plate, a controlled volume of liquid injected onto the hot surface and a quiescent environment. Tests were conducted to study the ignition characteristics of these biofuels and compare the results to commonly used gasoline and diesel. Hot surface tests were conducted using 100% ethanol, E85 (85% ethanol and 15% gasoline), gasoline, diesel, E-diesel, biodiesel B100, and B20 (20% B100 and 80% diesel). Based on the results of the tests, the propensity for the various fuels to ignite on a hot surface was addressed. The experimental hot surface was not designed to represent any specific automobile component nor does it necessarily represent the conditions that exist in the engine compartment after an impact. The results of this testing reaffirm that hot surface ignition has a statistical character that cannot be defined by a single ignition temperature. It was found that the minimum ignition temperature measured on a hot surface for ethanol, gasoline and diesel were at least 300°C higher than their published autoignition temperature (AIT). Ignition characteristics on a hot surface for E-85 were similar to those of 100% ethanol. Similarly, hot surface ignition temperatures for E-diesel were comparable to those of diesel. In contrast, hot surface ignition temperatures for B100 and B20 were lower than those of diesel. Further investigation into the ignition mechanisms of biodiesels will provide insight into their lower hot surface ignition temperatures and their impact on the use biodiesels in the future.