The previous pages in this section have introduced the concept of autoignition (hot surface ignition) in vehicle fires and provided some information about the surface temperatures available in vehicle environments under various operating conditions. The page showing the probabilistic nature of the ignition events also demonstrates the complicated nature of hot surface ignition. That complexity is also apparent in videos of hot surface ignition tests.

The high speed video (immediately below) shows a controlled stream of 0.25ml diesel fuel contacting a hot surface maintained at a temperature of 750 �C. The fuel vaporizes on the hot surface and vapors are somewhat contained by the recessed fixture; ignition is delayed until a combustible mixture is formed over an area of the plate. Combustion continues until all liquid is vaporized. Note: The video is being played back in quarter speed.

The next video shows a similarly controlled stream of bio-diesel (B100) contacting the hot surface maintained at 450 ⁰C in the same test fixture. This high speed video, shot at 500 frames per second and played at 1/8th speed, again shows the ignition delay and more clearly the spread of combustion through the vapor cloud. Once the hot surface ignites the vapor in one area, piloted ignition spreads rapidly through the rest of the vapor. It is easy to see how introduction of air flow could disrupt the ignition during the delay.

More information about the testing can be found in references 1 and 2.

The final video was taken by an infra-red video camera and also involved hot surface ignition of bio-diesel on a steel surface. In this test, a single drop is released onto the surface; the temperature distribution of the surface can be interpreted by comparing the color of the image to the legend. Again the liquid vaporizes on the surface and ignition is delayed until an appropriate mixture contacts an area of the surface of sufficient temperature. The video also shows the motion of the droplet on the flat surface as it vaporizes.

More information about the testing can be found in reference 3.

References

1. Davis, S., Chavez, D., and Kyotma, H., “Hot Surface Ignition of Flammable and Combustible Liquids,” SAE 2006-01-1014, 2006.
2. Somandepalli, V., Kelly, S., and Davis, S., “Hot Surface Ignition of Ethanol-blended Fuels and Biodiesel,” SAE 2008-01-0402, 2008.
3. Byers, K., Epling, W., Cheuk, F., Kheireldin, M., and Weckman, B., “Evaluation of Automobile Fluid Ignition on Hot Surfaces,” SAE 2007-01-1394, 2007.