Ignition of fuel/air mixtures by radiatively heated particles

The current work examines the ignition of fuel/air mixtures by particles which have been heated up rapidly by intense electromagnetic radiation from an infrared laser source. Experiments have been conducted at relatively large beam sizes, where ignition times are a function of the irradiance. Particles in the form of fine powders were placed into a chamber filled with ignitable butane/air mixtures. Possible ignition is shown for a range of carbon based materials including different carbon blacks, graphite, the C₆₀ fullerene and diamond powder, as well as for non-reactive powders such as silicon carbide, iron-, copper- and silicon oxides. The irradiance was varied independently and results are shown to become independent of the size of the irradiated area if a sufficiently large area is illuminated. The particle size was found to have a significant impact on the time to ignition. Specifically, finer particles lead to shorter ignition times due to the higher surface area to volume ratio which reduces both particle and gas heating times. Ignition could be achieved across the whole flammability range of butane/air using carbon black and silicon carbide particles, although, near the rich flammability no ignition could be obtained with carbon black.