Small hot surfaces can ignite explosive atmospheres in dependence on their temperature and their dimensions. Heating of small particles leading to ignition can be originated by several potential ignition sources like optical radiation, ultrasound or mechanical friction and grinding. The objective of this work is to investigate the ignition capability of single inert particles in dependence on their temperature and dimensions. This is done by a combination of measurements and numerical simulations to ensure valid limit values for the particle temperature. Artificially produced particles of 0.5 mm to 1.3 mm diameter are placed in different explosive atmospheres of hydrogen or different hydrocarbons in air. The inert particles are heated continuously by IR laser light with a specific power. The time-resolved temperature of the particle is measured by two-wavelength pyrometry. The temperatures at which ignition occurs are evaluated with respect to the particle diameter and the mixture composition. The experimental results are compared with numerical simulations using detailed reaction mechanisms. Solving the well-known mass, species and energy equations for spherically symmetrical one-dimensional flames using a time-integration method, ignition temperatures have been determined for selected diameters and mixture compositions.
ignition source, hot surface, mechanical spark