Experimental investigation of the stochastic early flame propagation after ignition by a low-energy electrical discharge

In the context of explosion protection, very conservative safety factors need to be considered, e.g. in the design of electrical devices. This is due to standards which are mainly based on empirical data as opposed to a detailed knowledge of the underlying physiochemical processes. In this work, the early phase of ignition of burnable gas mixtures close to their respective minimum ignition energy is investigated experimentally by means of high-speed schlieren imaging. Our data quantifies how the ignition process at such low energies becomes less repeatable which is evidenced by a high scattering of the flame propagation. It was found that, depending on the mixture, the flow field induced by the electrical discharge may exhibit a considerable effect on the ignition process. This effect is more pronounced for mixtures which are characterized by a large Lewis number, thus, leading to a more random flame propagation.