Ignition Criteria and Flame Kernel Development Between Breakflash Electrodes in Explosive Gas Mixtures.

A general survey is given of the work connected with investigation of the criteria of ignition by electrical discharge in methane - air mixtures. A suggestion is made for a theoretical approach to the problem and on the basis of this approach past work is evaluated and future experiments planned. It is suggested that the energy distribution in time is of primary importance in the process of ignition and hence should be the subject of investigation. Details are given of the design and construction of a versatile experimental apparatus which was used to register the development of the ignition kernel until it reached the self-propagation stage and which recorded the relevant voltage diagrams in order to calculate the energy-time function of the discharge. With this equipment detailed investigation was made of the characteristics of the German breakflash used for testing sensitive circuits and, besides the kernel development, 'bubble' development and light emission were observed. The energy distribution, i.e. power consumption of the discharge as a function of the discharge voltage and indirectly of time is examined theoretically and from the experimental data the power function of the relevant photographs have been calculated. It was found that the kernel appears when the electrical power from the resistive circuit is at a maximum. On the basis of these findings the operation of the German breakflash is elucidated. It was shown that for resistive circuits by considering the surplus energy available during the development to self-propagation, energy values of the order of three tenths of a milliwatt can be calculated which are very near to the minimum energy values quoted by other authors for inductive and capacitive circuits