Experiments and theory on arc reignition by spark breakdown

Since the temperature recovery of an arc column and assembly cannot be analysed rigorously, a simple lumped-components model has been developed to provide an approximate solution. In this model, the experimental assembly has been divided into three components¿arc gas, ambient gas and electrodes¿and it has been assumed that the heat transfer between any two components is proportional to the temperature difference. Analysis of the model predicts a decay of gas temperature which is, in general, the sum of two exponential terms. By assuming that the spark-reignition voltage is inversely proportional to absolute temperature for the range 1500°K<T<Tambient, a prediction of reignition characteristics is possible. Spark-reignition characteristics of free-burning arcs are presented with arc duration (0.1¿400ms) as the main experimental parameter; the arc current (20, 40A), gap length (1, 5mm) and electrode diameter (3.2, 13mm) have also been varied. General agreement was found with the theory; in particular, the recovery curves for a short-gap arc indicated a dependence of the rate of recovery upon arc duration similar to that predicted by the theory. Measurements are also presented of the spark-reignition characteristics of arcs burning in a nozzle with forced gas flow, which demonstrate a considerable enhancement of the rate of recovery.