Wear of carbon brushes under commutation arcs in gasoline

For clarification of the behavior of electrical brushes in D.C. automotive fuel pump motors, the wear of carbon brushes sliding against a copper commutator under commutation arcs in both air and gasoline is investigated and compared with that of otherwise similar copper-graphite brushes. It is found that (i) in both environments the positive brushes of carbon wear more slowly than those of copper-graphite, (ii) the range of wear rates of both polarities and materials is fairly narrow in air but in gasoline it is wide and wear is much faster, except that the wear of positive carbon brushes is similar in both media.