ABLATION BY PULSED PLASMA JETS

The ability of pulsed plasma jet igniters to evaporate liquid fuel whe n cold-starting alcohol- and diesel-fused automobile engines is invest igated using solid samples of wax (which is thermally similar to alcoh ol), polymethylmethacrylate and glass. The known properties of the pla sma jet imply a potential rate of heat transfer from the jet to an adj acent surface of the order of 10(8) W m-2. The computed flux threshold s for evaporation of wax and polymethylmethacrylate are of the order o f 10(7)-10(8) W m-2 and in fact a mass evaporation of 10(-9)-10(-8) kg per pulse is measured. The threshold for glass is in excess of 10(8) W m-2 and no evaporation is observed. The mass of wax evaporated is in good agreement with calculations made on the basis of a self-limiting mechanism in which an insulating layer of vapour is established at th e surface through an equilibrium between evaporation of material into the layer and convection of plasma into the layer.