Modeling a new spray process combining plasma and HVOF

This study deals with the numerical simulations and experimental observation of a new industrial thermal spray process developed at Inasmet Tecnalia. The process, called "oxi-fuel ionization" (OFI) is a supersonic combustion process enhanced by the combination with a plasma source. The arising combustion process is characterized by its stability within a broad range of fuel/oxidant conditions and the ability to produce high quality coatings using gases with rather low gross heating values and lower gas consumption than most of the conventional HVOF guns. The mathematical model involved the formation of the plasma jet, combustion process and supersonic flow issuing from the spray torch. It made it possible to investigate the effect of the plasma on the gun operation and more specifically on the velocity and temperature fields of the gas flow inside and outside the gun. The model equations were solved using the CFD Fluent 6.3 code and predictions were compared with experimental observations. The benefits of the plasma jet will be discussed in the light of predictions and fuel combustion mechanisms.