The discovery of high regression rate liquefying fuels for hybrid motors has generated a renewed interest in visualization experiments. In 2012, the Stanford Combustion Visualization Facility was developed to investigate the combustion of these fuels with gaseous oxygen. A major upgrade of this facility was recently completed. Details of the changes made to the facility are provided. Visual and schlieren images of the combustion of paraffin wax and oxygen at a range of operating pressures are presented, including the first schlieren images of the combustion of paraffin wax and oxygen at supercritical pressures. The nature of the combustion and the boundary layer thickness were seen to change dramatically with increasing chamber pressure, up to approximately the critical pressure of the fuel. Droplet entrainment from the surface of the fuel grain was observed at all pressures. At elevated pressures the combustion of the fuel grain was characterized by very strong surface blowing events comprised of numerous droplets.
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