I am beginning to understand that the Papp engine was a cavitation based device.
In the 1960's Papp used water for his fuel. Papp must have produced water crystals in the compression part of the cylinder cycle where the volume of the cylinder was decreasing. During this increasing pressure environment inside the cylinder, cavitation bubbles must have formed thereby producing ultra dense water crystals. For example, some larger diesel engines suffer from cavitation due to high compression and undersized cylinder walls. Vibrations of the cylinder wall induce alternating low and high pressure in the coolant against the cylinder wall. The result is pitting of the cylinder wall, which will eventually let cooling fluid leak into the cylinder and combustion gases to leak into the coolant. To stop the cavitation based erosion of the cylinder walls and the subsequent loss of compression over time, Papp went to noble gases which produce ultra dense noble gas crystals during the compression stage of the cylinder cycle but the formation of ultra dense noble gas crystals did not damage the cylinder walls. When Papp fired a spark, the ultra dense noble gas crystals exploded as happens in the Holmlid experiment when the ultra dense hydrogen cycltals produce atomic particle fragments that move outward at 3/4 the speed of light. Currently, Holmlid does not capture that huge amount of energy inherent to his expanding plasma. To utilize the energy in the expanding plasma, Holmlid might capture that nuclear powered expanding plasma as Papp once did in an engine design using ultra dense hydrogen as fuel.
