re: Fire Piston

It’s not the piston itself that generates the heat, it’s the rapid compression of air inside the bore when the piston is pushed quickly into the bore that generates the heat. The piston and bore just has to contain the air so that it can be compressed. With the optimized fuel (char cloth) in the chamber, the rapid depression of the piston into the bore generates momentary heat and the fuel ignites. You basically get a glowing ember in the char cloth, and you dump/place that into your tinder. Blow on it a bit and bob’s your uncle. 

Some simple YouTube videos on it. Much easier to watch than explain.