by Loïc et Jean-Yves
Following one of the possible ways to explore about pop-pop engines, Jean-Yves used pipes of bigger and bigger diameter…
A curtain rail made of steel became the next engine… Inner diameter 23.5mm, length 1.70m… A “big” blowtorch supplied with butane… And it worked… Frequency approx 2Hz. Thrust approx 130mN…
A video of this engine while running is available here ("Right-Clic/Save the target as").
In short, it can be seen that a pop-pop engine of inner diameter 40mm works… Look on the following graph what is its thrust compared with other similar engines. It looks like we have reached a plateau.
Don’t forget that if the diameter and the pipe wall surface per length unit are multiplied by 2 when the diameter evolves from 20 to 40, the volume of the engine is multiplied by 8. Therefore, considering a progressive increase of the diameter, the volume evolves quicker than the pipe surface (the ratio volume/surface grows). But the surface is an important parameter because it ensures the cooling of the system… Cooling that would become insufficient with the hot water/steam amount increase… And, as a matter of fact, on this 40mm engine we got a permanent working by forcing the pipe cooling (with water) ; thing that was not needed on previous engines…
May, 2008... Some news from the 40mm pop-pop...
Our engine with a pipe of 40mm was modified. We removed the large boilling chamber and we increased the curvature (on small engine this one seems useful). The results in terms of thrust were not better than before... The engine is just less beautiful... But the "science" is sometime like this !
...and the actual (??) biggest pop-pop of the world (!)
In February, 2008, Jean-Yves received some photos of an impressive engine. It was made by two engineering students from Netherlands, Eljoh Sneep and Bjorn Goldenbeld. They gave us their agreement for the publication on this website of some images. Apparently this engine, made with a 100L drum and a 60mm pipe, works... with a frequency of 0,25 Hz... i.e. one pulse every 4 seconds.
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