Here are some interesting related pop pop links.
Perhaps the best, most encompassing web site is the Pop Pop Pages by Vance Bass.
Here is a nanotechnology device smaller than an ant that uses propulsion system similar to a pop pop engine, but it uses audio waves instead of a flame as the power source. Here is an amazing video clip of the Acoustic Scallop in motion.
Here is a fascinating site all about steamboats big and small.
Here is a link to a Google translated page a gentleman from Argentina doing interesting research into pop pop engines
Here is the Ponyo movie trailer.