Roy Darlington had one in ME 4203, he called it the “Whatsit” engine. The one designed by a Kiwi was sold with a book as a kit, and known as “The One Piston Engine” by Ted Warbrook. They have a number of names (don’t think anyone can agree what they should be called), Thermo Acoustic, Pulse engines, Laminar Flow, Lag Engines, or as Ted Warbrook calls his , a One Piston Engine.
I built one back in 2005, where some are made with a test tube fr the hot end, mine is stainless steel. Roy made his two different ways as far as the steel wool packing is concerned, I made mine with a tube through the packing to a space at the end away from the piston, this is where the heat is applied. My motor has a bore of 5/8″ and a stroke of 3/4″, it runs well on a small gas flame, or a meths burner. Ian S C