Wow, fascinating! From the title I was envisioning something akin to a solid rocket motor where the fuel gets consumed from the inside out and wondering what the point of that was, since at the end of the burn you'd still need to have enough fuselage left to avoid compromising structural integrity. (And at that point why not just build the fuselage like that from the start and use the extra mass for more liquid fuel?) But from the video it looks like this engine actually burns the hull back to front, meaning the fuselage actually gets shorter throughout the course of the flight until there's nothing left. That's really cool!