RC engines were my first thought when I saw this, but I think they're more like a hot bulb two-stroke than a true diesel. Nevertheless it's a way to think about the problem.
A conventional gas engine won't hold up to the continued pounding of a diesel, but this thing only has to hold up long enough to survive the competition. Scooter engines aren't terribly expensive, get three: one for testing and prototyping, two for the competition (one primary and one backup).
This guy talks specifically about modifying existing four-stroke RC engines into diesels, he could add some fuel to your fire.
Unless I misrecall the most competitive teams are now insulating their engines to keep the heat in, and do low speed pulse-and-glide to maximize matching their engine's loading to its best BSFC point.