If it's not a diesel what is it?

We have:

Spark Igntion: carburated, manifold injected, or direct injected, but ignition source is always spark.
Compression Igntion: direct injection or indirect injection(prechamber). Ignition is due to injecting fuel into compressed air hot enough to ignite it. Timing is dependent on injection.
HCCI(homogenous combustion compression ignition): Carburated, manifold injected, direct injected. Ignition is due to compression of fuel/air mixture and timing is dependent on lambda, compression ratio, and a variety of other factors.
There are also mixed mode HCCI engines. that switch between HCCI and spark ignition or HCCI and direct injection compression ignition.

Model engines (glow and diesel) most definitely fall into the HCCI category.

http://en.wikipedia.org/wiki/HCCI