Interestingly enough, Commer used supercharged 2 stroke diesels in some of their buses a good few years ago. They had contra-opposed pistons with a central combustion chamber. The main advantage of the time was that there was no cylinder head or gasket to blow!
2 stroke diesels have a lot of other advantages (good power, good economy and low emissions) and i'll wager a few quid that they are about to re-emerge as car engines before too long. They just need a bit more development.