https://de.wikipedia.org/wiki/Gegenkolbenmotorg
German for opposed piston engine. I read German, but you can use a translator as the English Wikipedia version
https://en.wikipedia.org/wiki/Opposed-piston_engine does not contain as much information.
And if you really want to get serious, here is the Russian Wiki on the TE10's
https://ru.wikipedia.org/wiki/%D0%A2%D0%AD10