The US designed direct drive Delta Hawk Turbo/Super Charged V4 two stroke of 160 to 200hp is the best bet at the moment. The company has a positive cash flow, selling them as drone engines.
A 160hp one is being tacked on the front of a 172 and they plan to put two 200hp ones into a Cessna 337. Aiming at the Lycoming IO360 market.
This engine is well on the way to certification.
http://www.deltahawkengines.com/
There are about 10 Aero Diesels in development at the moment with two certified, the French SMA a bit of a boat anchor and the the Thielert over complicated.
There are two opposed piston type engines, one flying by Diesel Air 2 cyl 4 piston and Jade Air are developing a 3 cyl 6 piston version, both with twin crank shafts.
Then there is Diesel Aero, Vulcan Aircraft Engines, Eco Motors and of course.
The 8 cyl Zorche, I think this is the best design of the lot, but a joke of a development programme, I think they are a scam just to get EU research funds.
Then there was Continetal flat 4, 2 stroke with a 90 degree offset crank
and pistons shuttling from side to side, one bang every quarter of a rev.
The sleeper is a radicaly new design of 4 stroke engine called the Rand Cam,
two main moving parts, a rotor and 12 sliding vanes, the two cams are set at 90 degree facing each other, giving a constant spacing. The vanes slide back and forward between them when the rotor is rotated. A 6 inch by 6 inch test model gives 42 hp. Will make wonderfully light compact engine with 24 power pulses per rev.
http://www.regtech.com/
So there are tons of Aero Diesels in development, I just don't think the Thierlert will be the winner in the long run, to complicated and a direct drive 2 stroke is smoother and has less harmonics then the 4 strokes.
Note Diamond are developing there own 180 hp diesel, I think they are fedup with the Thierlert problems.