Thielert Reenters Aero Diesel Engine, Diamond Pursues Their Installed Base

Thielert (top picture), and Diamond (bottom picture) are now both aggressively competing for market share for aircraft diesel engines. (paid subscription required)

Both engines are based on the same Mercedes diesel engine block, so the real differences are design philosophy and corporate history.

In terms of design philosophy, Diamond's engine, the AE300, is somewhat heavier, and it is implied, more robust.

In terms of corporate history, Thielert went into bankruptcy, largely driven by the warranty costs on their engine, production ramp-up issues, and financial irregularities, and the trustee basically tried to shake down the installed base by demanding ruinously expensive service and parts.

They have since returned to a going concern status, though their warranty terms are now far less generous, and their engine division has been rebranded "Centurion".

Diamond aircraft, as Thielert's best customer, was left in a serious lurch by this, and so developed its own engine, which has now been certified by the EASA, and they are using it on their new build aircraft.

The two main draws of Aero-Diesels are better fuel economy, and the ability to run on Avjet fuel, as opposed to the increasingly expensive and hard to find, particularly in austere locations, Avgas.

I think that for Theilert to compete, it needs to get a handle on reliability, as is evidenced by the line from the article, "By year-end, the company hopes to have doubled the service life of the two vital components to 600 hr," (emphasis mine) which means that they were operating at a 300 hour life (!!) (IIRC, it's the reduction gear and clutch).

By comparison, the TBO (time between overhaul) on the 0-360 is 2000 hours.

Both diesels are pushed harder to get their power than current commercially available engines, with he competing Avgas is something like the Lycoming 0-360 (whose origins are more than 50 years old) generating 180 horsepower out of 5.91 liters (361 cubic in) at 2700 rpm, while the Theilert gets 135 hp at (it's been certified for 155 hp) out of 1.9 liters at 3700 RPM, and the AE300 gets 166 hp out of 1.9 liters at 3800 rpm .

Note also that the prop speed on the diesels is 2300 RPM, while on the direct drive Lycoming it remains 2700 rpm, so propulsive efficiency per hp should be a bit better for the diesels, and their fuel consumption is on the order of ½ that of the gasoline engine.