In uk.rec.motorcycles The Older Gentleman wrote:
Stuart Fields wrote:

Of course there are a bunch of Subaru powered aircraft out there with and
without PSRUs. All that said, it is still hard to beat the Lycoming in
every thing but acquisition costs.

As one who's just bought the car that houses it, it will be interesting
to see whether the Subary flat-four diesel finds any aircraft
applications.

Are there any diesel aer-engines, or diesel car engines frequently used
in aircraft? I had the impression that diesel aero-engines died with
airships and the Junkers 86, but I'm always willing to learn....

Yup, Thielert engines are used by Diamond aircraft.
http://www.centurion-engines.com/
Diesel engines running on aviation kerosene.

--
03 GS500
66 Velocette LE Mk3
68 Bantam D14S
81 CB250RS