I seem to remember that the Germans used Diesel engines on some of their aircraft during the war. It might be worth following that thread to get some operational evaluations. Check out the Junkers Jumo 205D vertically opposed diesel which was used on the Blohm and Voss BV 138c-1, or the Jumo 211d-1 inverted vee type as used on the Heinkel He111H-3. Also some aircraft used the BMW 801D radial. Don't know if the "D" suffix means Diesel.
Try contacting the Imperial War Museum, or The Fighter Collection or Old Flying MAchine Company at Duxford.
Hope this helps,
SomeFokker