Just as in a gas turbine, the cooling drag is minimized by allowing the

hot section to actually run hot. High temperature, high strength alloys, and

insulating ceramics are the key to an efficient aircraft diesel engine.

FWIW, Aluminum is just about the worst material to use in a diesel head:

low strength at high temperatures, high thermal conductivity, poor fatigue life, etc.

The argument that "...heat  has to be dissipated - - - some way." really boils

down to "because we let the heat get into the aluminum, we need to get it

back out before the piston melts."

From a standpoint of power/efficiency, an aluminum head on an automotive gas engine works against you as well. As I recall from the days of big lizards, aluminum Bow Tie heads for a small block chevy gave up 10 hp compared to iron Bow Tie heads. In a race car, the reduction in weight for the aluminum heads more than offset the power loss.

 

Also, you can get away with running a diesel a little hotter with or without coatings since you don't have to worry about preignition or detonation as you would on gas.

 

Rob