Not too sure about diesels in aviation. . .Yes they are more fuel efficient, mostly because diesel fuel contains more BTU's than petrol, but there again it weighs more. Vibration is another issue, as is cold starting, the need for larger batterys and a heavy duty starter, (compression ratio's are over 17:1, the smaller the engine, the higher they are). Diesels engines weigh more than a similar power output petrol engine, and generally need to be of greater capacity to produce the same power output, and last but not least, there is always the fuel gelling problem in cold temps. . .Over-the-hiway diesels use their cooling systems to warm the fuel in the tanks before pumping it to the engine. Using diesel fuel that does not gell in cold temps defeats the BTU advantage, as only the lighter fuel elements can be used (the heavier elements of course contain more BTU's), and the chemical additives to aid cold temp flow problems increase the cost of the fuel significantly.. .In short Diesels in aviation would be wonderful for fair weather flying, (if the vibration issue and the serious exhaust emission problems can be solved), but high altitude, cold weather flying contains serious disadvantages for diesel engines. (They also run a lot cooler, cabin heat?). .White Bear.