|Quoting A342 (Reply 10):|
The problems you mention belong to the past. Modern diesels have both a good high-altitude performance and power-to-displacement ratio, thanks to turbochargers. Some state-of-the-art diesels are made from aluminium, basically eliminating the weight problem. But I admit, that technology is quite expensive. However, as the displacement is much lower compared to traditional Lycoming / Continental flat gas engines, the weight of aviation diesel engines isn't much higher, if at all. Vibrations are greatly decreased if balance shafts are used.
These are exactly my, admittedly non-expert thoughts. If automotive diesels are anything to go by, which I know it usually isn't, modern turbodiesels are both efficient and powerful for their size and weight. Then again, maybe the automotive thing isn't as removed as one might think. Thielert's aviation diesels are based on Mercedes automotive diesels.
And even if we forget the advanced state of automotive turbodiesel, Theilert's 2 liter turbodiesel wieghs 330 lb inlcuding "all accessories," while the O-320 weights roughly the same at 320 lb "total installed" wieght.
|Quoting SEPilot (Reply 3):|
But actually a bigger one is vibration; the power strokes on a diesel are much more violent than on a gasoline engine, and pose significant problems for the propeller and the airframe structure. I believe Thielert has minimized this by using a geared engine that turns much faster, but that has problems as well.
The Thielert engine produces its maximum power at 2300 rpm--I'm not sure what the gearbox is for--perhaps to increase the prop RPM? I can't imagine any diesel of any kind running at a significantly higher RPM than competing gasoline engines. As for vibration, balance shafts, as mentioned above, may add a bit of weight, but they certainly do wonders for smoothing things out.
The point of all this is that it seems to me like the fundamental disadvantages of diesel engines, at least the ones that we've all touched upon so far, are either no longer relevent because of the resources dumped into diesel technology in the past 15 years, or are easily solvable with a bit of development.
Again, perhaps there other, less obvious reasons for avoiding diesels in general aviation. For example, It's my understanding that those air-cooled flat 4 and 6 cylender gas engines are very modular; you can change out cylenders as needed. I can't think of any current air-cooled diesels, and I don't know if it's even practical to do so.
Dassault Mercure: the plane that has Boeing and Airbus shaking in their boots.