"Dale Scroggins" wrote in message
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"Capt. Geoffrey Thorpe" The Sea Hawk At Wow Way D0t C0m wrote in message
news:N6adnXfOAtwpgHXanZ2dnUVZ_sWdnZ2d@wideopenwest .com...
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Hmm. So the dozens of induction fires (some of which caused substantial
damage) that I've witnessed over the years are just as likely with a
diesel engine?

Probably not, since there is no fuel in the induction system.


10. Props are more efficient at lower RPMs, usually. Diesels have
torque to turn props slow in cruise, like a turboprop (1800-1900 RPM),
giving maybe another 5% efficiency gain, and a quieter cabin to boot.

Depends on how the engine was designed, not how the fuel is ignited.

Hmm again. So the burn characteristics of the fuel, the ability to inject
additional fuel after initiation of combustion, and the surplus of
available oxygen have no impact on engine torque curves?


On the contrary. The inabilty to mix the fuel with the air is the reason
that typical diesel torque curves flatten out at low speeds - a gas engine
can better use the air and generates more torque at the higher speeds. So
the TENDANCY is to select bore/stroke ratio's and displacements that favor
lower speeds in diesels. But there are lots of exceptions.

..
Wasn't the prospect of a relatively light weight diesel available to
homebuilders the point of this thread? No one knows if Subaru's diesel
will match the durability of a current-production avgas engine. However,
newer diesel injection methods have helped reduce internal engine forces,
so durable, light diesel engines are on the horizon.

What do you see as the advantages of diesel aircraft engines?


Primary advantage is fuel consumption - higher compression, lower pumping
losses (minor benifit for aircraft) and reduced heat loss due to the
stratified nature of the combustion all help to improve efficiency.
Increased fuel density also gives a boost to "miles per gallon" - but for
aircraft it's about "miles per pound".

Primary disadvantage is power to weight. Diesels are typically smoke
limited - they can't use all the air, so the power is limited - that's why
turbos are so popular on diesels. The higher combustion pressures also
require a heavier block and a heavier bottom end which, well, being heavier,
adds weight.

Secondary advantage is no ignition system. Secondary disadvantage is a
somewhat fussy fuel system (and, with a common rail system, you are just as
reliant on electricity as an electronic fuel injected gas engine). Probably
less of a problem for aircraft use when compared to small marine
applications - do a search on "fuel polishing"...

FWIW - look for the press propaganda on Ford's "Eco-Boost" - turbo charged,
direct injection, spark ignited gas - looks like they are shooting to get
closer to diesel fuel economy without the cost (diesel aftertreatment is
REAL expensive at the lower emission standards). Improving power to weight
lets them downsize the engine, down size vehicle componants, etc.

Of course, one could say that direct injection gasoline has all the
disadvantages of both gasoline and diesel engines. ;-)

--
Geoff
The Sea Hawk at Wow Way d0t Com
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