subaru diesel

"Capt. Geoffrey Thorpe" The Sea Hawk At Wow Way D0t C0m wrote in message
news:N6adnXfOAtwpgHXanZ2dnUVZ_sWdnZ2d@wideopenwest .com...
"Dale Scroggins" wrote in message
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1. Most diesels wear more slowly than gas engines. The fuel is a better
lubricant than gasoline is, and the combustion products are a bit more
benign.

Except, of course, for the particulates. Particulates are hell on
bearings, and lungs, and...
NOx tends to run higher and isn't usually clasified as "benign"

The specific comparison I had in mind was a current-production piston
aircraft engine burning 100LL, compared to a current-production automotive
diesel engine. Given a choice of the lead compounds that collect within and
are emitted by the gasser, and the low levels of particulates deposited and
emitted by a current-production automotive diesel, I'd prefer the
particulates.

As to oxides of nitrogen, given that current production gas aviation engines
run with advanced ignition timing, have no EGR, and operate at elevated EGT
most of the time, I doubt a current production auto diesel would produce
more NOx, and would likely produce less. I'm open to numbers, if you have
them.

Again, my comparison was between current diesels and current gas aircraft
engines, not current automotive gas engines.


5. Automatic mixture control.

"mixture control is irrelevent" would be a more accurate statement.

For a turbodiesel, "automatic mixture control" is a more accurate statement.
Mixture control is quite relevent, and automatically managed.


7. Lower fire risks.

Not really.

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? And all the extra precautions we followed over the years when
fueling and defueling avgas (or mogas), compared to jetA, were a waste of
time?


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?



Given time, I can think of more. Please note that gas engines were
abandoned decades, nay, scores of years ago in other transportation
sectors. It will be the same in aviation if the weight difference shrinks
enough.


Well, there's the problem, isn't it. Making a light weight diesel that
will last.

Note: I'm not suggesting that diesels are a bad idea - they do have there
advantages. But, let's not over sell...

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?

DS