subaru diesel

"Morgans" wrote in message
...

"Dale Scroggins" wrote

The SmartCar aluminum diesel engine and the Toyota Yaris engine (Europe,
aluminum diesel) might be good candidates for small aircraft. However,
this Subaru seems to be an ideal candidate since its power and weight
specs fit so many available airframes. PRSUs are also available. I
suspect we will see these engines installed fairly quickly in European
experimentals.

No need for a PSRU. The torque band makes it perfect for direct drive.
--
Jim in NC

It's going to need a starter; diesels are hard to hand prop. And the engine
is not likely designed to handle thrust and gyroscopic loads. So, because
of starter placement and need for a well-supported prop shaft, a nose-piece
casting with bearings and a prop shaft will be needed. Incorporating
reduction gearing (or belt) and a device to smooth power pulses wouldn't add
much additional weight.

The torque curve isn't flat to maximum power. If a fixed-pitch prop is
installed that is efficient at low RPM, the engine may not be able to make
take-off RPM without a bit of mechanical advantage - or variable pitch,
which leads back to the PSRU. Since Subaru is hinting that a 200 hp version
is on its way (giving even better hp/weight ratio), a variable pitch prop
should be considered.

DS

"Dale Scroggins" wrote

It's going to need a starter; diesels are hard to hand prop. And the
engine is not likely designed to handle thrust and gyroscopic loads.

Many auto engine cranks have done well with these loads, and no extra help.

So, because of starter placement

Alternate starter schemes may be developed, and might save weight.

and need for a well-supported prop shaft, a nose-piece casting with
bearings and a prop shaft will be needed.

Not a given, IMHO.

Incorporating reduction gearing (or belt) and a device to smooth power
pulses

Smoothing power pulses results in heating up the device, which means it is
robbing power and efficiency. Double or triple bad thing. Weight, power,
and reliability.

wouldn't add much additional weight.

I've heard that so many times, and it all adds up to an overweight airplane.

The torque curve isn't flat to maximum power.

True, but how much extra power will have to be made, to haul around the
extra weight?

If a fixed-pitch prop is installed that is efficient at low RPM, the engine
may not be able to make take-off RPM without a bit of mechanical
advantage - or variable pitch, which leads back to the PSRU.

PSRU's are HEAVY! Why add one, if it is not absolutely needed? Extra
weight has to be well justified, as does the possibility of extra components
causing possible extra failures. It is hard to imagine that hauling around
the extra weight could be justified, with a torque curve like that engine.
It would need to make a lot of extra HP to justify a PSRU, to me.

Since Subaru is hinting that a 200 hp version is on its way (giving even
better hp/weight ratio), a variable pitch prop
should be considered.

Why?

With conventional aircraft engines, they make best power and torque at up
around 2700 RPM. If you have to run too big of a prop to utilize 200 HP,
then you need constant speed to keep from breaking supersonic.

If you have an engine running best power (or close to it) and best torque at
23 or 24 hundred RPM, you can run a bigger prop, and keep the tips slow
enough, without the extra weight and complexity of constant speed props.

Don't get me wrong. I'm not against PSRU's in all cases. I am against
extra weight and complexity when it is not absolutely necessary. I don't
think a clear case has been made, for this engine.

Wait until it is being used, and see how well it does, is my opinion. It
will let us know, by how it does after it has been eXperimented with, I
believe. You may be surprised. I might be, too. Until then, keep an open
mind.
--
Jim in NC

wrote in message ...
On Mar 22, 9:33 pm, "Dale Scroggins"
wrote:
"Blueskies" wrote in message

...



"Morgans" wrote in message
...

"Philippe Vessaire" wrote in message
news:19459447.yEvPs9oxTh@GastonCoute...
Hello

Torque curve page 6

http://www.subaru.fr/special/pdf/doc...esel_lo_08.pdf

Holy crap! That thing has the peak torque, and it is almost a level
line, from about 1600 rpm to about 2400 rpm!

That sucker should really pull a big prop, and well!
--
Jim in NC

Is the price of diesel fuel 25% above gasoline prices everywhere?
Jet A costs the same as 100LL now also, so what is the benefit?

SNIP
2. No ignition system needed.

Not to be a ball-buster, but the injection systems for the new
generation of diesels is incredibly fancy. From a risk analysis
standpoint, it is hard to say whether this system in place of magnetos
is a gain or a loss.

3. Turbocharging a diesel is a win-win proposition. EGT is lower, so turbo
system parts last as long as the engine, usually. Turbocharging improves
both performance and fuel efficiency (not always true for gassers).

True, but boost levels in diesels inversely effect their reputation
for reliability.

SNIP

8. I can make biodiesel for 67 cents a gallon. You or I can buy off-road
diesel or heating oil for much less than either auto gas, avgas or jet A.

Biodiesel gels at a higher temp than does winter diesel, and be damned
sure you have no rubber in the fuel system. And the 67 cents is
quoted for recycled oil. Not my first pick at altitude.

9. For a given trip, less fuel is needed, both in volume and weight. 25%
to 35%, depending on the trip profile. If the diesel is turbocharged and
gasser is not, the diesel's ability to cruise significantly higher may
result in a bigger efficiency spread.

This is dependent on tuning the boost map, and whether the blower is
big enough. Off the shelf this may or may not be true. I have not read
flight tests for any new European diesels which have been impressive
in high altitude performance. I doubt this is because of any
fundemental flaws, but rather performance tuning.

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.

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.

DS

I dig your enthusiasm. Please post if you hear of any new diesel/
biodiesel aviation projects. I would be interested in reading any
related results. I believe that the new generation of diesels are the
long term solution for keeping GA operating costs down. But it will
take a while.

-Matt


Why any sort of reciprocating engine?...small turboprops would be the best solution of they can get the mass fuel flow
problems resolved...

"Blueskies" wrote in message
t...
...

Why any sort of reciprocating engine?...small turboprops would be the best
solution of they can get the mass fuel flow problems resolved...


Nothing like the laws of thermodynamics and material limitations to ruin a
good party.

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

"Capt. Geoffrey Thorpe" The Sea Hawk At Wow Way D0t C0m wrote

Nothing like the laws of thermodynamics and material limitations to ruin a
good party.

Yep. Small turbine engines are not fuel efficient, and yet they are
expensive. The materials are exotic, and so are the methods that have to be
used to construct the engine.

The gains that have been made with small turbines are amazing enough to me,
but they still have not gone to where they need to be, to be practical.

That said, I still want one of those rigid skydiving wings, with the 4 pack
of model jet engines! What a rush that HAS to be!
--
Jim in NC

Morgans wrote:

"Capt. Geoffrey Thorpe" The Sea Hawk At Wow Way D0t C0m wrote


Nothing like the laws of thermodynamics and material limitations to ruin a
good party.


Yep. Small turbine engines are not fuel efficient, and yet they are
expensive. The materials are exotic, and so are the methods that have to be
used to construct the engine.

The gains that have been made with small turbines are amazing enough to me,
but they still have not gone to where they need to be, to be practical.

That said, I still want one of those rigid skydiving wings, with the 4 pack
of model jet engines! What a rush that HAS to be!


If you got the money, I got the time!



--
(remove the X to email)

It's never too late to be the person you might have been.
George Elliot

"Dale Scroggins" wrote in message
...

...
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"

5. Automatic mixture control.

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

7. Lower fire risks.

Not really.

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.


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...

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

"Capt. Geoffrey Thorpe" The Sea Hawk At Wow Way D0t C0m wrote in message
news:N6adnXfOAtwpgHXanZ2dnUVZ_sWdnZ2d@wideopenwest .com...
"Dale Scroggins" wrote in message
...

...
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

"Dale Scroggins" wrote in message
...

"Capt. Geoffrey Thorpe" The Sea Hawk At Wow Way D0t C0m wrote in message
news:N6adnXfOAtwpgHXanZ2dnUVZ_sWdnZ2d@wideopenwest .com...
...
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
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

"Capt. Geoffrey Thorpe" The Sea Hawk At Wow Way D0t C0m wrote in message
...
"Dale Scroggins" wrote in message
...

"Capt. Geoffrey Thorpe" The Sea Hawk At Wow Way D0t C0m wrote in
message news:N6adnXfOAtwpgHXanZ2dnUVZ_sWdnZ2d@wideopenwest .com...
...
...
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".

Oh, I forgot, they can run on Jet fuel if the injector pump will tolerate
it...



On the downside, diesel fuel is good for growing algae, dunno about jet
fuel - but given the number of hanger queens at the typical airport, I
assume we will find out when diesels make a dent in the aircraft market.







--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.