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2-stroke diesel is the (near) future?



 
 
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  #61  
Old May 15th 05, 03:23 PM
wingsnaprop
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Actually, it is Otto, as in 4-stroke spark ignition.

Dude, MJC was Joking

  #62  
Old May 15th 05, 03:33 PM
wingsnaprop
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Yea me two! 90% spelling accuracy on Usenet is what should be
acepted without comment! My opinion.

  #63  
Old May 15th 05, 04:12 PM
Don Stauffer
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Sport Pilot wrote:


A compression ignition engine is not always a Diesel engine. Not sure
if Mr. Diesel invented comprssion ignition, but they used to be common
for model aircraft. Though called Diesel's modelers are often reminded
they are not really Diesel's.


Good point. I think Rudy did indeed invent compression ignition. And
the old Ford Proco engine designs were virtually Diesel cycle engines
even though they had spark ignition. In fact, that idea seemed like a
really good one to me, and I would like to know why it never went
anywhere. Was the injection system just to complicated for production?
  #64  
Old May 15th 05, 07:41 PM
Sport Pilot
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Smitty wrote:
In article .com,
"Sport Pilot" wrote:

HELLO! It's just the friggin usenet! Most of us don't even know

who
we are talking too. Some of us have more important things to do,

such
as correspondance on a 10 million dollor project. You bet that

baby
gets proofread, spell checked, grammer checked, proofread, maybe

ask a
co worker to proofread it, see what I missed, etc.


Hello? You mean "to," (a preposition and therefore a word with which

you
ought not end a sentence, anyway) "correspondence," "dollar," and
"grammar?" I'm not picking on you, particularly, but the pervasive
ignorance of spelling, grammar, punctuation, homonyms, sentence
construction, ad infinitum, makes me ****ing sick. And it isn't just
usenet, it's everywhere, even in your ten million dollar report,

because
your computer can't fix everything and your coworkers are as

apathetic
as you are. We're becoming a nation of ignorant idiots. I think

that's a
bad thing, and a dangerous one. If we knew as little about airplanes

as
we did the English language, and flew them as carelessly as we write,


we'd all be dead by now.



Ass I said I really don't care. In fact your anger only make sme want
to make mroe miostakes. So i have not coreected any typos at all in
this one.

  #65  
Old May 15th 05, 08:00 PM
Sport Pilot
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There's no fundamental limit thats any different than
a gasoline engine, really, but up until now there's not been a demand
for high-RPM diesels.


Thought I had responded to this before, but cannot find it.

There IS a fundamental reason diesels do not turn as many revolutions
as a gas engine. Injecting the fuel throught most of the expansion
cycle prevents speed, but does give a constant push. You could shorten
the injection so that the end of the injection is closer to TDC, but
then it would be more of an otto cycle. If you put too much fuel at or
near TDC then you would have the same problem as an otto engine with
high compression and low octane fuel. Diesel fuel is not high octane.

  #66  
Old May 15th 05, 09:11 PM
Thomas Tornblom
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Luke Scharf writes:

Steve wrote:
But there are more and more small diesels that run just as fast as
gasoline engines. There's no fundamental limit thats any different
than a gasoline engine, really, but up until now there's not been a
demand for high-RPM diesels.



When I was reading about the Volkswagen TDI engine, I vaguely remember
coming across someone who said that the redline of that engine was set
by the speed which which the burning fuel expanded.


My '01 180 bhp Audi 2.5 tdi V6 has a redline of 4500 rpm.



Sounds rather fundamental to me - but, then again, I'm a computer guy.

-Luke


Thomas
  #67  
Old May 15th 05, 09:17 PM
Thomas Tornblom
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Don Stauffer writes:

Sport Pilot wrote:
You can only get so much speed when you inject the fuel through the


combustion or expansion cycle. High speed diesels get more speed by
injecting more of the fuel early. But an aircraft engine doesn't need
to turn more than 2500 RPM so we should be able to get the benifit of
the longer burn time.



True, but even 2500 rpm is a high speed Diesel. When we speak of low
speed Diesels, those are like the big ship and stationary engines that
run maybe 800 rpm max.


I once had the opportunity to visit the engine room of one of the big
ferries cruising between Sweden and Finland. It had four engines and
two props.

The idle speed was 100 rpm and full speed was 150 rpm.

I could not hear any difference between 100 and 150 rpms. But then I
never knew what noise came from the propulsion engines. There were a
lot of other helper engines making a lot of noise.

The props were geared 2:1, so they did 75 rpms at full speed.

Thomas
  #68  
Old May 16th 05, 04:44 AM
Luke Scharf
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Thomas Tornblom wrote:
Luke Scharf writes:


Steve wrote:

But there are more and more small diesels that run just as fast as
gasoline engines. There's no fundamental limit thats any different
than a gasoline engine, really, but up until now there's not been a
demand for high-RPM diesels.



When I was reading about the Volkswagen TDI engine, I vaguely remember
coming across someone who said that the redline of that engine was set
by the speed which which the burning fuel expanded.



My '01 180 bhp Audi 2.5 tdi V6 has a redline of 4500 rpm.


That's about where the one on the Jetta was -- right around 4500 rpm.
The displacement on the Jetta is only 1.6 liters, though... I wonder
what dimensions are similar to make the smaller engine redline at the
same speed?

When I got to the redline, the engine seemed to politely refuse to go
any faster. Not like the screaming tantrum I'm used to from my
run-of-the-mill gas engines as I open the throttle.

I dig diesels. :-)

-Luke
  #69  
Old May 16th 05, 05:35 PM
Steve
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Morgans wrote:

"Steve" wrote


As already stated, 2-stroke diesels really don't have a power-to-weight
advantage over 4-strokes. They still have to have a camshaft and
exhaust valves (they aren't like weed whacker engines, you know), so
they don't save that weight. Plus they have to have a blower for
scavenge air. The only area where they save weight is in that the
connecting rod and crank can be lighter, and that only helps offset the
added weight of the blower.



How about the fact that they have power pulses in each revolution? They
could possibly have half the displacement, and still get the same power, (or
close to it) with less weight than the double displacement 4 cycle. Yes,
the blower weight is added, but it is nice to make good power, way up there.



The blower also takes away a significant chunk of crankshaft power. The
blower has to do the same net work as those "non power" strokes in a
4-cycle diesel because its doing the same job- expelling burnt mixture
and bringing in fresh air. You can't get something for nothing.

This is all old-hat. 2-stroke diesels have been in widespread use since
Winton developed the basic foundation for what became both the EMD and
Detroit Diesel 2-stroke engine architecture back in the 1920s. 2-strokes
became very simple to service and reliable, but they rarely won on
either fuel efficiency or total power output per unit weight. That's why
you find 2-strokes in locomotives and ships where weight doesn't matter
(or is a benefit), but they all but disappeared from on-road
applications by the end of the 1970s and DID completely disappear by the
turn of the century.
  #70  
Old May 16th 05, 05:39 PM
Steve
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Luke Scharf wrote:

Steve wrote:

But there are more and more small diesels that run just as fast as
gasoline engines. There's no fundamental limit thats any different
than a gasoline engine, really, but up until now there's not been a
demand for high-RPM diesels.



When I was reading about the Volkswagen TDI engine, I vaguely remember
coming across someone who said that the redline of that engine was set
by the speed which which the burning fuel expanded.

Sounds rather fundamental to me - but, then again, I'm a computer guy.

-Luke


In almost ALL real-world engines, the actual limit is set by the point
at which some mechanical component would fail. The engine's torque *may*
drop off well before the mechanical failure point if it can't ingest
enough fuel or air at high speed. In the case of a diesel, you can
pretty much increase the burn rate to as high as the mechanical parts
can tolerate by increasing turbocharger boost (and injection rate to
match). Since detonation isn't possible (no fuel exists in the cylinder
until combustion is supposed to begin anyway) the only limits to boost
pressure are mechanical in nature. In practical terms, no one really
wants or needs a 9000 RPM diesel, though.
 




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