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2-stroke diesel is the (near) future?



 
 
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  #121  
Old July 12th 05, 02:45 PM
Don Stauffer
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Sport Pilot wrote:
>
> Don Stauffer wrote:
>
>>Sport Pilot wrote:
>>
>>>Completely wrong, the Otto cycle has nothing to do with four stroke
>>>engines. Don is right its not four cycle, I used it incorrectly. The
>>>Otto and Diesel cycles are actually refering to the thermodynamics
>>>chart of temperature pressure and volume, they invented their cycles on
>>>paper and books, the engines we use are only close approximations. The
>>>two stroke ignition engine uses the Otto cycle as it is has the four
>>>phases of intake, compression, power, and exhaust, and the pressure is
>>>not constant. The Diesel two stroke is a Diesel cycle because it also
>>>includes the same phases and the fuel burns at a fairly constant
>>>pressure.
>>>

>>
>>I guess I'd quibble with the statement that the Otto cycle has nothing
>>to do with four-stroke engines- it was the first successful cycle to
>>incorporate four strokes. yes, there are other four stroke cycles, but
>>the Otto cycle is still by far the most common. There have been several
>>other four-strokes, several two-strokes, at least on six stroke- I
>>suspect several also.
>>
>>New IC engine designs are among the most numerous US patents. Just
>>because something is patentable, of course, does not make it good or
>>successful, and most of these patents were for approaches that offered
>>insufficient advantages.
>>
>>BTW, as I understand the new Miller cycle, I don't consider it a truly
>>new cycle- just a clever mod on the Otto. I don't consider the Otto
>>cycle to require valve openings at closings at the top or bottom dead
>>center, exactly.

>
>
> The confusion is that Otto invented the first four stroke engine and
> called it the Otto cycle, not because of thermodynamics but because he
> put it in a motorcycle. However the thermodynamic cycle can be
> reproduced with a two stroke engine. Its just that the intake and
> exhaust cycle's are much shorter.
>


I am not sure what you mean by exhaust and intake "cycles". There is
one cycle- the actions that the engine goes through before everything
repeats. Do you mean the portions of the cycle during which the exhaust
and intake take place- they definitely take less crankcase revolution angle.

In the Otto cycle it is easy to break it down into four operations, each
lasting one stroke. A two-stroke is more complicated, because it still
has (existing, contemporary ones, do anyway) four seperate functions of
intake, compression, combustion and exhaust, but have to do it in two
strokes.
Ads
  #122  
Old July 12th 05, 02:54 PM
Sport Pilot
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Don Stauffer wrote:
> Sport Pilot wrote:
> >
> > Don Stauffer wrote:
> >
> >>Sport Pilot wrote:
> >>
> >>>Completely wrong, the Otto cycle has nothing to do with four stroke
> >>>engines. Don is right its not four cycle, I used it incorrectly. The
> >>>Otto and Diesel cycles are actually refering to the thermodynamics
> >>>chart of temperature pressure and volume, they invented their cycles on
> >>>paper and books, the engines we use are only close approximations. The
> >>>two stroke ignition engine uses the Otto cycle as it is has the four
> >>>phases of intake, compression, power, and exhaust, and the pressure is
> >>>not constant. The Diesel two stroke is a Diesel cycle because it also
> >>>includes the same phases and the fuel burns at a fairly constant
> >>>pressure.
> >>>
> >>
> >>I guess I'd quibble with the statement that the Otto cycle has nothing
> >>to do with four-stroke engines- it was the first successful cycle to
> >>incorporate four strokes. yes, there are other four stroke cycles, but
> >>the Otto cycle is still by far the most common. There have been several
> >>other four-strokes, several two-strokes, at least on six stroke- I
> >>suspect several also.
> >>
> >>New IC engine designs are among the most numerous US patents. Just
> >>because something is patentable, of course, does not make it good or
> >>successful, and most of these patents were for approaches that offered
> >>insufficient advantages.
> >>
> >>BTW, as I understand the new Miller cycle, I don't consider it a truly
> >>new cycle- just a clever mod on the Otto. I don't consider the Otto
> >>cycle to require valve openings at closings at the top or bottom dead
> >>center, exactly.

> >
> >
> > The confusion is that Otto invented the first four stroke engine and
> > called it the Otto cycle, not because of thermodynamics but because he
> > put it in a motorcycle. However the thermodynamic cycle can be
> > reproduced with a two stroke engine. Its just that the intake and
> > exhaust cycle's are much shorter.
> >

>
> I am not sure what you mean by exhaust and intake "cycles". There is
> one cycle- the actions that the engine goes through before everything
> repeats. Do you mean the portions of the cycle during which the exhaust
> and intake take place- they definitely take less crankcase revolution angle.
>
> In the Otto cycle it is easy to break it down into four operations, each
> lasting one stroke. A two-stroke is more complicated, because it still
> has (existing, contemporary ones, do anyway) four seperate functions of
> intake, compression, combustion and exhaust, but have to do it in two
> strokes.


Sorry for the confusion, the two stroke doesn't take a stroke for those
functions so I used cycle, can't think of anything else to call it.

  #123  
Old July 12th 05, 09:55 PM
Morgans
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"Don Stauffer" > wrote

> A two-stroke is more complicated, because it still
> has (existing, contemporary ones, do anyway) four seperate functions of
> intake, compression, combustion and exhaust, but have to do it in two
> strokes.


And some of the operations are happening simultaneously.
  #124  
Old July 12th 05, 10:30 PM
Bill Daniels
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"Morgans" > wrote in message
news
>
> "Don Stauffer" > wrote
>
> > A two-stroke is more complicated, because it still
> > has (existing, contemporary ones, do anyway) four seperate functions of
> > intake, compression, combustion and exhaust, but have to do it in two
> > strokes.

>
> And some of the operations are happening simultaneously.


There is one very efficient 2-stroke variant that does have separate and
distinct intake, compression, combustion and exhaust functions - the
opposed-piston 2-stroke diesel with the pistons driven by cams, not
crankshafts.

As the pistons move apart (power), the exhaust port is uncovered first by
one piston (exhaust) and then the intake is opened by the other piston so
high pressure air from the supercharger can scavenge the last bits of
exhaust gas from the space between the pistons. After the cylinder is
scavenged, the first piston closes the exhaust port leaving the intake port
open so the supercharger can charge the cylinder with air (intake). Then
both pistons move together closing the intake port (compression). Fuel is
injected directly into the space between the pistons which forms a spherical
combustion chamber (ignition). The cams are designed to optimize the timing
and duration of the port openings as well as contour the compression and
power strokes.

This design makes extreme demands on metallurgy and lubricants so is just
now becoming practical.

Bill Daniels

  #125  
Old July 13th 05, 02:19 PM
Sport Pilot
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Thinking a very large version of that was used before?

  #126  
Old July 17th 05, 05:48 PM
Don Stauffer
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mastic wrote:
> "Sport Pilot" > wrote:
>
>
>>Here is an animated link showing the differances of the Otto and Diesel
>>cycles.
>>
>>http://www.ulb.ac.be/sma/testcenter/...osedcycle.html
>>
>>Notice the near instant burning in the example gives very nearly a
>>constant volume, in actual practice some compression is going on at
>>this time.
>>
>>Also during a Diesel cycle it is hard to maintain a constant pressure,
>>it would actually drop off, especially near the end of the down stroke.

>
>
> But both are still otto cycles.
> If you think the fuel burns instantly in a spark engine remove the
> exhaust manifold and run the engine, observe the flame exiting the
> exhaust port.


Indeed, if it does burn "instantly", that is detonation. However, it
burns more rapidly in a SI engine than in a true Diesel cycle Diesel. In
fact, it is astonishing to me how fast one can turn even relatively
large SI engines, such as Formula 1 car engines. Is there no limit :-)
  #127  
Old July 17th 05, 05:50 PM
Don Stauffer
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mastic wrote:
>
> Otto cycle = four stroke, nothing to do with fuel injection, burn
> rates, phases of the moon or the flavor of ice cream.
> See
> http://en.wikipedia.org/wiki/Otto_cycle


I thought the Otto cycle was supposed to have the power stroke be
ideally completely adiabatic.
  #128  
Old July 17th 05, 06:05 PM
JazzMan
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mastic wrote:
>
> >> And some of the operations are happening simultaneously.

> >
> >There is one very efficient 2-stroke variant that does have separate and
> >distinct intake, compression, combustion and exhaust functions - the
> >opposed-piston 2-stroke diesel with the pistons driven by cams, not
> >crankshafts.
> >
> >As the pistons move apart (power), the exhaust port is uncovered first by
> >one piston (exhaust) and then the intake is opened by the other piston so
> >high pressure air from the supercharger can scavenge the last bits of
> >exhaust gas from the space between the pistons. After the cylinder is
> >scavenged, the first piston closes the exhaust port leaving the intake port
> >open so the supercharger can charge the cylinder with air (intake). Then
> >both pistons move together closing the intake port (compression). Fuel is
> >injected directly into the space between the pistons which forms a spherical
> >combustion chamber (ignition). The cams are designed to optimize the timing
> >and duration of the port openings as well as contour the compression and
> >power strokes.
> >
> >This design makes extreme demands on metallurgy and lubricants so is just
> >now becoming practical.
> >
> >Bill Daniels

>
> The British Deltic diesel engine use opposed pistons with normal
> crankshafts, three banks of cylinders, three crankshafts in a
> triangular lay out. A very compact light weight engine. Large HP
> engines something like 1500 - 3000 HP, used in boats and railway
> locomotives.


That was a good way to stuff 2,500 high-hour horsepower into a volume
only 6' wide, 9' long and 7' tall back then. Not as efficient as modern
designs, but way ahead of the curve back then. Note, the Deltic was a
direct-drive locomotive power system.

JazzMan
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  #129  
Old July 18th 05, 12:39 AM
~^Johnny^~
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-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On Sun, 17 Jul 2005 11:48:43 -0500, Don Stauffer
> wrote:

> it is astonishing to me how fast one can turn even relatively
>large SI engines, such as Formula 1 car engines. Is there no limit
>:-)


http://www.petting-zoo.net/~deadbeef/archive/5304.html


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--
-john
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