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2-stroke diesel is the (near) future?



 
 
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  #101  
Old May 25th 05, 07:01 PM
Steve
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Don Stauffer wrote:

SOME diesels are turboed. Many are not. Some Diesels are normally
aspirated. Some are supercharged with geared chargers. Some are
turboed. It is by far an overgeneralization to claim that all Diesels
are supercharged, even more so to say they are all turbo-supercharged.


I believe that if you look at modern diesels currently being produced
and sold, you'll find virtually NONE rated at more than 50-60 horsepower
that are not turbo-supercharged. And equally few that are strictly
mechanically blown (the Detroit Diesel 2-strokes are no longer in
production). The VAST majority are, indeed, turbo-supercharged.
  #102  
Old May 25th 05, 07:03 PM
Steve
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Sport Pilot wrote:


Steve,
As you said power is torque * RPM, so for the same torque more speed
is power.


Or for the same SPEED, more TORQUE is more power. That's the part of the
equation that you've never acknowledged.



Your example is a poor one most diesels of equivelant size will deliver
more torque at less RPM and have less total horsepower.


Not always true (obviously), and when looking at modern diesels its not
even GENRALLY true anymore. That's EXACTLY why I picked the example that
I did! If you don't like the Dodge comparison, go look at a
Ford/Navistar 6-liter diesel and compare it to the closest-sized Ford
(5.4L) gasoline engine tuned for a truck application. 10 years ago, the
diesel would have won on low RPM torque, but been lacking in peak HP.
That is no longer the case most of the time, because diesels are now
*always* turbocharged, and most of the time have modern electronic
injection control over both injection rate AND duration.

I don't know
where you found that pitiful Dodge 5.9 liter engine.


There's nothing pitiful about it at all, it was an EXCELLENT truck
engine used from 1972 until 2003. When built for power rather than
torque, it can easily put out well over 400 Hp without turning 7000 RPM,
but as delivered in factory trucks, it was tuned for a torque band
that's flat as Kansas over about a 3500 RPM span, and that results in a
rather modest 230 HP.

I have a 4.7 V8
in my Grand Cherokee and it puts out 260+ HP.


The 4.7 is the replacement for the 5.2, and while a fine engine in its
own right, its a little bit low in the torque department. It doesn't
move the fullsize Ram pickup or even the Durango with much authority-
the old lower-HP rated 5.9 actually "feels" a lot peppier in around-town
driving because it has more torque below 3000 RPM than the 4.7L does,
despite a lower peak HP rating. That's a symptom mostly of its small
size- when you excessively constrain the displacement of an engine, you
start HAVING to spin it faster and faster to get the same power and you
sacrifice torque at the lower RPM levels- Which is a key part of the
point I've been driving home. Modern gasoline-powered cars and trucks
tend to have very high peak horsepower ratings- and yet many of them
feel weak compared to older cars, simply because all that high-RPM
horsepower comes at the expense of useful low-RPM torque, and they need
5- and 6-speed transmissions just to match the performance of older
torquier engines.

Gas engines have been pushed smaller and lighter by fuel economy and
emissions considerations, resulting in peaky torque curves, poorer
low-RPM torque, and higher peak HP to compensate.
  #103  
Old May 25th 05, 07:08 PM
Thomas Tornblom
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Steve writes:

Thomas Tornblom wrote:

Steve writes:

More speed is NOT more power any more than more torque at the same
speed is more power.

uh?



huh. Read it again.


Ok.

English is not my native language, and I read the sentence such that
the "NOT" in the first half also implied that there was an implicit
"NOT" in the second half, which made the statement wrong.


More torque at the same speed *is* more power.



That's exactly what I've been saying. You can get more power by
increasing torque OR rpm or both.


Then we agree :-)

Thomas
  #104  
Old May 25th 05, 09:45 PM
Steve
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Thomas Tornblom wrote:

Steve writes:


Thomas Tornblom wrote:




Ok.

English is not my native language, and I read the sentence such that
the "NOT" in the first half also implied that there was an implicit
"NOT" in the second half, which made the statement wrong.



And I'll admit, it was a poorly written sentence. My bad.
  #105  
Old May 25th 05, 11:15 PM
Morgans
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"Steve" wrote

I believe that if you look at modern diesels currently being produced
and sold, you'll find virtually NONE rated at more than 50-60 horsepower
that are not turbo-supercharged. And equally few that are strictly
mechanically blown (the Detroit Diesel 2-strokes are no longer in
production). The VAST majority are, indeed, turbo-supercharged.


Not true of some of our school busses that were produced in the past 5 or so
years. They make up for the lack of super or turbocharging with more cubic
inches.
--
Jim in NC

  #106  
Old May 26th 05, 12:00 AM
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On Wed, 25 May 2005 09:37:53 -0500, Don Stauffer
wrote:

wrote:


One BIG factor is being forgotten here. The diesel is turboed. This
makes it roughly equivalent to an 8 liter engine at about 6psi boost.
Any combustion engine produces power in proportion to the amount of
air consumed. On a diesel it does not necessarily "consume" all the
air that goes through it - but the maximum power output is definitely
limitted by how much air can be put through it. A turbo can eisily
double the amount of air an engine pumps through it at a given speed.

Running an engine at double the speed also increases the amount of air
going through the engine - not quite double due to reduced volumetric
efficiency at speed.

Double the CFM gives double the horsepower, before factoring in
frictional losses and / or pumping losses.

A naturally aspirated diesel engine generally produces less HP per
unit of displacement, but more torque at low RPMs due in part to less
pumping loss (no air throttle)

SOME diesels are turboed. Many are not. Some Diesels are normally
aspirated. Some are supercharged with geared chargers. Some are
turboed. It is by far an overgeneralization to claim that all Diesels
are supercharged, even more so to say they are all turbo-supercharged.



The post being replied to was comparing a turbo cummins to a gas
engine.

Nobody ever said all diesels are turboed.
  #107  
Old May 26th 05, 02:35 PM
Don Stauffer
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Philippe wrote:
Don Stauffer wrote:





SOME diesels are turboed. Many are not. Some Diesels are normally
aspirated. Some are supercharged with geared chargers. Some are
turboed. It is by far an overgeneralization to claim that all Diesels
are supercharged, even more so to say they are all turbo-supercharged.



You forgot supercharged plus turbocharged
http://www.wilksch.com/


I know of some SI engines (aircraft engines) that have both geared and
turbochargers, but not any Diesels. Which Diesels are two-staged?
  #108  
Old May 26th 05, 08:55 PM
Steve
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Morgans wrote:

"Steve" wrote


I believe that if you look at modern diesels currently being produced
and sold, you'll find virtually NONE rated at more than 50-60 horsepower
that are not turbo-supercharged. And equally few that are strictly
mechanically blown (the Detroit Diesel 2-strokes are no longer in
production). The VAST majority are, indeed, turbo-supercharged.



Not true of some of our school busses that were produced in the past 5 or so
years. They make up for the lack of super or turbocharging with more cubic
inches.


I say AGAIN... what percentage of the market is that? Tiny. And they
only TRY to make up with more cubic inches- a DT466E would run rings
around them.
  #109  
Old May 26th 05, 11:17 PM
Morgans
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"Steve" wrote

I say AGAIN... what percentage of the market is that? Tiny. And they
only TRY to make up with more cubic inches- a DT466E would run rings
around them.


I was not taking issue with the tiny percentage concept. I did take issue
with the following, and the NONE

I believe that if you look at modern diesels currently being produced
and sold, you'll find virtually NONE rated at more than 50-60 horsepower
that are not turbo-supercharged.


Not a big deal to me, one way or the other. I always found the non turbo
buses under powered, compared to their turbo brothers.
--
Jim in NC

  #110  
Old July 8th 05, 01:59 PM
Sport Pilot
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mastic wrote:
Bryan Martin wrote:

Not so. In the Otto cycle, the fuel and air are introduced to the cylinder
during the intake stroke. In the Diesel cycle only the air is introduce to
the cylinder during the intake stroke, the fuel in injected at the end of
the compression stroke.


Wrong. Mr Otto invented the four stroke cycle and it is named after
him. The fuel or when it's introduced has nothing to do with it, Otto
refers to the cycle.


SO? He didn't mention fuel in the part you snipped. Diesel is a
differant cycle named after Mr. Diesel.

 




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