2-stroke diesel is the (near) future?

Steve wrote:
> The litmus test for me is whether or not fuel is present in the cylinder
> at the start of the compression stroke. If the fuel is already there,
> and is ignited either by a spark, a glow plug/hot head, or even a
> "pilot" injection of diesel as in a CNG "diesel" engine, then its not
> running in a true diesel combustion mode.
>
> The true diesel cycle achieves its approximation of constant-pressure
> expansion by gradually (relative to the piston speed- its actually very
> fast) injecting the fuel AS the piston moves down.
>

While I do not object to this thread myself, others may find it going
off-topic. I would like to invite everyone interested in these kinds of
discussions to look at the heat engine discussion group, a Yahoo group.
It is a discussion group for any discussion on any type of heat engine,
and I'd love to see more discussions of this type on it. Go to Yahoo,
select "groups" and search for "heat engine"

Don

Steve wrote:
> Sport Pilot wrote:
>
> The model
>
>> diesel engines will not turn as fast as the gas or methanol/nitro
>> engines because the fuel (ether and kerosene) will not burn as fast.
>
>
>
> I say again: there is no magic rule that says "diesel burns slower" than
> gasoline. Increasing the boost pressure can increase the burn rate AS
> MUCH AS YOU WANT. Its just not done most of the time, because no one
> WANTS a 7000 RPM engine when a 4000 RPM engine is available to do the
> same job. People only build 7000 RPM engines when there's no other way
> to get the power.
>
Hydrogen, for example, is a very rapid burning fuel. Hydrogen can and
has been used in Diesels. I also suspect that natural gas, another
common diesel fuel, burns at a high rate. The slow burn rate with many
liquid diesel fuels is due to the time it takes the surface area of the
droplets to vaporize.

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.

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/


--
Pub: http://www.slowfood.fr/france
Philippe Vessaire Ò¿Ó¬

Thomas Tornblom wrote:

> Steve > writes:
>
>
>>Sport Pilot wrote:
>>
>>
>>>Why the obvious apple and orange comparision?
>>
>>
>>To refute the statement that "more speed is more power."
>>
>>
>>> You need to compare engines of equal size.
>>
>>
>>OK, Lets do it!
>>
>>Dodge 5.9 Liter v8 gasoline engine: 230 horsepower at ~5000 RPM
>>
>>Compared to:
>>
>>Dodge/Cummins 5.9 Liter turbo-diesel engine: 325 horsepower at 2900 RPM
>>
>>
>>More speed is NOT more power any more than more torque at the same
>>speed is more power.
>
>
> uh?

huh. Read it again.

>
> 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.

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.

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.

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

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.

"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