2-stroke diesel is the (near) future?

Steve wrote:
Sport Pilot wrote:


Diesel fuel is not conducive to high speed running. Nor is a long
injection period through much of the expansion phase. Yes you can
boost the turbocharger and the other things, but an Otto cycle
engine
will respond with even higher speeds. Parts failure from speed is
not
a problem with diesel engines, the rotating parts have to be bigger
than an otto engine because of the higher compression, yet the otto
engine will turn higer RPM's with smaller parts.



All of the above is true in the common practice of diesel design, but

none of it is necessarily true. There is nothing FUNDAMENTAL that
limits
a diesel to low-RPM designs only. One can build a screaming high-RPM
diesel with light-weight rotating parts, but one would have to ask
"why?" Gasoline engines are made high-revving in order to increase
power
output from a small package, but diesels can develop a lot more
low-RPM
torque through high boost because they don't detonate when "lugged,"
so
there's no NEED to make them scream. If you need more power, don't
spin
them faster, just boost them harder. High RPM is an aggravation, not
an
advantage (no matter what Honda VTEC drivers think...).


Actually diesels don't really deliver that much torque at similar
speeds. Ok they do but only because the valving is timed for the
slower speeds. Many gasoline tractor engines will diliver similar
torque, but with a higher fuel consumption due to the lower compression
ratio. Diesel fuel burns slower and will knock when the injection
timing is shortened to allow higher speeds.

Sport Pilot wrote:

Steve wrote:

Sport Pilot wrote:



Diesel fuel is not conducive to high speed running. Nor is a long
injection period through much of the expansion phase. Yes you can
boost the turbocharger and the other things, but an Otto cycle

engine

will respond with even higher speeds. Parts failure from speed is

not

a problem with diesel engines, the rotating parts have to be bigger
than an otto engine because of the higher compression, yet the otto
engine will turn higer RPM's with smaller parts.



All of the above is true in the common practice of diesel design, but


none of it is necessarily true. There is nothing FUNDAMENTAL that

limits

a diesel to low-RPM designs only. One can build a screaming high-RPM
diesel with light-weight rotating parts, but one would have to ask
"why?" Gasoline engines are made high-revving in order to increase

power

output from a small package, but diesels can develop a lot more

low-RPM

torque through high boost because they don't detonate when "lugged,"

so

there's no NEED to make them scream. If you need more power, don't

spin

them faster, just boost them harder. High RPM is an aggravation, not

an

advantage (no matter what Honda VTEC drivers think...).



Actually diesels don't really deliver that much torque at similar
speeds. Ok they do but only because the valving is timed for the
slower speeds. Many gasoline tractor engines will diliver similar
torque, but with a higher fuel consumption due to the lower compression
ratio.

It depends on what you're comparing to. A lot of tractors use
normally-aspirated indirect-injection diesels, which are no comparison
to a turbocharged diesel. Or to a good normally-asipirated gasoline
engine, except in terms of longevity. Gasoline engines are hard to beat
for the *width* of their torque curve, but modern turbo-diesels do a
good job against them, and do so with better efficiency.

Diesel fuel burns slower and will knock when the injection
timing is shortened to allow higher speeds.


Higher speed requires more than just rapid injection, it also demands
higher boost pressure, which causes the fuel to burn faster without any
knock-like phenomenon. All serious diesels are turbocharged for that
reason (as well as others), and normally-aspirated diesels are limited
to very small power outputs and relatively low efficiency. You can only
get so much combustion chamber pressure through the compression ratio of
the engine- the rest has to come from forced induction. As someone
pointed out earlier, the VW TDI develops power up to 4500 RPM, which is
comparable to many gasoline engines, but it is able to do so only
because it is a turbo-diesel. As I said before, there's no reason that
building a 7000-RPM diesel isn't possible, but there's no REASON to
build one.

On 16 May 2005 11:01:36 -0700, "Sport Pilot"
wrote:


Steve wrote:
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.


Diesel fuel is not conducive to high speed running. Nor is a long
injection period through much of the expansion phase. Yes you can
boost the turbocharger and the other things, but an Otto cycle engine
will respond with even higher speeds. Parts failure from speed is not
a problem with diesel engines, the rotating parts have to be bigger
than an otto engine because of the higher compression, yet the otto
engine will turn higer RPM's with smaller parts.


Ever seen a "super modified" pulling tractor???
I think, from the sound of one at full tilt, that 9000 RPM would be on
the low side - turboed, and sometimes also supercharged
(turbo-compounded) they scream like a wildcat in heat.

"Steve" wrote

In practical terms, no one really
wants or needs a 9000 RPM diesel, though.

Oh, I don't know. NASCAR might be interested in going diesel ! g
--
Jim in NC

wrote:
On 16 May 2005 11:01:36 -0700, "Sport Pilot"
wrote:


Steve wrote:
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.


Diesel fuel is not conducive to high speed running. Nor is a long
injection period through much of the expansion phase. Yes you can
boost the turbocharger and the other things, but an Otto cycle
engine
will respond with even higher speeds. Parts failure from speed is
not
a problem with diesel engines, the rotating parts have to be bigger
than an otto engine because of the higher compression, yet the otto
engine will turn higer RPM's with smaller parts.


Ever seen a "super modified" pulling tractor???
I think, from the sound of one at full tilt, that 9000 RPM would be
on
the low side - turboed, and sometimes also supercharged
(turbo-compounded) they scream like a wildcat in heat.


Compare that maximum to the gasoline maximum. Formula 1 cars will
exceed 20,000 RPM.

Steve wrote:

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.

Actually, detonation can and does occur in Diesels. With today's Diesel
fuels and injection methods the fuel does not burn INSTANTLY upon
injection. The droplets are too large. The droplets tend to evaporate
from their surface area. It IS possible for unburned gases evaporated
from the fuel to exist in the chamber and detonate in local regions. The
effect is nowhere as severe as the detonation that occurs in spark
engines at times. Interesting traces made with high frequency pressure
sensors indicate these local "peaks" in combustion pressure when this
occurs. It is the cause of the "tinkling" sound that Diesels
occasionally make.

Detonation is not a full or nothing situation. Local regions can
undergo detonation even while the majority of the charge undergoes
normal wavefront burning, in either Diesel or SI.

Steve wrote:
Sport Pilot wrote:


Diesel fuel is not conducive to high speed running. Nor is a long
injection period through much of the expansion phase. Yes you can
boost the turbocharger and the other things, but an Otto cycle engine
will respond with even higher speeds. Parts failure from speed is not
a problem with diesel engines, the rotating parts have to be bigger
than an otto engine because of the higher compression, yet the otto
engine will turn higer RPM's with smaller parts.



All of the above is true in the common practice of diesel design, but
none of it is necessarily true. There is nothing FUNDAMENTAL that limits
a diesel to low-RPM designs only. One can build a screaming high-RPM
diesel with light-weight rotating parts, but one would have to ask
"why?" Gasoline engines are made high-revving in order to increase power
output from a small package, but diesels can develop a lot more low-RPM
torque through high boost because they don't detonate when "lugged," so
there's no NEED to make them scream. If you need more power, don't spin
them faster, just boost them harder. High RPM is an aggravation, not an
advantage (no matter what Honda VTEC drivers think...).

I would assume that use of hydrogen as a fuel would allow very high rpm
in a Diesel.

Don Stauffer wrote:

Steve wrote:

Sport Pilot wrote:


Diesel fuel is not conducive to high speed running. Nor is a long
injection period through much of the expansion phase. Yes you can
boost the turbocharger and the other things, but an Otto cycle engine
will respond with even higher speeds. Parts failure from speed is not
a problem with diesel engines, the rotating parts have to be bigger
than an otto engine because of the higher compression, yet the otto
engine will turn higer RPM's with smaller parts.



All of the above is true in the common practice of diesel design, but
none of it is necessarily true. There is nothing FUNDAMENTAL that
limits a diesel to low-RPM designs only. One can build a screaming
high-RPM diesel with light-weight rotating parts, but one would have
to ask "why?" Gasoline engines are made high-revving in order to
increase power output from a small package, but diesels can develop a
lot more low-RPM torque through high boost because they don't detonate
when "lugged," so there's no NEED to make them scream. If you need
more power, don't spin them faster, just boost them harder. High RPM
is an aggravation, not an advantage (no matter what Honda VTEC drivers
think...).

I would assume that use of hydrogen as a fuel would allow very high rpm
in a Diesel.

But no one has come up with a completely satisfactory way to do direct
injection with a gaseous fuel, which is the same problem diesels that
run on natural gas face.

NG diesels are interesting beasts. They actually mix the gas with the
intake air and compress it like a spark-ignition engine would, setting
up the possibility of detonation, but since NG is has a very high
relative "octane" rating, it doesn't ignite until a *tiny* shot of
diesel is injected to initiate combustion. They do have to operate at
somewhat lower compression than a straight diesel, but its still in the
neighborhood of 14:1 or 15:1 which is much higher than you can achieve
with gasoline, at least on any fuel short of leaded aviation racing fuel
that is brewed up in ridiculously small (and expensive) quantities for
the Reno air racers.

The OTHER Kevin in San Diego wrote:
On Mon, 16 May 2005 15:08:37 -0500, Steve wrote:


High RPM is an aggravation, not an
advantage (no matter what Honda VTEC drivers think...).


Shhhh.. Don't tell the guys at Pratt & Whitney that...

It depends... gas generator shafts need to spin fast, but the LP spool
on a PW4000 doesn't turn any faster than the engine in my car

We own a 2003 Jetta TDI and it poops out before it gets to 4500. However, it
goes uphill at 80mph gaining speed at around 2500RPM. BTW. Hp= Torque X
RPM. If your 100hp engine peaks at 2500 rpm and your 200horse engine peaks
at 7500 rpm, the 100hp engine has to develop 1.5 times more torque than your
200hp engine at the peak hp rpm.

--
Stuart Fields
Experimental Helo magazine
P. O. Box 1585
Inyokern, CA 93527
(760) 377-4478
(760) 408-9747 general and layout cell
(760) 608-1299 technical and advertising cell

www.vkss.com
www.experimentalhelo.com


"Steve" wrote in message
...
Sport Pilot wrote:

Steve wrote:

Sport Pilot wrote:



Diesel fuel is not conducive to high speed running. Nor is a long
injection period through much of the expansion phase. Yes you can
boost the turbocharger and the other things, but an Otto cycle

engine

will respond with even higher speeds. Parts failure from speed is

not

a problem with diesel engines, the rotating parts have to be bigger
than an otto engine because of the higher compression, yet the otto
engine will turn higer RPM's with smaller parts.



All of the above is true in the common practice of diesel design, but


none of it is necessarily true. There is nothing FUNDAMENTAL that

limits

a diesel to low-RPM designs only. One can build a screaming high-RPM
diesel with light-weight rotating parts, but one would have to ask
"why?" Gasoline engines are made high-revving in order to increase

power

output from a small package, but diesels can develop a lot more

low-RPM

torque through high boost because they don't detonate when "lugged,"

so

there's no NEED to make them scream. If you need more power, don't

spin

them faster, just boost them harder. High RPM is an aggravation, not

an

advantage (no matter what Honda VTEC drivers think...).



Actually diesels don't really deliver that much torque at similar
speeds. Ok they do but only because the valving is timed for the
slower speeds. Many gasoline tractor engines will diliver similar
torque, but with a higher fuel consumption due to the lower compression
ratio.

It depends on what you're comparing to. A lot of tractors use
normally-aspirated indirect-injection diesels, which are no comparison
to a turbocharged diesel. Or to a good normally-asipirated gasoline
engine, except in terms of longevity. Gasoline engines are hard to beat
for the *width* of their torque curve, but modern turbo-diesels do a
good job against them, and do so with better efficiency.

Diesel fuel burns slower and will knock when the injection
timing is shortened to allow higher speeds.


Higher speed requires more than just rapid injection, it also demands
higher boost pressure, which causes the fuel to burn faster without any
knock-like phenomenon. All serious diesels are turbocharged for that
reason (as well as others), and normally-aspirated diesels are limited
to very small power outputs and relatively low efficiency. You can only
get so much combustion chamber pressure through the compression ratio of
the engine- the rest has to come from forced induction. As someone
pointed out earlier, the VW TDI develops power up to 4500 RPM, which is
comparable to many gasoline engines, but it is able to do so only
because it is a turbo-diesel. As I said before, there's no reason that
building a 7000-RPM diesel isn't possible, but there's no REASON to
build one.