2-stroke diesel is the (near) future?

wrote:

"Steve" wrote in message
...


I pretty much agree, although today's high-speed diesels are doing a lot
better at approchin the constant-enthalpy cycle than they used to,
thanks to being able to divorce the injection profile from crankshaft
position via electronically-controlled injection systems.


Now that you mentioned it, what sort of rpm ranges are the high speed
diesels capable of?

Well, a "high speed" diesel in the usual sense is anything that turns
more than 1500-2000 RPM. So 18-wheeler diesels (Cummins N-14, DD Series
60, etc) are considered "high speed diesels" and locomotive engines are
'medium speed." Low-speed diesels are those direct-drive 3-story tall
ship engines that turn 120 RPM max and put out 25,000 horsepower.

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.

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

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

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

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.

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.

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...).

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.

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.