Author Topic: 2-stroke piston window, rear boost port.  (Read 46809 times)

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Offline djr

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Re: 2-stroke piston window, rear boost port.
« Reply #30 on: January 30, 2015, 08:27:29 pm »


There is never going to be high enough pressure in the crankcase to 'push" intake out the transfers especialy on a running engine.

If the pressure in the crankcase isn't greater than the pressure in the cylinder it is a pysical impossibility for the motor to ever run, simple physics. I didn't need to spend 4 years at UNI to work that one out.

That makes sense ,

I have a lot to learn about  2 strokes ,  so far Sleepy & Daryl Jones explanations seem the most logical, but its all interesting anyway.
thanks

Offline Momus

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Re: 2-stroke piston window, rear boost port.
« Reply #31 on: January 30, 2015, 09:07:32 pm »
Quote from: Lozza
There is never going to be high enough pressure in the crankcase to 'push" intake out the transfers especialy on a running engine.

I reckon any good 2 stroke on the bugle is going to have a net positive pressure in the cases and an inertia ram effect from column flowing through the carb and intake tract.
Of course the case pressure only has to be slightly higher than the depression in the cylinder caused by the exhaust to be net positive
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Offline David Lahey

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Re: 2-stroke piston window, rear boost port.
« Reply #32 on: January 30, 2015, 10:08:25 pm »
I'm loving this topic
previous pseudonym feetupfun

Offline Daryl Jones

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Re: 2-stroke piston window, rear boost port.
« Reply #33 on: January 31, 2015, 12:02:29 am »
OK, I think I've finally got it.

Now, I just need some substantial funding for R&D, and the patent lawyers costs.

  Four stroke style, lubricated bottom end, (No nasty 2 stroke smoke).
  Simple barrel with an exhaust port and multiple reed valved inlets, (where the transfers used to be),
  Multi-point Fueling system (Injection would be nice).
  Inlet manifolds of appropriate length and volume to allow 'harmonic resonance'.
  'Suitable' expansion chamber exhaust.

Oh! And a decent Starter, to wind it up to a minor harmonic speed, say 5,000 rpm, before introducing the fuel & ignition.

I have created a "pulse jet" engine which uses the piston to extract some energy from the pressure pulses above it.

The pressure pulses below it below it are sort of wasted, unless you direct the crankcase venting through another pair of reeds into the intake side.
(No patent for that bit, it's been done plenty of times already).

I really can't believe that no-one has done something like this already.   
Okay, Detroit Diesel 2-strokes do, but then they messed up the beautiful simplicity of this idea, by using dirty great superchargers to Pump the air into the cylinders. Obviously, lacking in imagination.

Get in early, while the shares are still cheap.

Cheers, DJ.
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Offline Momus

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Re: 2-stroke piston window, rear boost port.
« Reply #34 on: January 31, 2015, 12:37:45 am »
Quote from: Daryl Jones
Get in early, while the shares are still cheap.

Ya.

What is Sarich worth these days; 700 plus million?


« Last Edit: January 31, 2015, 12:46:37 am by Momus »
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Offline djr

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Re: 2-stroke piston window, rear boost port.
« Reply #35 on: January 31, 2015, 03:31:21 am »
I try to be open minded, listen to new ideas & opinions,
but I am struggling to believe the LOZZA 2 stroke theory -

"there is never going to be high enough pressure in the crankcase to push intake out of the transfers especially on a running engine"
"no case compression is needed to start an engine"
"all the work is done by the pipe at BDC"

If all of these things are true then it must be IMPOSSIBLE for a 2 stroke to start & run with its exhaust removed.

well I just went out to the shed and took the complete exhaust off my old DT175, gave it a few kicks and it started up and runs !
surely this is impossible because "all the work is done by the pipe at BDC" and "there is never going to be enough pressure in the crankcase to push intake out of the transfers especially on a running engine"

can someone explain this  :)

Offline John Orchard

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Re: 2-stroke piston window, rear boost port.
« Reply #36 on: January 31, 2015, 07:55:41 am »
Well on my CR500 you can feel the crankcase compression through the kickstart lever, take the head off and push the kick lever down, you can feel the kick lever getting over the primary compression, you can hear the 'pop' from the sudden pressure escaping from the crankcase to above the piston as the transfers open.
Johnny O - Tahition_Red factory rider.

Offline Lozza

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Re: 2-stroke piston window, rear boost port.
« Reply #37 on: January 31, 2015, 11:42:24 am »


There is never going to be high enough pressure in the crankcase to 'push" intake out the transfers especialy on a running engine.

If the pressure in the crankcase isn't greater than the pressure in the cylinder it is a pysical impossibility for the motor to ever run, simple physics. I didn't need to spend 4 years at UNI to work that one out.
connect a pressure transducer to the crankcase like Robert Fleck did and you see that the pressure in the case is only ever higher in a STATIC state. In a DYNAMIC ie the engine running pressure in the crankcase is never higher than the cylinder. Maybe yamaha got it all wrong  when they realised that and changed the yzr250. Oliver Jacque is glad they did though.
Jesus only loves two strokes

Offline Lozza

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Re: 2-stroke piston window, rear boost port.
« Reply #38 on: January 31, 2015, 11:44:08 am »
I try to be open minded, listen to new ideas & opinions,
but I am struggling to believe the LOZZA 2 stroke theory -

"there is never going to be high enough pressure in the crankcase to push intake out of the transfers especially on a running engine"
"no case compression is needed to start an engine"
"all the work is done by the pipe at BDC"

If all of these things are true then it must be IMPOSSIBLE for a 2 stroke to start & run with its exhaust removed.

well I just went out to the shed and took the complete exhaust off my old DT175, gave it a few kicks and it started up and runs !
surely this is impossible because "all the work is done by the pipe at BDC" and "there is never going to be enough pressure in the crankcase to push intake out of the transfers especially on a running engine"

can someone explain this  :)
at no stage ever did I say an engine is impossible to start without the pipe
Jesus only loves two strokes

Offline Lozza

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Re: 2-stroke piston window, rear boost port.
« Reply #39 on: January 31, 2015, 11:45:21 am »
Well on my CR500 you can feel the crankcase compression through the kickstart lever, take the head off and push the kick lever down, you can feel the kick lever getting over the primary compression, you can hear the 'pop' from the sudden pressure escaping from the crankcase to above the piston as the transfers open.
Thats not with the engine running is it
Jesus only loves two strokes

Offline sleepy

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Re: 2-stroke piston window, rear boost port.
« Reply #40 on: January 31, 2015, 12:26:33 pm »


There is never going to be high enough pressure in the crankcase to 'push" intake out the transfers especialy on a running engine.

If the pressure in the crankcase isn't greater than the pressure in the cylinder it is a pysical impossibility for the motor to ever run, simple physics. I didn't need to spend 4 years at UNI to work that one out.
connect a pressure transducer to the crankcase like Robert Fleck did and you see that the pressure in the case is only ever higher in a STATIC state. In a DYNAMIC ie the engine running pressure in the crankcase is never higher than the cylinder. Maybe yamaha got it all wrong  when they realised that and changed the yzr250. Oliver Jacque is glad they did though.

Sounds like BS to me. Prove it by posting a link to their research paper or publish your own finding from all the dyno work you have done with pressure transducers so that myself and the other mechanical engineers on this forum can re-learn all the thermodynamic theory that we have been taught.

Offline djr

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Re: 2-stroke piston window, rear boost port.
« Reply #41 on: January 31, 2015, 08:17:54 pm »
I try to be open minded, listen to new ideas & opinions,
but I am struggling to believe the LOZZA 2 stroke theory -

"there is never going to be high enough pressure in the crankcase to push intake out of the transfers especially on a running engine"
"no case compression is needed to start an engine"
"all the work is done by the pipe at BDC"

If all of these things are true then it must be IMPOSSIBLE for a 2 stroke to start & run with its exhaust removed.

well I just went out to the shed and took the complete exhaust off my old DT175, gave it a few kicks and it started up and runs !
surely this is impossible because "all the work is done by the pipe at BDC" and "there is never going to be enough pressure in the crankcase to push intake out of the transfers especially on a running engine"

can someone explain this  :)
at no stage ever did I say an engine is impossible to start without the pipe
Lozza , YOUR THEORY says its impossible for the engine to start without the pipe.
 Because you state that " ALL the work is done by the pipe at BDC "
 if you had said "SOME of the work is done by pipe at BDC" or even "MOST of the work is done by the pipe at BDC" then it would still be  possible for the engine to run without the pipe.
 But if the pipe is doing "ALL the work" then surely the engine cant run without the exhaust fitted,
because you also state that " there is never going to be high enough pressure in the crankcase  to push intake out of the transfers"
without the pipe fitted how then does any air/fuel get into the cylinder if its not from crankcase compression ?

Offline Daryl Jones

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Re: 2-stroke piston window, rear boost port.
« Reply #42 on: January 31, 2015, 09:10:21 pm »
This is from the DYNOmite Forum.  They make engine transducer and data recording kits.

I suspect that they know more than just a little bit about these measurements!
The coloured and resized text is my work.

Link here: http://forums.land-and-sea.com/showthread.php?t=64

2-stroke crankcase pressures
________________________________________
How should I set up to measure pressures in my snowmobile’s crankcase? I already have the -12 to 22 PSI manifold pressure sensors but it seems to read rather erratically.
  #2   
 07-05-2005, 08:49 AM
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Land & Sea Engineering       Join Date: Mar 2004
Location: Concord, NH
Posts: 210

Re: 2-stroke crankcase pressures
________________________________________
1) If you are trying to map the cyclical crankcase pressure changes that occur during each revolution of the crankshaft, you need more than just your sensor. This requires the same type of equipment and software Option Pack as combustion chamber pressuring mapping.

Our DYNOmite-Pro boards collect data at either 200 Hertz or 1,000 Hz (in USB mode). This is ideal for traditional dynomometer testing - where you are collecting data on Hp, Torque, RPM, fuel flow, etc. But, to map what goes on during a single revolution of the engine, you'll need individual data readings taken consecutively at each degree of crankshaft rotation. At high (two-cycle range) RPM's we are talking about board sets that can handle over 100,000 Hertz - like the 500,000 Hz board found in our Combustion Pressuring Mapping Kit.

You also need an encoder that provides an index for each pressure reading (to the exact degree position of the crankshaft when that data is captured). Again, the encoder in the Combustion Pressuring Mapping Kit is appropriate.
Note: It's mounting (which is designed for an automotive crankshaft dampener) would have to be custom adapted to your magneto housing.

Lastly, you will want to custom order the kit with a much lower range pressure transducer. Instead of the normal 2,000 PSI range, you will want one that is appropriate for the -14 to +30 PSI readings of a normally aspirated two-stroke's crankcase.


2) If instead all you want is to monitor the average crankcase pressure (a relatively low positive number), then your existing sensor can do that. However, you can not just screw the sensor into the crankcase. Those erratic readings are caused by the arbitrary synchronization aliasing) between your DYNOmite's 200 Hz sampling rate and the position of your engine's crankshaft. You're never taking the pressure readings at the same index twice.

Instead, plumb it to your engine's crankcase using a restricted dampening orifice. A hose with about a 0.030" fuel jet stuck in it works well as the orifice. Also, put a small dampening chamber (plenum) between the orifice and your pressure sensor. A small in-line fuel filter makes a convenient chamber. Once your have the restrictor and plenum in place I think you will find your erratic readings cured.

Note: We recommend that the pressure sensor be oriented so any residual fuel droplets will gravity drain back into the plenum and crankcase between tests. That greatly extends the sensor's life.
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Offline Tomas

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Re: 2-stroke piston window, rear boost port.
« Reply #43 on: January 31, 2015, 10:11:53 pm »
positive/ negative pressure, even minimal, is needed to move fresh charge/mixture through the engine.
block your intake, pressure drops/stops fresh mixture is not geting into combustion chamber- engine will stop
block your exhaust ,pressure builds up and over power intake pressure and stops fresh mixture from reaching combustion chamber- engine will stop
so, yes there is pressure inside crankcase/motor that moves fresh fuel mixture around
various modifications of engine parts can improve/change this.
you can not start an engine simply by spraing fuel mixture into it. pressure in various form is  is needed to start it.



Offline pokey

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Re: 2-stroke piston window, rear boost port.
« Reply #44 on: January 31, 2015, 10:32:28 pm »
Woo. seems like the hard way of going about something when you can use what you already know

if a bottom end has bad seals  it runs like crap. the fact it has seals says it has some pressure but just how much?

When you pressure test a bottom end most manufacturers state it needs to hold the pressure of 6 - 15 psi for 5 minutes(most say 6). and vacuum of 5-7 inches of mercury for the same time..
 To my mind thats sfa in the bottom end  and its not rocket science.

ergo the crank case does play a bit of a part but something else is doing the big work.

try sticking a CR125pipe on a bog stock MT125 and it will give you the clues.