Crank Case Pressure/Vacuum Theory

[Termitebuffet]

That was no carb at all

Sawhawgz, ruining the internet since 2012...

You can hear me raising and lowering rpm on the drill too...

Sawhawgz, ruining the internet since 2012...

 

[Fruecrue]

You can hear me raising and lowering rpm on the drill too...

Sawhawgz, ruining the internet since 2012...

Tough to see on video, did the peak reading stay the same?

 

[Termitebuffet]

Tough to see on video, did the peak reading stay the same?

I was hoping to see it better on the video. ...

Sawhawgz, ruining the internet since 2012...

 

[XP_Slinger]

Hard to tell but it looks like the blur of the needle gets wider as speed increases. I’ll try to get a slow motion video tomorrow.

 

[RIDE-RED 350r]

I'm gonna go out on a limb and say impulse gets stronger with RPM. Think of it this way, as the piston speeds up, it's going to trap more case compression as it begins to move down from TDC. Think of an airplane propeller. It generates more thrust the faster it spins. Moving slowly it barely generates thrust. It has to rotate faster to generate enough thrust to move the aircraft. As the piston first begins to move down after TDC, it's already starting to build case compression before the piston closes the intake port. The speed in which the piston travels is faster than that volume can escape back out the intake port, to a point. I'm sure a little bit is lost, but most is retained or else there would be terrible spit back. Obviously Reed valves are needed as port timing layouts get more aggressive and don't rely on the piston skirt to time intake. This allows for intake to take full advantage of the full range of the piston stroke..

IDK if any of that makes any sense...

Anyway, I say impulse increases by some amount as RPM increases. How much, I don't know. And Im thinking there is a point at which no more is gained as RPM continues to increase. Max efficiency is achieved

Thoughts??

 

[Termitebuffet]

I might have a lower pressure gauge I can try...it seems to me by watching the video that it didn't change /with speed....but it's hard to tell

Sawhawgz, ruining the internet since 2012...

 

[RIDE-RED 350r]

My guess is that it would have to be measured electronically to be measured accurately

 

[fossil]

Might be worth a try a timing light in line with the plug. Attach light, ground plug and fire it a the gauge.
I used strobes a lot at work on high speed equipment to watch what was happening during the process.

Not sure what the max cps on them is now but wouldn't it be great if a clever machinist could put a plexiglass plug in a pump side carb cover over the diaphragm flaps and slow motion it at high rpm with the saw running,

 

[Marshy]

Looked to me in @chy_farm tests that pulse and piston are 1 to 1.
I think the gauge reading is misleading. The sine wave so to speak isn’t equal above and below the zero point so we see the needle seem to settle high.
Impulse tapping in the crankcase must play a role as does intake port timing.

I mostly made all that up on the fly.
How’d I do?

Since I’m making chit up, I’d also like to challenge the theory of @Termitebuffet that pulse strength is constant regardless of engine speed.
My minds eye sees a change due to mass air flow. If the throttle plate restricts intake, wouldn’t there be less primary compression, thus a change in impulse strength?

In my opinion, the intake pulse is only slightly below atmospheric and the primary compression pulse is significantly more. The gauge cant react fast enough to show the real pressure differences taking place.

 

[CR888]

Why does it matter what strength the impulse has when running @WOT?

 

[retro]

Y'alls brains might be getting all squirmy when ya keep hearing this... (thanks for this separate thread!)... but the single answer to all of your questions (and your tests also demonstrate this) is still the same:

Atmospheric air pressure is performing all of the work required to initiate, maintain and to cease, all movements of air and fuel into all fueled heat motors/engines.

It is a pre-existing natural force. It is a relatively constant force (assuming your elevation is held relatively constant). And it is the only already existing force available on earth for us to take advantage of, in fueled heat motor development. It exerts its force (causing movements) on pressure gauges, diaphragms, pistons, valves, fuel (both inside and outside of fuel tanks), and its force effects the latent heat properties of gases and liquids and effects the rate of vaporization (vapor pressure) of liquid fuels to list just a few.

You see, if we had to create a force ourselves, to supply a fueled heat motor its basic aspiration needs to function, such a device would consume more energy than it could create. Thats perpetual motion or free energy crap... and no one has ever pulled that trick off on earth.

So in short, atmospheric air pressure provides us the only force for a fueled motor to be functional and it is responsible for everything at all times for aspirating an ICE.

 

[retro]

The pulse signal in the crankcase alternates 1:1 with the movement of the piston in an idealized example. Port timing/duration events optimize filling and emptying for a certain RPM target though. Because a stationary mass tends to remain stationary... while mass in motion tends to remain in motion. Energy (time) is required to alter movement.

A motor produces its peak torque at an RPM where both filling and emptying efficiencies are most optimal.

EDIT: Actually there is a lot more to that... the gas exchange process consists of a complex interdependent set of events, but lets keep this basic and simple and to the point of this thread?

 

[wcorey]

Y'alls brains might be getting all squirmy when ya keep hearing this... (thanks for this separate thread!)... but the single answer to all of your questions (and your tests also demonstrate this) is still the same:

Atmospheric air pressure is performing all of the work required to initiate, maintain and to cease, all movements of air and fuel into all fueled heat motors/engines.

It is a pre-existing natural force. It is a relatively constant force (assuming your elevation is held relatively constant). And it is the only already existing force available on earth for us to take advantage of, in fueled heat motor development. It exerts its force (causing movements) on pressure gauges, diaphragms, pistons, valves, fuel (both inside and outside of fuel tanks), and its force effects the latent heat properties of gases and liquids and effects the rate of vaporization (vapor pressure) of liquid fuels to list just a few.

You see, if we had to create a force ourselves, to supply a fueled heat motor its basic aspiration needs to function, such a device would consume more energy than it could create. Thats perpetual motion or free energy crap... and no one has ever pulled that trick off on earth.

So in short, atmospheric air pressure provides us the only force for a fueled motor to be functional and it is responsible for everything at all times for aspirating an ICE.

You make it sound as though a crank and piston aren't even required to take advantage of this phenomena.
But in this case atmospheric pressure is much like torque, it's just a stationary force that does no work until a mass is set in motion to rotate/reciprocate both against and with it.

 

[retro]

You make it sound as though a crank and piston aren't even required to take advantage of this phenomena.
But in this case atmospheric pressure is much like torque, it's just a stationary force that does no work until a mass is set in motion to rotate/reciprocate both against and with it.

I didn't mean to say that... a crank and piston provide the mechanical means for us to take advantage of and harness atmospheric air pressure. In other words, they are tools.... Tools used to exploit that force to produce rotary energy.

But yeah, until that force is taken advantage of, it produces nothing.

 

[retro]

You'd find it impossible to operate a chainsaw motor outside of earths atmosphere no matter how much air and fuel you provided, due to the lack of an existing, sufficient pressure.

So, what would happen if you brought along a positive displacement blower and installed it on a chainsaw motor (in an effort to replace your missing atmospheric force) in deep space?

Nothing. The device would require more input power to function than it would output.

 

[wcorey]

Rpm shouldn't change the pressure in my tiny mind

Sawhawgz, ruining the internet since 2012...

My tiny mind agrees. The piston is displacing the same volume regardless of speed.

The speed of the piston/impulse will increase/decrease the volume pumped until/unless it reaches a point where the throughput is restricted, an increase in speed will then result in higher pressure.

 

[wcorey]

So just flutter above and below ...I don't see it being huge

As long as there's a certain range of change/motion, I don't think it matters whether it operates entirely above or below atmospheric pressure, it's just relative.

 

[retro]

The speed of the piston/impulse will increase/decrease the volume pumped until/unless it reaches a point where the throughput is restricted, an increase in speed will then result in higher pressure.

False.

An increase in piston speed (swept feet per second/minute) will correlate 1:1 with the volume of air entering the crankcase until the RPMs reach a point where the port can no longer flow enough air to keep up with the demand. Beyond that RPM point the peak crankcase pressures after compression will be in decline, due to incomplete filling.

Remember, all pressure levels inside the crankcase are characterized and dependent upon the atmospheric pressure level available outside. You'd need to add a blower (increase pressure) if you want a small port to flow more air above that limiting RPM point.

 

[wcorey]

You'd find it impossible to operate a chainsaw motor outside of earths atmosphere no matter how much air and fuel you provided, due to the lack of an existing, sufficient pressure.

Well if as said you provided a supply of air to feed the saw, that air would have to have been contained under pressure, lest it disperse itself evenly across the universe. So there you go...

With pressurized air going in and vacuum without, it would be pretty much supercharged...

 

[retro]

I just realized you were talking about the fuel pump operating. But same as above ^^^