what is "strato charged"

[PES+]

I got it now......



I see now what happened.....Komatsu stated the name from the original concept and the name stuck and has become completely generic.

I did stumble over a very simplified version of how we got where we are today in my travels.

Read this and think next time you wear that Deere John hat

http://money.cnn.com/magazines/fortune/fortune_archive/2002/05/13/322885/index.htm

"The $13-billion-a-year farm machinery giant had come up with a low-emission technology for its Homelite line of two-stroke consumer handheld products, which it had purchased only a few years before. The design, called compression wave, is similar to RedMax's stratified design. What was not similar was the full-court press that Deere's lobbyists put on the EPA to persuade the agency to stick with the more stringent Phase II standards, despite the howling protests of PPEMA. Deere's efforts paid off, as the EPA adopted the tougher standards in July 1999.

But what happened next was bizarre. Although Deere licensed the technology to Stihl, not a single product embodying it has ever reached the market. Last November, moreover, Deere sold the Homelite division to TechTronics Industries (TTI) of Hong Kong. Under a squeeze from big-box retailers, Homelite had lost $100 million in 21 months. Deere has few friends in the handheld industry today. "What's fascinating is that Deere persuaded the EPA, and then the industry gets screwed," says an industry source closely involved with the EPA. Deere won't comment, but in fairness it must be said that its intense lobbying efforts may have incited fresh waves of innovation among the handheld manufacturers. "

Nothing runs like a Deere............

 

[PES+]

Now......

If the Stihl strato does not oxidize the fuel charge at all to complete burning as I mentioned......how did they increase the burn efficiency to such a degree that the layers of air simply force out the completely or nearly completely burned exhaust gases?

Enquiring minds and all that

 

[Stihl #1]

You guys are killing me!!!
First go back and re-read this post, page 2:
http://www.arboristsite.com/showthread.php?p=945266#post945266
Pay attention to the explanation about grams per kilowatt hour (g/kWh) measurement of emissions.

OK, are you back now? But first some history and definitions.

Red Max was the first to offer a Strato-Charged engine as they called it back in 97 or 98, and still do sell their design, which uses reeds in the top of the trasfer ports to let air stack up in the transfer port. On low RPM applications like trimmers and cutoff machines reeds are effective at controlling scavenge loss by putting a little puff of clean filtered air between the air-fuel mix coming in from the crankcase and the burnt exhaust gases that need to be pushed out.
SCAVENGE LOSS: unburned fuel coming in from the crankcase, through the transfer ports, leaking out the open exhaust port before the piston has time to close the port.

See how the red shows the air fuel mix coming in and sweeping back and across to push the exhaust gases (purple) out? That is called loop scavenging. Old two-stroke designs had the transfer ports across from the ex ports, called cross scavenging, and had to have a big tall ridge across the top of the piston to keep all the fuel from going straight out, when the transfer ports were open. It was a straight shot across the top of the piston. Here is a cross scavenge Jacobsen engine, reed induction, about a 3k RPM motor.

This design will not work at high RPM.
Here is a pic of loop scavenging.

See how much fuel is leaking out of a 2 port cylinder? This is called short circuiting and in older engine designs amounted to as much as 1/4 of each tank of fuel leaking out the exhaust port into the air as scavenge loss, or emissions. And this is what the EPA said must be reduced.
Here is a MS 360 cylinder, compared to a MS 361. The MS 361, has four closed ports, compared to the MS 360 it replaces. When measuring the emissions on these two saws, a MS 360 is rated at 121g/kWh, and the completely new design MS 361 is rated at 82 g/kWh. Four port design, along with other design changes, makes a positive impact on lowering emissions, as well as increasing performance and fuel economy.

The MS 361 is still a conventional two-stroke, it is just more efficient at transfer and loop scavenging that it's predecessor. Four ports are better than two to create the loop needed to scavenge out the exhaust gases and not lose as much unburned fuel in the process. Also notice that the transfer ports are longer on the MS 361. That is important in stratified scavenge design.

More to come on the MS 441 stratified scavenge process. And it is stratified and that does mean LAYER!

And maybe later I will do a thread on the compression wave injection design, which is altogether different.

 

[icelation8]

Thats exactly what i was saying you just had access to all those fancy graphics not fair.
lol

 

[PES+]

I'm waiting for the second set of drawings with the layering

And the now defunct OMC would beg to differ about not being able to use deflectors at high RPMs but I digress.......

 

[Stihl #1]

STIHL marketed the FS 83 with a RedMax engine, mainly in CA until the FS 110 was introduced. I think 1999, 2000 was all.

So the EPA said clean up the exhaust. The easiest way is to put a CAT in the muffler, which is just an afterburner and does nothing for power, fuel economy, etc. and just adds weight and cost. But it does do a good job of lowering emissions.
Stratified scavenging addresses the problem in the combustion chamber and results in less scavenge loss of unburned fuel. So the end result is not necessarily a lot more power, but for sure better use of the fuel, so better fuel economy. Put a measured amount of fuel in a MS 440 and a MS 441 and with the same chain, wood and operator the MS 441 will cut longer, maybe even 10 to 20 % longer. At $3.30 a gallon for fuel (here) that is a good reason to buy a MS 411. And let's face it, when was the last time anyone went to a dealer and said they want a new saw that has low emissions? But if it is less thirsty for fuel, then that is a plus.
So the MS 441 has 6 ports in the cylinder. 4 come from the crankcase in the usual manner, they are closed, but they are very long. 2 ports come from the clean air bypass butterfly, and open at the rear of the cylinder just under the rear set of transfer ports. This pic has red for for transfer ports and blue for air intake ports.

Now look at the pockets in the side of the piston.

When the piston is at TDC the pocket opens the 2 fresh air ports up to feed air into the top of all 4 transfer ports to fill them with air. The air is drawn in because as the piston went up it created low pressure in the crankcase, which is also drawing air-fuel mix from the carb through the intake port in the usual manner of a two-stroke. This pic has the piston next to the cylinder in the proper position.

As with any piston ported two-stroke engine the piston is the valve, and in this case it just continues to act as a valve to let air into the transfer ports from the top down. That air stacks up in the long port but never makes it into the crankcase or mixes with the fuel laden air in the crankcase. As soon as the piston starts back down it closes the fresh air ports and the transfer ports and the intake port and starts building pressure in the crankcase. The air is trapped in the transfer ports. Then when the piston goes down far enough on the power stroke to open the exhaust port the exhaust starts flowing out, then the transfer ports open a fraction of a second later and the first thing in is LAYER of clean filtered air that begins the loop scavenge process and pushes out the exhaust gas, and then the fuel air mix comes in just a tiny little bit later. But by then the piston has started back up in the bore and closes the ex port before much of the fuel has escaped.

See how there is a layer of air (blue) between the exhaust (purple) and the fuel air mix (red).
This is stratified scavenging, and expect to see it on just about any new two-stroke engine.
The new 575 Husky and a new RedMax saw that I can't remember the model of is more or less identical in this way. It is not just STIHL doing this.

 

[Stihl #1]

Yes Ice you had it, but pics help. At least it does for this old Aggie!

 

[PES+]

I see a slug of air.....no layering but my mind is usually mush.....

So this theory is simply using the air to clear the spent gases and to hold back the crankcase mixture and has no other effect?

 

[Just Mow]

Yes Ice you had it, but pics help. At least it does for this old Aggie!

HOOK'EM

 

[Stihl #1]

I see a slug of air.....no layering but my mind is usually mush.....

So this theory is simply using the air to clear the spent gases and to hold back the crankcase mixture and has no other effect?

Yes it has a major effect, less scavenge loss of unburned fuel. So lower g/kWh emissions. And better fuel economy. More wood cut on less gas. Money in your pocket. And I would guess that as time goes by and more is understood and new young engineers come along and add their ideas to what has been done allready, it will only get better. How much better is a MS 440 than the saw it replaced?

 

[Stihl #1]

HOOK'EM

no comment

 

[Lakeside53]

I knew it was only matter of time... big thanks to


Stihl#1

 

[Just Mow]

no comment

 

[Just Mow]

I knew it was only matter of time... big thanks to


Stihl#1

 

[Lakeside53]

. And I would guess that as time goes by and more is understood and new young engineers come along and add their ideas to what has been done allready, it will only get better. How much better is a MS 440 than the saw it replaced?

wait.. you're saying old engineers have no new ideas?????


oh.. I get it... we're required to filter the fountain of youthful ideas.. kind of like boat anchors... :greenchainsaw: :greenchainsaw:

 

[PES+]

Could you share the drawings showing the differences to the percussion wave set up?

 

[Stihl #1]

wait.. you're saying old engineers have no new ideas?????


oh.. I get it... we're required to filter the fountain of youthful ideas.. kind of like boat anchors... :greenchainsaw: :greenchainsaw:

Don't start putting words in my mouth, Lake! LOL
But you will agree that sometimes you have given a problem all you have got, and then someone else, maybe younger, maybe not, comes along, and says "try this" and off you go.
I think it will continue to get better as new ideas are tried. I am excited about what is goinf on with these little motors. Like the other thread on "Fascination" it really is fascinating to see what new technology and design will be next.

 

[Stihl #1]

Could you share the drawings showing the differences to the percussion wave set up?

Tomorrow, I am done for the evening. Good night.

 

[PES+]

Thank You in advance

Tomorrow, I am done for the evening. Good night.

Great info

 

[redprospector]

I'm convinced that the "stratocharged" engine will be the saw of the future, just to comply with the EPA. I'll just be glad when tech's understand them so they will run well at altitude. Not trying to be a stick in the mud, but the stratocharged saw's are real dog's at 9000'.

Andy