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Why? (562 question)

Started by weimedog, January 04, 2016, 03:29:12 PM

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weimedog

Why did Husqvarna go to so much trouble to get those transfer ports close to the exhaust? And the heat from the exhaust in that section of the motor? Or am I misinterpreting what I see? Could be for space saving or something. But those transfer are routed right under and around the exhaust .. has to be that way to pick up heat. Does heating the charge from the exhaust pick up energy and add to total energy output?? Mechanically thats what a turbo charger does. An energy pump effectively. Takes heat/energy from the exhaust and turns it to first mechanical then pressure to force more energy back into the combustion cycle. A thermodynamic thing. Is this another thermodynamic game? Or is this strictly about emissions? Its backwards from the things I've seen with intercoolers and the like trying to cool therefor get a more dense charge... looking for a thermodynamic explanation. These saws obviously run well and are strong. The heat management thing is an issue I believe. Just really interesting and now I'm curious. And Husqvarna always has a reason....and the new Stihl's seem to have a similar layout....
Husqvarna 365sp/372xpw Blend, Jonsered 2171 51.4mm XPW build,562xp HTSS, 560 HTSS, 272XP, 61/272XP, 555, 257, 242, 238, Homelite S-XL 925, XP-1020A, Super XL (Dad's saw); Jonsered 2094, Three 920's, CS-2172, Solo 603; 3 Huztl MS660's (2 54mm and 1 56mm)

49er

Those transfer ports are long, to promote torque, and some heat will keep fuel from settling out of suspension.
Heck, I don't know but it sounds good. ::)
The 576 is the same design,NO?
Husqvarna EC390 365xt
Jonsered 2188 2165 2260 2253 70e
Redmax GZ4000

starmac

My money is on emission regulations.
Old LT40HD, old log truck, old MM forklift, and several huskies.

bacon

That's not really what a turbo does at all...heat is the enemy of forced induction as heat decreases air density and oxygen content. Preheating the mixture will decrease power, hence the introduction of intercoolers.

As pointed out already, it likely had to do with torque or hp curves at certain throttle positions. With 2-strokes, pressure is vital on intake and exhaust. Besides, the time the fuel/air charge spends in that port while making its way to the chamber is negligible. Just like with a radiator/intercooler, it takes some time to change the temp of the fluid.

Did you have a problem with the saw, it is it just something geometric that you noticed?

weimedog

Quote from: bacon on January 04, 2016, 10:02:43 PM
That's not really what a turbo does at all...heat is the enemy of forced induction as heat decreases air density and oxygen content. Preheating the mixture will decrease power, hence the introduction of intercoolers.

As pointed out already, it likely had to do with torque or hp curves at certain throttle positions. With 2-strokes, pressure is vital on intake and exhaust. Besides, the time the fuel/air charge spends in that port while making its way to the chamber is negligible. Just like with a radiator/intercooler, it takes some time to change the temp of the fluid.

Did you have a problem with the saw, it is it just something geometric that you noticed?

Actually that was my point that typically in any kind of forced induction heat has been considered the enemy. Intercoolers an enhancement designed to increase the density. Also on things like bearing life and the impact on the oil used to cool and lubricate bearings. I remember the big deal with water cooled turbo's on the Chrysler 2.2 turbo's. But ultimately its about converting as much "heat" into rotational energy as possible, and on the big picture the entire two stroke system is about the conversion of heat to rotation. So every bit of heat that leaves the system is energy that can't be converted to rotational energy. Turbo's are all about taking "energy" from the exhaust and turning it into a useful thing vs. waste via. driving a compressor to get more air into the equation therefore more potential power. Hence the thermodynamic reference. Where we the pure mechanical types get confused is heat is also the enemy of all things mechanical from charge density, bearings & oil, to expansion and contraction therefore tolerances. So the answer is to rid the system of heat tactically to enhance certain properties and the equation is about the mechanical properties enhanced are a greater net "positive" impact on the overall power output and reliability than the "heat" or energy lost at those locations.

So here is the 562 and a two stroke is in fact forced induction. Just instead of an exhaust driven turbo or a mechanically driven blower or supercharger, its using the piston & differential case pressure. So my question is why this new design where heat is obviously introduced into the charge? The  length and geometry of those transfers could have been in a lot of places. Even "cooled" closer to the intake side or where they usually are but they instead choose to route them under and around the exhaust where depending on whether your an optimist or a pessimist they either pick up heat or cool the exhaust...:) and its an obvious design choice relative to the heat especially when you look at the muffler design. I just am curious why? Does the expansion due to heat at that location change the fill speed? Maybe fill efficiency? Does more heat change the combustion efficiency? There has to be a reason. Also a demonstration of how its hard to out engineer the engineers if we don't understand the system, and I frankly don't...

One thing I do know is increasing compression is about using heat in a positive way to increase combustion efficiency. I wonder if this design is dong similar things in a way we just aren't used to seeing...:)

An article discussing turbo charging in a way we usually relate to:
http://www.forcedinductions.com/helpadvanced.htm

An interesting article discussing a nuance for those who want to immerse into the math .. discusses the Non adiabatic part of the system .. Maybe a clue. :)
http://www.hindawi.com/journals/ijrm/2012/625453/
Husqvarna 365sp/372xpw Blend, Jonsered 2171 51.4mm XPW build,562xp HTSS, 560 HTSS, 272XP, 61/272XP, 555, 257, 242, 238, Homelite S-XL 925, XP-1020A, Super XL (Dad's saw); Jonsered 2094, Three 920's, CS-2172, Solo 603; 3 Huztl MS660's (2 54mm and 1 56mm)

bacon

It's also possible that it is an efficiency thing.  If the fuel charge is warmer i will cool the cylinder less.  If the pre-ignition temps are higher, you have less thermal loss and more power (percentage-wise) going to the bar. 

Spruce_Goose

I've yet to see those cylinders in person... but we're talking stratocharged here right? Wouldn't that probably play a significant role? The 'fresh' air charge, I would guess, would spend more time next to the exhaust then the fuel/air mix coming up from the case, perhaps there is a reason there? Perhaps heating that fresh air simply helps the scavenging process and cools the exhaust simultaneously?

Or perhaps it has nothing to do with heat and they are where they are so that the incoming fresh air charge can enter through the piston and have a nice long area to 'hang out' in?


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