why dont 2 strokes use thermostats?

[Bobt250]

What I was trying to say, and not very well was this:

Imagine that the water moving in the water jacket of the cylinder was broken down into units, lets say CC's. As a given unit of water passed over a given point of the hot aluminum it would absorb some heat. The fact that it is moving faster means that a given unit of water absorbs less heat BUT, there is another unit of cold water following right behind and will pick up it's share of heat. Each individual unit of water picks up less heat but there will be more units of water picking up heat in a given period of time. The total amount of heat removed should be more since the water isn't held in place by a thermostat resulting in colder water and the difference in temperature is greater between the aluminum and the water.

Oh well. I think, so therefore I am.

Huh?

 

[DVO]

10 dudes (think of them as the surface area inside a water jacket) work on an assembly line. They fill boxes(think of them as cc's) on a convetor belt. They put a little piece of "heat" (think of them as heat.:D) into each box as it goes by. The belt moves constantly at a slow speed and by the time the boxes exit the factory they are full. The boxes then go to the loading dock(radiator) where they are emptied by 30 dudes (you can fit a lot more "dudes" in a radiator). The boxes stay on the belt and carry on back inside to be refilled. This continues in one big loop.
Someone in the head office wants to increase productivity and speeds up the belt. If the dudes inside are not already working at full capacity (transferring maximum heat) this will work--more boxes going by faster=more heat going outside. If the belt speed is too fast, the amount of heat put in each cc will be limited by the number of dudes transfering heat. Even if the cc's go out only partially full, they will take out more heat than if they were at the slower speed and full.
This seems just too simple to me. If I'm wrong, explain why. Make it just as simple please.

 

[Bobt250]

Hey Dude,

I love your Dudes explanation. I wonder if the other Dudes around here like your Dudes too?

Serioulsy, I really like that example. I agree, it seems simple to me too.

From one Dude to another Dude,

Chill out

 

[jmics19067]

love the dudes but that only explains the water pump and water thru the jacket speeds . But what happens when the fatory behind the dudes speed up pruduction and make more heat? Do they go on strike until you hire more dudes? or ask for a raise?

 

[Bobt250]

The temperature will increase, That is the problem with no thermostat. Temperature is not constant but I believe overall lower. Personally I'm not defending the lack of thermostat. I like a constant operating temperature. It was me who talked my buddy into putting an aftermarket thermostat on his '85 YZ250. Two of them wouldn't fit on my CR, he needed only one.

 

[DVO]

jmics19067: When they speed up production they speed up the conveyor belt!
I assume that all the manufacturers design their systems to cool under the worst conditions and the piston clearance is designed to be optimum when the motor gets hottest. I'm no mechanic but I think the water pump is"direct drive"(someone correct me if I'm wrong) and the speed is directly related to engine speed. If indeed this is the case, then when the engine is producing the most heat, the pump is producing the most flow and therefore the cooling power of the system is increased. If you don't have a well regulated cooling system to keep the motor at optimum temperature, then clearances do not remain constant and unnecessary wear is taking place.
I don't know how many bikes out there use thermostats, but I'd be interested in knowing what temp they regulate at. Anybody got any info? I think I'll put one on mine. Right now I've got a cardboard cutout behind my left rad:also inconsistent. Later dudes...

 

[NVR FNSH]

Something about heat xfer class and MdotCpdT comes to mind. Mdot is mass flow as in lb/sec, Cp is specific heat and dependant upon the fluid AND temp, dT is temperature differential. The jist of it is that by changing the fluid velocity - water or air - you are changing the heat xfer capabilty. Somewhere in there you also have a heat balance equation or something - goes into = goes outa.

Brian

 

[danny66]

huh uh

Do not make the mistake of comparing liquids to gases. you can not pressurize a liquid. A gas, yes, very compressible. This is why an airfoil works so well in a liquid, because a liquid cannot be compressed. If anyone wishes to dispute this feel free to post.

 

[TexKDX]

Re: huh uh

Originally posted by danny66
Do not make the mistake of comparing liquids to gases. you can not pressurize a liquid. A gas, yes, very compressible. This is why an airfoil works so well in a liquid, because a liquid cannot be compressed. If anyone wishes to dispute this feel free to post.

Think again, Danny. Liquid can be compressed; just not nearly as much as a gas can, and it takes much more pressure to get it to compress. It will also generate alot of heat in the process.

Relevant to the topic being discussed? Not really.

 

[danny66]

wasn't replying to these

My post was a reply to something i was reading on the second page of this thread.
and average people do not have the means to compress a liquid. If you are thinking of an example, please share.

 

[demographic]

"Er what was the question? Oh yes Black holes and event horizons and infinate density?" "No it was about two strokes and thermostats!" Lost the plot there a bit dont you think?

 

[Buckholz]

Entertained by yawls discussion. First, my last four dirtbikes have had thermostats. Thats 3 KTM 380s and one XR650R. The XR's thermostats are defective from the factory and fail half open. No thermostat problems in the three KTM's. My two stroke snowmobile also has a thermostat.

My background is as a MechEng with specialty in thermal science. My learnings, feelings ,reading, and experience had led me to believe that less restrictions and more flow is always better. Lots of arguments with buddies,....


Wrote Kevin Cameron (of Cycle World Tech fame) and he confirmed that more flow always transfers heat better.... except in one case. That is if flow rates lead to cavitaion where the coolant "pulls away" from the tubes and or the impeller ends up cavitating (read about in submarines books) and reducing flow.


BTW, the right KTM radiator is thermostatically controlled. In my owners kit from KTM, a goofey black plastic piece was included. It exactly matches the left radiator so one can use it for completely blocking off flow.

And yes, at 7,000' elevation, there are times when we need to block flow in high speed operation.

And my KTM380 will sit on the sidestand and idle for 10 mins during warmup.

 

[demographic]

Buckholz
On my Kx 500 the cylinder head has only one water pipe leading to the left radiator then the water goes across to the right rad then down to the water pump. Is your KTM the same apart from a thermostat between the two rads? If so, do you know how long it is? I have been looking into fitting an in line thermostat to my bike as it is geared up for road use and gets a lot of air through the radiators and also if it helps warmup then next door don't have to listen to it for as long:o. I have been following this discussion for a while and waiting for some usefull information( usefull to me anyway) to pop up. Any information that you can give me would be apreciated. Cheers:)

 

[Buckholz]

Hey Demo, I raced a KX500 before I turned orange. I'll look at my ktm tonight and a KX500 tomorrow and see if I have any ideas on plumbing.....

 

[demographic]

Thanks very much thats the best news I have heard all week.Cheers:)