Why is it so?

[Blr243]

Our cars and motorbikes have either radiators or oil coolers, My 185 Honda bike is cooled only by the air hitting the fins as I move forward ...our little gen sets sit still often with no wind and bugger all venting but they don’t overheat and blow up ....I must add that on a hot day, or really any day I would help my generator by ensuring it’s in the shade

[trekin]

If you are wanting to know why a stationary small engine dosen't over heat because it is not moving though the air, well it is because they are fitted with a blower fan on their flywheel, and cowlings to direct the air over the cooling fins. Simples really.

[Blr243]

Just like an internal fan on a pc. Bugger me. Now I know why it is so !

[Oldbloke]

Just like an internal fan on a pc. Bugger me. Now I know why it is so !

Lol. Like a lawn mower.

[eddievic]

That is not right in many cases... think like small engine chain saw or petrol washer engine or even a motorbike engine most do not have fans on their cranks (well the smaller ones anyway)

These engines are quite small and just fins around the cylinder are enough for the heat to radiate to the atmosphere. (The 25cc engine in many chainsaw or whipper snippers is around 25ml... so you can fill 40 of these engines with 1 litre milk bottle) they just don't generate huge amounts of heat that would melt metal. Plus 2 stroke oil helps cool the temps by retarding the burning/flame.

The bigger the engine the more heat it will start to generate (remember heat and power are generated from the burning of fuel). Heat is also generated by friction. So more moving parts more is the need to dissapate heat.

Now going back to your bike, generally you do not sit there and rev the s**t out of it (and if you did, eventually you would throw a rod).. and those times that you are reving the bejesus you are probably driving at 40 or 60kph or more. There is enough air flow over the engine to help it keep cool.
And yes the fins help by giving it more surface area to dissipate from.

(For bonus extra points) At lower speeds like idle the engine does not produce enough heat.

[trekin]

That is not right in many cases... think like small engine chain saw or petrol washer engine or even a motorbike engine most do not have fans on their cranks (well the smaller ones anyway)

These engines are quite small and just fins around the cylinder are enough for the heat to radiate to the atmosphere. (The 25cc engine in many chainsaw or whipper snippers is around 25ml... so you can fill 40 of these engines with 1 litre milk bottle) they just don't generate huge amounts of heat that would melt metal. Plus 2 stroke oil helps cool the temps by retarding the burning/flame.

The bigger the engine the more heat it will start to generate (remember heat and power are generated from the burning of fuel). Heat is also generated by friction. So more moving parts more is the need to dissapate heat.

Now going back to your bike, generally you do not sit there and rev the s**t out of it (and if you did, eventually you would throw a rod).. and those times that you are reving the bejesus you are probably driving at 40 or 60kph or more. There is enough air flow over the engine to help it keep cool.
And yes the fins help by giving it more surface area to dissipate from.

(For bonus extra points) At lower speeds like idle the engine does not produce enough heat.

Don't know what small engine chain saw or petrol washer engine, or whipper snipers etc you use, but I've never seen one without a blower fan (the fins on the flywheel) fitted.

[Oldbloke]

Yep, fins/fan on fly wheel.

[eddievic]

Hmm. Go figure i learnt something new.

Had a look at two petrol pressure washers i had. And i can see the cooling fins on the flywheel side of the engine. I am thinking you mean the blower fan is built into the fly wheel (inside the casing).

I know on a rideon the fan is outside clearly visible. Never thought it would be inside the engine casing.

[trekin]

Hmm. Go figure i learnt something new.

Had a look at two petrol pressure washers i had. And i can see the cooling fins on the flywheel side of the engine. I am thinking you mean the blower fan is built into the fly wheel (inside the casing).

I know on a rideon the fan is outside clearly visible. Never thought it would be inside the engine casing.

Yeah mate, the fan is built into/onto the flywheel, the "fins" you see are the fan blades. And only some rideons have seperate cooling fans, usually the larger 2 cyclinder John Deer etc. In Amercia they call these yard/garden tractors as opposed to rideon's.

[Oldbloke]

This is typical.

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[deye243]

That is not right in many cases... think like small engine chain saw or petrol washer engine or even a motorbike engine most do not have fans on their cranks (well the smaller ones anyway)

These engines are quite small and just fins around the cylinder are enough for the heat to radiate to the atmosphere. (The 25cc engine in many chainsaw or whipper snippers is around 25ml... so you can fill 40 of these engines with 1 litre milk bottle) they just don't generate huge amounts of heat that would melt metal. Plus 2 stroke oil helps cool the temps by retarding the burning/flame.

The bigger the engine the more heat it will start to generate (remember heat and power are generated from the burning of fuel). Heat is also generated by friction. So more moving parts more is the need to dissapate heat.

Now going back to your bike, generally you do not sit there and rev the s**t out of it (and if you did, eventually you would throw a rod).. and those times that you are reving the bejesus you are probably driving at 40 or 60kph or more. There is enough air flow over the engine to help it keep cool.
And yes the fins help by giving it more surface area to dissipate from.

(For bonus extra points) At lower speeds like idle the engine does not produce enough heat.

You left out one very important heat generator ...... compression

[Larry]

Most of the small motors that you talk about that dont have fans are all 2 stroke. Without doing any google I think the reason these can run without fans is that the compression is very low and hence not as much heat is generated on containg an explosion,

[deye243]

Most of the small motors that you talk about that dont have fans are all 2 stroke. Without doing any google I think the reason these can run without fans is that the compression is very low and hence not as much heat is generated on containg an explosion,

Not my two chain saws they both have good compression heaps of torque ......

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[Blr243]

One October I borrowed a quad from a grazier when I was hunting cape York ...he told me during the hottest part of the day that I should run it thru the edge of a swamp occasionally to get some splash on it to help it from overheating ....he said that originally there was an oil cooler on the front of it but one day bull catching a bull ripped the oil cooler of the front with his horns .....this is Not ideal but still better than having a bull rip you of the front of the quad With its horns .....maybe the bull was cranky because he was overheating during the chase ......maybe scrub bulls need internal fans

[Larry]

@dye243 yes but they both have fans.

[trekin]

@dye243 yes but they both have fans.

So what 2 stoke stationairy engines are you talking about. Not saying they're not out there, but for the life of me, can't think of one.

[Larry]

I have 2 whiper snipers niether of them have any fans on them. the crankcase is sealed by the fuel tank.

[Oldbloke]

OK. I just googled sthil fly wheel chainsaw and whipper snipper. These are the results.

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They both have fans. Unless the cooling fins are huge they have to have them. And don't forget 2 strokes fire twice as often as a 4 stroke. Motor bikes are an exception because you are moving.

[eddievic]

But if that fan is enclosed in a fully sealed casing, OB?

After that message i went and had a look at my two petrol pressure washers... but are fully sealed

[deye243]

I have 2 whiper snipers niether of them have any fans on them. the crankcase is sealed by the fuel tank.

What brand and model I will bet there is a fan on both

[Die Judicii]

This is typical.

51YMc7Kk-IL._AC_SY400_.jpg

YEAH,,,,,,,, I see the fins,,,, but cos they look so clean and nice,,,, I'm guessing you've already scaled and gutted the fish.
Was it an Old Man Snapper ?

Pardon my weird sense of humor,

[Oldbloke]

But if that fan is enclosed in a fully sealed casing, OB?

After that message i went and had a look at my two petrol pressure washers... but are fully sealed

Must be air in and air out.......some how. Air must flow over fins at some point. Apparently it isn't obvious in your case.

BUT if a heat engine (in this case petrol) is operating it MUST somehow dissipate that heat or seize up.

I use the term heat engine because that is what it is... it works by the generation of heat when combustion happens. There are other heat engines. e.i. jets, steam, rotary, nuclear, I'm sure a few others.

Perhaps it rely's on water cooling?? Like an outboard motor.

[Die Judicii]

I use the term heat engine because that is what it is... it works by the generation of heat when combustion happens. There are other heat engines. e.i. jets, steam, rotary, nuclear, I'm sure a few others..

I'm no mechanic,,, but, exactly the same, only different I believe.

Heat is a by product that needs to be removed, for obvious reasons, as a result of and, after combustion which is brought about as a result of the "spark" which is introduced via timing, blah blah,, from the spark plug. (petrol/kero/gas engines)

The true ?? definition of the loose term of "heat engine" is more or less applicable to a diesel engine which gets its combustion due entirely to compression first and foremost,,, aided by (sometimes glow plugs) initially,,,, and the fine spray of fuel/air, mix, which then ignites without the introduction of a spark provided by a spark plug.

Either way,, the generated resultant heat is a by product that needs to be removed/controlled/dissipated by whatever means works best per individual case.

[Die Judicii]

And,,,,,,,, for those that have never seen/worked on/ or know about what is known as a "hot bulb motor" (usually single cylinder) motors.

Google, or go to a vintage/steam engine display and ask questions and look.
There is usually 2 or 3 working ones at least on display.
They commonly use sump oil as fuel, and were popular engines for driving pumps and extracting water from rivers/streams etc.

[Oldbloke]

https://en.wikipedia.org/wiki/Heat_engine

From Wikipedia, the free encyclopedia

In thermodynamics and engineering, a heat engine is a system that converts heat or thermal energy to mechanical energy, which can then be used to do mechanical work.

In any case it gets hot and if it aint cooled it will eventually stop.

My bet is on water cooling

Above is pretty much my understanding, well, It was when I went to trade school. A Loooong time ago. LOL

[boingk]

Fan forced, or simply made to run in a stationary passive cooled environment by sheer inefficiency of operation - ie rich mixture and retarded hehe) timing.

You will almost always have a fan, even if small, drawing air from the pullstart area, flywheel, or inside the case through a vented position suh as the air filter box etc.

- boingk

[Tiger650]

Finned cylinders / cylinder heads are heatsinks offering much greater surface area for waste heat to be drawn away by ambient temperature air, if essentially stationary such as a chainsaw or lawnmower etc there will be a ducted fan.
The 185 Honda is presumed mobile at whatever engine load but the engine manufacturer rightly assumes that higher engine loads will result in higher vehicle speed with subsequent higher airflow over the cooling fins and hence greater heat rejection to atmosphere.
Notice that the cooling fins are not aligned with anticipated airflow, this is to avoid laminar airflow across the fins which would impede heat rejection, turbulent flow is best.
Liquid cooling is more efficient in that engine operating temperature can be governed by a simple thermostat, on cold start coolant flow is almost nil but as coolant temperature increases the thermostat allows greater coolant flow through a heat exchanger and excess heat is dissipated to whatever secondary coolant is employed.
To the best of my knowledge there has never been a motor vehicle built with a "radiator".
Radiators are generally an [extremely inefficient] electric resistance element backed by a curved polished stainless reflector heater ?
The engine cooling system on most vehicles is a liquid to air heat exchanger, this providing a very large surface area to allow waste engine heat to be dispersed to atmosphere.
Marine diesels use the above principle to transfer unusable engine heat to seawater, most larger fixed fire protection pumps use a heat exchanger whereby some pump discharge water is passed by an engine coolant tube bundle containing primary coolant, heat transfer occurs and all is good
Engine oil is also a coolant and the above applies equally.

[TassieTiger]

^ has me baffled why the crab fishing boats that ice up so bad they look like huge bergs - don’t radiate their heat or pipe their exhausts via railings and similar to keep the ice at bay...it can take workers days and days to smash ice from their boat.

[Blr243]

TT. a how did you end up heating your bush hut?

[TassieTiger]

TT. a how did you end up heating your bush hut?

I am currently trialling 3;
1 - a small camp wood heater (issue is concern over co2 and not easy to regulate, due to small size, won’t last overnight).
2 - diesel heat exchange. Works well, but have to supply fuel and is a little noisy - humming fan.
3 - 200w solar panel, 520ah battery - inverted power to 1800w elec heater (7.5 amp draw per hour). Might be best option...but a bit of set up with vandal proof batt box).