What size engines use air ,oil & water/antifreeze cooling? Why?

[Langanobob]

You also save some weight, a good thing when airborne

Also a good thing on a bike 

[vw151]

Ultimately, all motorcycle engines are "air-cooled" but reasonable people understand that the term "air-cooled" specifically refers to engines which shed heat without the assistance of a dedicated liquid circuit.  Is there a limit to engine size due to air-cooling?  Not at all.

OK, first, well put.  I think I had a good understanding of this to begin with but wanted to hear a more precise explanation.  This part of your response really hits the nail on the head.  There is no reason for anyone to bring up the point that all engines are "air cooled"  technically that is true but not the question at hand. 

Anyway.  From what I've read here is what I have gathered in simple terms

1. Air Cooled -  Just an engine, doing it's thing with oil as a lubrication but not channeled anywhere specific for cooling.  An oil cooler could  be used to cool the oil.  So, the oil cools the motor but isn't specifically routed through the motor to do so and otherwise like all engines the heat leaves the engine via the metal contacting the outside air. 

2.  Air/Oil cooled -  Just like air cooled except the oil also runs through channels much like a water cooled engine to more evenly cool the motor.  So, more oil is likely required since it will be running through channels and also doing it's normal lubrication job. 

side note- air cooling and air oil cooling will allow larger variances in temperature so the way the engine is designed will have to allow for this higher variance through lower tolerances and ultimately lower power in order to keep temps in check. (less fuel/air can be burned and less RPM can be achieved as both of these things make more heat)

3. Water cooling - separate fluid and channels dedicated to cooling the engine, a water pump moves the fluid through the engine and a dedicated radiator cools the fluid.  A thermostat regulates the temp of the coolant with the use of a fan on the radiator in many cases and the engine ultimately stays at a more even temperature and is also able to dissipate a larger amount of heat allowing for more power to be made with out overheating the engine via higher RPMs and larger air/fuel burned. 

[scott_araujo]

This is the lableling I've usually seen too but I think there is another option, call it 2 1/2.

Oil cooled with the oil being forced through channels similar to those used in water cooling.  It sounds like this is what the 900 does from what has been metioned here.  This is a step up from option 2 you mentioned where the oil being used as lubrcant is simply pushed through an external cooler, there are additional passages the oil is pumped through exclusively to remove heat from the engine.  Someone correct me if I'm wrong.

Scott

[vw151]

This is the lableling I've usually seen too but I think there is another option, call it 2 1/2.

Oil cooled with the oil being forced through channels similar to those used in water cooling.  It sounds like this is what the 900 does from what has been metioned here.  This is a step up from option 2 you mentioned where the oil being used as lubrcant is simply pushed through an external cooler, there are additional passages the oil is pumped through exclusively to remove heat from the engine.  Someone correct me if I'm wrong.

Scott

That is what I was meaning to say for option 2.  Oil cooler doesn't change the definition at all by what I'm reading here.  The difference between air cooled and oil cooled simply seems to be the pushing oil through cooling channels or other things specificly made for cooling. 

[DuciD03]

I was trying to get away from the "semantics" and precise definition and get further into the technical why and how it works; there has been some intresting explanation as to how and why; and perhaps part of the explanation is in the definition ... but the actual definition isn't as important as the other technical details ... some noted below.

- oil being circulated as a coolant jacket around the 900 cylinder (is that the only engine that does that?) and

water cooling with a thermostat will hold the temp at a better constant, holding a constant and more precise engine temp to design around ....

that water absorbs heat at twice the rate of oil ... (who knew?)

This has some real engine design considerations.  I have some understanding of how engines work and are cooled but have learnt some further details ...

... the internet can be the collective brain ... (lol. can it?)

[Keld]

Air-cooled 1200 hp diesel that runs in desert land: http://www.army-technology.com/projects/merkava/

[Cloner]

This problem is far too complicated to fully describe in this forum, but I'll throw a couple of more wrenches into the works.

As far as I know, all bevel driven Ducatis, both desmo and spring head, were air-cooled animals.  When the Pantah was introduced, they, too, were air-cooled.  The first liquid cooled Ducati I remember was the 851 in the late 80s.  All four valvers since (888, 916, 748, 996, 998, 749, 999, 848, 1098, 1198) have been liquid cooled.  All Pantah derivatives (400, 500, 600, 650, 696, 750, 800, 900, 1000, 1100) with the exception of the hybrid ST3 engine have been air cooled.  The ST3 engine was liquid cooled.

Air cooled engines have a problem disposing of heat near the centers of their cylinder heads, as all heat generated must be transferred toward the cooling surfaces via conduction.  This can lead to detonation problems and there is a practical bore limit given a valve/spark plug/compression/rpm ceiling/cylinder arrangement in four stroke gasoline engines.  Lower operational speeds give longer time intervals to dispose of heat.  Valves are cooling devices (heat sinks), but can also be hot spots for detonation.  Compression directly affects the predisposition of an engine to detonate.

Diesels are another matter entirely, as diesel is a VERY high octane fuel by comparison.

The assertion that more valves =  more air/fuel is a bit simplistic.  When it comes down to it, an engine is an air pump.  A 900cc air cooled engine moves as much air per stroke as a 900cc liquid cooled one, yet a liquid cooled engine will typically make more power than an air cooled one. The difference can be attributed to a few primary design differences. 

First, a liquid cooled engine, since it is more resistant to detonation, can be designed with a higher compression ratio, yielding greater volumetric efficiency at a given speed. 

Second, since they can move heat away from the cylinder and cylinder head more quickly, liquid cooled engines can operate at higher speeds, yielding more horsepower (as horsepower is a simple mathematical formula relating torque to rotational speed).  These higher operational speed mean the liquid cooled engine pumps more air/fuel (the same per rev, but more revs!).

Finally, since Ducati liquid cooled engines use three or four valves per cylinder,which flow more air/fuel over a given time interval than two valves, the cam profiles can be optimized to allow better cylinder filling and exhausting in a shorter portion of the piston's stroke.  This also yields greater efficiency and more power.

The emissions advantages of liquid cooling have already been mentioned, so I won't venture there.

It's been a little more than 20 years since engineering school, so forgive me if I don't remember all the math to support my assertions, but this is kinda how I remember engine design.  Remember that the best internal combustion engines run around 25% efficiency, and you'll see why even a small increase in efficiency is worth pursuing.

[DuciD03]

 
Dude!

Posted by: Cloner

This problem is far too complicated to fully describe in this forum, but I'll throw a couple of more wrenches into the works.

As far as I know, all bevel driven Ducatis, both desmo and spring head, were air-cooled animals.  When the Pantah was introduced, they, too, were air-cooled.  The first liquid cooled Ducati I remember was the 851 in the late 80s.  All four valvers since (888, 916, 748, 996, 998, 749, 999, 848, 1098, 1198) have been liquid cooled.  All Pantah derivatives (400, 500, 600, 650, 696, 750, 800, 900, 1000, 1100) with the exception of the hybrid ST3 engine have been air cooled.  The ST3 engine was liquid cooled.

Air cooled engines have a problem disposing of heat near the centers of their cylinder heads, as all heat generated must be transferred toward the cooling surfaces via conduction.  This can lead to detonation problems and there is a practical bore limit given a valve/spark plug/compression/rpm ceiling/cylinder arrangement in four stroke gasoline engines.  Lower operational speeds give longer time intervals to dispose of heat.  Valves are cooling devices (heat sinks), but can also be hot spots for detonation.  Compression directly affects the predisposition of an engine to detonate.

Diesels are another matter entirely, as diesel is a VERY high octane fuel by comparison.

The assertion that more valves =  more air/fuel is a bit simplistic.  When it comes down to it, an engine is an air pump.  A 900cc air cooled engine moves as much air per stroke as a 900cc liquid cooled one, yet a liquid cooled engine will typically make more power than an air cooled one. The difference can be attributed to a few primary design differences. 

First, a liquid cooled engine, since it is more resistant to detonation, can be designed with a higher compression ratio, yielding greater volumetric efficiency at a given speed. 

Second, since they can move heat away from the cylinder and cylinder head more quickly, liquid cooled engines can operate at higher speeds, yielding more horsepower (as horsepower is a simple mathematical formula relating torque to rotational speed).  These higher operational speed mean the liquid cooled engine pumps more air/fuel (the same per rev, but more revs!).

Finally, since Ducati liquid cooled engines use three or four valves per cylinder,which flow more air/fuel over a given time interval than two valves, the cam profiles can be optimized to allow better cylinder filling and exhausting in a shorter portion of the piston's stroke.  This also yields greater efficiency and more power.

The emissions advantages of liquid cooling have already been mentioned, so I won't venture there.

It's been a little more than 20 years since engineering school, so forgive me if I don't remember all the math to support my assertions, but this is kinda how I remember engine design.  Remember that the best internal combustion engines run around 25% efficiency, and you'll see why even a small increase in efficiency is worth pursuing.

standing

.... wow .... right on ... and that was the more technical design info I was searching for; thanks!

Ummmm ... It'll trake a few days to absorbe and ask an intelligent qestion back .... wow right on!  Dont have an engineering background; but! i do have a design and some mechanical know how ...

[moto]