Engine overheating - greenhouses - and the 2nd Law of Thermo

[kerplunk]

Got a wierd thermodynamics issue that I'm hoping to get some help with.

A friend with a heavily souped up old air-cooled Kawasaki living in Sweden had never experienced engine overheating problems before as he roared around the chilly north. However he recently got a new long term job in Dubai and decided to ship his beloved kwak over for the occasional thrash around the desert but now - oh no! - he's experiencing engine overheating problems.

He's using exactly the same fuel and a mechanic has checked everything else is tickety-boo and suggested it's simply the higher air temperatures in Dubai causing the problems with his heavily souped-up engine which my friend has accepted as the reason.

However I've told him the mechanic is talking junkscience because the 2nd Law of Thermodynamics states a cooler body cannot increase the temperature of a warmer body (without some kind of 'pump' doing work) so it can't possibly be the higher air temperature in Dubai causing the overheating problem as the 'warm' air is still a darn sight cooler than the temperature of the engine (and I don't see a 'pump' to transfer energy from the cooler air).

So how can the mechanic possibly be right?

(I've also told my friend the earth's alleged 'greenhouse effect' is a load of bks for exactly the same reason)

[98elise]

The rate of removing heat from the engine is directly related to the temperature difference between the engine and the air (delta T).

The hotter the air, the less it it is able to cool the engine.

If the engine has been modified then its an even bigger issue as its generating more heat than the cooling system was designed for in the first place.

[kerplunk]

98elise said:

The rate of removing heat from the engine is directly related to the temperature difference between the engine and the air (delta T).

The hotter the air, the less it it is able to cool the engine.

If the engine has been modified then its an even bigger issue as its generating more heat than the cooling system was designed for in the first place.

But how can the engine temperature increase - surely that breaks the 2nd Law?

[don4l]

kerplunk said:

However I've told him the mechanic is talking junkscience because the 2nd Law of Thermodynamics states a cooler body cannot increase the temperature of a warmer body (without some kind of 'pump' doing work) so it can't possibly be the higher air temperature in Dubai causing the overheating problem as the 'warm' air is still a darn sight cooler than the temperature of the engine (and I don't see a 'pump' to transfer energy from the cooler air).

So how can the mechanic possibly be right?

Are you saying that engine ends up hotter than the combustion temperature?


If not, then the "cooler" air is not heating up the engine. It just isn't cooling it as quick.


0/10 for useless trolling.


Don
--

[bitwrx]

You're putting the same amount of energy in (burned fuel) , but taking less out. How can the temp *not* increase?

[98elise]

kerplunk said:

98elise said:

The rate of removing heat from the engine is directly related to the temperature difference between the engine and the air (delta T).

The hotter the air, the less it it is able to cool the engine.

If the engine has been modified then its an even bigger issue as its generating more heat than the cooling system was designed for in the first place.

But how can the engine temperature increase - surely that breaks the 2nd Law?

The combustion is adding energy, and the cooling system is removing it.

The cooling systems ability to remove energy has been altered by the hotter air temperature. The hotter the air temperature, the less energy it can remove. Add it the fact that the engine is producing more power than the cooling was designed for anyway, and you have an overheating issue.

[kerplunk]

don4l said:

Are you saying that engine ends up hotter than the combustion temperature?


If not, then the "cooler" air is not heating up the engine. It just isn't cooling it as quick.


0/10 for useless trolling.


Don
--

No I think the engine is getting hotter as a whole but it's the surface of the engine that's 'meeting' the air.

The temperature of the air is the only thing that's changed but it's still at a lower temperature than the engine surface so can't cause the temp to rise due to the 2nd Law.

Simples!

[kerplunk]

bitwrx said:

You're putting the same amount of energy in (burned fuel) , but taking less out. How can the temp *not* increase?

Ahh so you're saying the presence of an 'energy source' is a factor then?

[kerplunk]

98elise said:

The combustion is adding energy, and the cooling system is removing it.

The cooling systems ability to remove energy has been altered by the hotter air temperature. The hotter the air temperature, the less energy it can remove. Add it the fact that the engine is producing more power than the cooling was designed for anyway, and you have an overheating issue.

Yes I think I'm getting it now - it's the presence of an ENERGY SOURCE that means there's no breaking of the 2nd law.

I guess that means the greenhouse effect doesn't break the 2nd law either due to the presence of the sun?

Damn!

[98elise]

kerplunk said:

bitwrx said:

You're putting the same amount of energy in (burned fuel) , but taking less out. How can the temp *not* increase?

Ahh so you're saying the presence of an 'energy source' is a factor then?

Of course. The issue isn't that the air is increasing the temperate, its that its no longer taking as much out.

The source of the heat is the fuel.

[kerplunk]

Thanks elise-man.

I guess I ought to come clean now - there is no friend in Dubai, or Sweden (but I do own a 'souped up' ol air-cooled Kawasaki and have had overheating problems on hot summer days).

The real reason for the post was an 'interesting' discussion about the 2nd Law in relation to the greenhouse effect in the climate change thread with turbobloke