h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I have a bvery vague idea but I don;t actually know what an intercooler does, nor how it does it.
I believe it is all down to cooling the mixture in the turbo so that it is more dense thus providing more fuel/air mixture to the engine. But whether that is correct or not, and how it actually cools the mixture, I know not.
anyone explain it for me?

As far as I remember an intercooler sits in between the turbo and the engine inlet valves - the turbo is compressing the mixture, which of course heats it up, by passing the mixture through what is in effect a radiator (the intercooler) it cools everything down - thus increasing the density of the mixture meaning you get more the fuel/air mixture into the cylinders at each cycle.

Cheers Whisky, that makes sense of what little I knew.

*goes into shed to find old radiator and strap it onto his car*

Whisky,

That's pretty much exactly right. It can make a big difference to the efficiency of a turbocharged engine and is a useful accessory. They can be quite bulky however so are usually only found on larger engines.

Engine efficiency depends on the difference in temperature between the air entering and the exhaust gasses leaving the cylinder (amongst other things) so cooling the ingested air or air/fuel mixture is beneficial. The turbine gets very hot from the exhaust gasses as well as during the process of compressing the air so tends to deliver very hot air to the engine.

I imagine it would be possible to have one fitted to most turbocharged engines by a tuning specialist.

F

The power of an internal combustion engine is directly proportional to the mass of air taken as per the perfect gas equation.

pV = mRT

where p=pressure, V=volume, m=mass, R=constant for the gas and T=temperature

Therefore m = pV / RT

Hence if you reduce T in an intercooler you get more mass and more power
QED

Travel hopefully...

How does cooling the air increase its mass?

I recognise the equation but if the turbine moves a certain mass of air per second into the engine, cooling that air after it has passed the turbine will not make more of it. It will, I suppose, decrease the manifold pressure which might allow the turbine compressor to pump more air.

Anybody have the answer to this?

Clearly there is more to this than I thought.

F

To all intents internal combustion engines run on fresh air. The fuel only starts the reaction. For any given turbine speed the output volume from the compressor will be constant. Remembering the Perfect Gas Equation, by reducing the temparture, in the intercooler, the mass of air available for combustion increases. Hence you get more reaction for the same ammount of fuel. More bang for your buck...

WanderingAlbatross,

"For any given turbine speed the output volume from the compressor will be constant."

Right. Let's say the turbine is providing a constant 50 litres of hot air per second. We introduce the intercooler and cool the air.

PV = nRT

reducing T is balanced by either:
P/ressure reduces
V/olume reduces
n/umber of molecules (mass) increases
R? I don't think this constant should change.


If the pressure is reduced the turbine can pump more air so the throughput will rise.
If the volume is reduced presumably the walls of the container must move inwards - not a likely scenario.
If the mass increases the question arises as to where the additional mass came from.

The conclusion is that cooling the turbine output reduces its pressure and allows the turbine to pump more air. The assumed 50 litres per second should rise as the temperature and pressure fall. The aspirated air density rises feeding more air per second to the engine - as you suggested earlier.

Makes sense I suppose.

F

so basically it is a temperature driven compressor bolted onto the inlet manifold then?

Like the ram-air stuff on motorbikes and high performance cars where they use the forward motion of the car and an airscoop to provide chilled condensed air to the engine?

Presumably one could use it without a turbo, but it is more effective with a turbo since the exiting gasses from a turbo are so much hotter?

The turbocharger is a compressor driven by a gas turbine in turn driven by the exhaust gasses. The intercooler fits between the compressor discharge and the engine inlet manaifold. The intercooler cools the air after it has been compressed and before it enters the engine...

well yes I understand that (as should we all after the explanations above!), but by the act of cooling the gasses it increases the density thus compressing it, at least that what I understand from the above equations.

The likening to motorcycle / performance (ie race) cars was that I know for a fact that on at least one motorbike there is a ram air scoop at the front which runs through a system to cool the air down so that you get more incoming air. This is particularly important at speed since it helps ensure there is enough fuel air going into the engine at high revs/speed to ensure it runs properly.

Now if all an intercooler does is cool things down a bit (thereby increasing density) then they two things sound very familiar do they not?

We are talking perfect gasses and theory and things do get a lot more complicated but lets look at the combined gas equation that states:-

P1 V1 / T1 = P2 V2 / T2

This means that when you compress a gas it gets hotter. However heat equals energy and more energy means the molecules within the gas will be further apart hence less mass.

When the intercooler cools the compressed gas it takes away some energy (heat) hence the molecules are closer together. Mass increases so there is more raw material to react....

Ah well, I guess I shall leave off the practical comparison of engine components then i don;t have a problem with the theoretical gasses stuf so far posted, and wasn;t questioning that.