Turbo intercoolers - purpose?

Long and boring, I'm afraid ;o)

I'm trying to understand the purpose of intercoolers on turbo-charged cars. I've done a web search and the basic reason to cool the intake charge seems to be to reduce the possibility of detonation. That seems quite logical, and I'm quite happy with that.

However a lot of the sites talked about reducing the "density" of the intake charge, (since cold air is denser than hot air), thereby increasing power - even the excellent howstuffworks website. I have a big problem with this. As I understand it, the statement that "cold air is denser than hot air" has to be qualified by adding "at the same pressure", and surely the pressure on the inlet side of the intercooler is different than the outlet.

I can understand how on a cold day, more molecules of air are drawn into the engine than on a hot day (because the air is denser), and the engine will have more power.

But I can't see how this argument can be extended to intercoolers. The same number of molecules leave the intercooler as entered it, and surely this depends on the density of the ambient air, not the density of the air leaving the intercooler?

To put it another way:

For the intercooler to increase the mass of air entering the engine, it must increase the mass flow upstream at the air inlet. I just can't see that happening, when you consider all the plumbing in the way (turbo, air mass meter, throttle plate, air filter, etc).

Can someone help!

Reply to
Kenny
Loading thread data ...

"Kenny" mumbled:

Yup, that's right, so you stuff more in the input and more come out the other end, but because they're more tightly packed they take up less space and the engine can cram more of 'em in. More air allows more fuel allows more power.

Reply to
Guy King

In message , Guy King writes

Exactly. If Kenny wants to learn some more he should do a search on Charles's Law. There are loads of sites but here's just one :-

formatting link

Reply to
Paul Giverin

Pressure drop across a decent intercooler is pretty low. As your limiting point is the engine not the turbo then for the same inlet pressure at the engine colder air will be denser & you can get away with higher inlet pressures before you suffer preignition. (Technically most of the ones you see are aftercoolers, intercoolers used to live between the twin turbos on loder big engine designs)

Reply to
Duncan Wood

Right, got it! I was overlooking the backpressure effect.

It comes from an argument at work - I was convinced that intercoolers of themselves didn't increase horsepower, but just allowed you to run more boost (a bit like water injection kits).

I owe him a fiver now :-(

Reply to
Kenny

Yep! Got it, thanks!

Reply to
Kenny

Grunff mumbled:

Which is why steam turbines at power stations have condensors on the output....huge pressure drop at the outlet means greater effective pressure across the turbine. You don't think they have those socking great cooling towers for nothing, do you!

If they didn't have 'em, they'd be venting half used steam to the atmosphere with all the attendant waste involved. As it is, they cool the steam, which "sucks" on the outlet of the turbine. The water used to cool the steam is then itself cooled by evaporation. The reason they don't cool the working steam directly is that it's returned to the boiler in a closed loop so that they don't have to keep demineralising more and more water.

Reply to
Guy King

Yeah, I *know* that - I thought it was implicit "I was convinced that intercoolers themselves didn't increase horsepower, but just allowed you turn the boost up, which obviously

*does* increase horsepower"

Putting a ladder next to a wall doesn't help you see over it. You have to climb it first!

Reply to
Kenny

When you say "AT THE AIR INTAKE", do you mean the intake to the intercooler, the turbo or the engine?

It does go up, yes. The reason is because colder air takes up less space so more can be pressed into a fixed volume.

Mark.

Reply to
<mj210168

mumbled:

No it won't. It'll have the same percentage of oxygen as the rest of the world.

It'll have more total oxygen, but only by virtue of there being more air, so it's misleading to say it has a higher /content/.

Reply to
Guy King

Ahem. Oxygen isn't fuel.

The 'oxygen content' remains the same; just that there's more available for combustion if a cylinder is being filled with denser air.

Reply to
Grimly Curmudgeon

We learn something new every day! I never did understand the point of cooling the outgoing steam.

The Dervboy

Reply to
DervBoy

Well unless it's a very hot turbo.....

Reply to
Duncan Wood

Duncan Wood mumbled:

That's getting heavier all the time!

Reply to
Guy King

I think you'll find that the oxygen *does* burn.

Mark.

Reply to
<mj210168

I'm not sure about that, don't you need fuel as well?

Reply to
Tim S Kemp

What exactly do you mean?

Fill a chamber with hydrogen, and yes, an oxygen jet will burn. But by no conventional definition can they both be saif to be 'fuels' - in the hydrogen chamber example, the oxygen is the fuel.

In general, the petrol/hydrogen/propane/whatever is defined as the fuel, and the oxygen in the air as the oxidiser.

Reply to
Grunff

So are you saying that oxygen reacts with oxygen to produce a significant rise in temperature?

Shaun

Reply to
Shaun

The petrol will not burn without the oxygen and the oxygen won't burn without the petrol (or some other additive), the combination of the two are the fuel, each on their own are not much use to an engine.

To be honest, I'm not sure if you can count the petrol as a fuel and the oxygen as a fuel, or if they are only classed as fuel once combined...

Mark.

Reply to
<mj210168

mumbled:

Oxygen doesn't burn...fuels burn /in/ oxygen, combining with it to release energy.

No, you can't. Oxygen is the oxidiser and petrol is the fuel. Combined they make a fuel/oxidiser mixture.

You weren't really awake during your chemistry lessons, were you!

Reply to
Guy King

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.