Well well, increasing the density may be a side effect of an intyercooler, but lowering the temperature is the prime objective to avoid pre-ignition.
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It would make no sense to compress (hence heat) the air and then cool the air (to "'reduce its density") and thereby decrease the pressure again. As Mike suggested in his initial post on the subject, if that's what one was doing, one might as well just compress (hence heat) the air less in the first place.
Furthermore, if, as in my cycle-by-cycle example, one cooled it without allowing the volume to change, the density would not change, but, rather, the pressure would fall. As I said, I don't know how these intercoolers work - i.e. whether they do their cooling under conditions which are closer to 'constant volume' or closer to 'constant pressure' (or somewhere in between).
In passing, I've found a quote in a Wikipedia article on adiabatic processes which supports my view (to which you responded "No, it's not that") as to why one needs the intercooler. Having gone through calculations relating to adiabatic compression in a petrol engine, it says ...
Wikipedia said:
Kind Regards, John
Ok, some of each but I don't know which comes first.
What about cars that have turbos without intercoolers?
https://en.wikipedia.org/wiki/Intercooler
http://www.turbosmart.com.au/technical-articles/how-an-intercooler-works/
What about cars that have turbos without intercoolers?
https://en.wikipedia.org/wiki/Intercooler
http://www.turbosmart.com.au/technical-articles/how-an-intercooler-works/
Presumably the turbos must be designed such that they do not compress to the extent that the resultant temperature rise is high enough to present a significant risk of premature ignition.
Kind Regards, John
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Overall, a Turbo is a device that uses what is otherwise a wasted thermal energy that is made to escape after mechanical energy has been extracted from a power stroke, this wasted energy flows out through an exhaust system and lots of energy is wasted, internal combustion engines are highly inefficient thus, so this wasted energy is utilised to turn a turbine shaft that in turn spins a compressor which collects atmospheric air and compresses it so that a larger volume of air can be inducted into the same capacity cylinders, so for example if a cylinder has a volume of say 100cc, it can only hold maximum 100cc of air , but we can use this wasted energy and use it to force another 100cc of air into the cylinder, so called boosting, by stuffing 200cc of air into a cylinder of 100cc capacity, and doubling on our fuel, we are effectively creating an engine which is more or less equal to 200cc engine from a 100cc engine , thats my understanding, of course lots of others things need to be considered such as rise in temperature when air is being compressed.
However, biggest myth is that by having a turbo you get more power, of course you do, but only at the expense of extra fuel that can be burnt as more air (oxygen) is available inside a cylinder. This is no brainier, the wasted energy from the exhaust is only used to spin the compressor, to force feed air into cylinders. It does nothing to save on fuel economy, it does complete opposite, but provides higher power from a smaller engine capacity.
But what if we were to use exhaust gasses or this wasted energy to run a turbine wheel and couple its output shaft to an electrical generator, that in turn generates pure electrical energy from this otherwise wasted thermal energy, and can assist engine drive, it could for example be set up in such a way that energy generated from the generator drives an electric motor that assists engine, so you may perhaps attain 10% (just a rough guess) more from your fuel efficiency. Can we call it condensing Engine as in condensing boilers! ( Trouble is we will need a drain for our condensate!)
Turbos do spin at fairly high speeds like 100,000RPM, which obviously means they cannot be coupled directly to a generator, things in the generator would just fly apart, so it could be geared down to lower RPM and provide higher torque to drive an electric generator that could yield a few tens of kilowatts of electrical energy to assist mechanical energy from the engine, a computer could control the best gear ratio to provide maximum efficiency from wasted exhaust gasses.
However, biggest myth is that by having a turbo you get more power, of course you do, but only at the expense of extra fuel that can be burnt as more air (oxygen) is available inside a cylinder. This is no brainier, the wasted energy from the exhaust is only used to spin the compressor, to force feed air into cylinders. It does nothing to save on fuel economy, it does complete opposite, but provides higher power from a smaller engine capacity.
But what if we were to use exhaust gasses or this wasted energy to run a turbine wheel and couple its output shaft to an electrical generator, that in turn generates pure electrical energy from this otherwise wasted thermal energy, and can assist engine drive, it could for example be set up in such a way that energy generated from the generator drives an electric motor that assists engine, so you may perhaps attain 10% (just a rough guess) more from your fuel efficiency. Can we call it condensing Engine as in condensing boilers! ( Trouble is we will need a drain for our condensate!)
Turbos do spin at fairly high speeds like 100,000RPM, which obviously means they cannot be coupled directly to a generator, things in the generator would just fly apart, so it could be geared down to lower RPM and provide higher torque to drive an electric generator that could yield a few tens of kilowatts of electrical energy to assist mechanical energy from the engine, a computer could control the best gear ratio to provide maximum efficiency from wasted exhaust gasses.
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Right I have been searching for the truth, and found out that any mass of gas if kept at constant volume, i.e. if you seal it in say a canister, the number of molecules or atoms of that gas remain constant but pressure increases or decreases with temperature. that means pressure and temperature are directly proportional to each other, though in a turbo air is forces into a given volume of space, where it gets compressed, it heats up due to action of compression, but compressing air itself is another way of making the air denser, because if you pack more air or gas in a given space, you are effectively making its density increase, pushing more mass of gas into that same amount of space increases its density but this also creates heat in doing so.
Now if we stop our turbo pushing any more air into our given volume of space, which could be our inlet manifold, so we stop pushing in any more air in this given space, we cool it through an intercooler, by doing so we do not lose mass of that trapped compressed air, but we lose some pressure as that trapped air cools down, the number of atoms remain constant, so we may lose some pressure, but mass of that air is still constant, only the pressure is proportional to its temperature, so now i understand that intercooler may drop the pressure, but mass of air remains same.
This really answers my question as to why use an intercooler as dropping temperature would reduce pressure and we all assumed pressure equals density, but it is not, since volume (given space) remained constant. I or we have been thinking wrongly that when you cool air, pressure drops, and you also lose mass, (density) but you don't necessarily lose mass. Not in this situation, because mass is trapped and has no where to escape, it can only escape when inlet valve opens and fills into a cylinder, and as soon as mass of air escapes, more is pushed in by the turbo and cooled through an intercooler.
In open space, this would not be the case, as mass is able to move freely, and is not contained within walls, so it can move freely and hence density can change whereas in sealed pipework and chambers and manifolds, mass cannot escape other than when we want it to escape into say the cylinder on an induction stroke.
This is back to basic physics, which i missed when I was at school, because back then such things like Boyl's Law didn't interest me and I used to skive many lessons.
here is a link to brush your brain: also the article explains that heat makes the gas atoms or molecules move faster when heated, so faster they bounce about more pressure they creat. But mass remains constant.
http://www.passmyexams.co.uk/GCSE/physics/pressure-temperature-relationship-of-gas-pressure-law.html It would also be wrong to say that cool air is denser, since we know air is not very dense on high mountain tops where it is very cold. this is not because of temperature but because of air pressure, high up on a mountain the air pressure is less, so less air is packed per given volume, but at sea level there is more air pressure hence more denser air, as pressure forces more air atoms packed in that same given space. Also look at Boyl's Law. http://www.passmyexams.co.uk/GCSE/physics/pressure-volume-relationship-of-gas-Boyles-law.html
The thing to remember is that a turbo constantly feeds more mass of air into a confined space.
whereas a piston in a cylinder may compress the same mass of air into a lesser space (volume) so both compress air, but difference is turbo keeps adding more mass to achieve that.
Now if we stop our turbo pushing any more air into our given volume of space, which could be our inlet manifold, so we stop pushing in any more air in this given space, we cool it through an intercooler, by doing so we do not lose mass of that trapped compressed air, but we lose some pressure as that trapped air cools down, the number of atoms remain constant, so we may lose some pressure, but mass of that air is still constant, only the pressure is proportional to its temperature, so now i understand that intercooler may drop the pressure, but mass of air remains same.
This really answers my question as to why use an intercooler as dropping temperature would reduce pressure and we all assumed pressure equals density, but it is not, since volume (given space) remained constant. I or we have been thinking wrongly that when you cool air, pressure drops, and you also lose mass, (density) but you don't necessarily lose mass. Not in this situation, because mass is trapped and has no where to escape, it can only escape when inlet valve opens and fills into a cylinder, and as soon as mass of air escapes, more is pushed in by the turbo and cooled through an intercooler.
In open space, this would not be the case, as mass is able to move freely, and is not contained within walls, so it can move freely and hence density can change whereas in sealed pipework and chambers and manifolds, mass cannot escape other than when we want it to escape into say the cylinder on an induction stroke.
This is back to basic physics, which i missed when I was at school, because back then such things like Boyl's Law didn't interest me and I used to skive many lessons.
here is a link to brush your brain: also the article explains that heat makes the gas atoms or molecules move faster when heated, so faster they bounce about more pressure they creat. But mass remains constant.
http://www.passmyexams.co.uk/GCSE/physics/pressure-temperature-relationship-of-gas-pressure-law.html It would also be wrong to say that cool air is denser, since we know air is not very dense on high mountain tops where it is very cold. this is not because of temperature but because of air pressure, high up on a mountain the air pressure is less, so less air is packed per given volume, but at sea level there is more air pressure hence more denser air, as pressure forces more air atoms packed in that same given space. Also look at Boyl's Law. http://www.passmyexams.co.uk/GCSE/physics/pressure-volume-relationship-of-gas-Boyles-law.html
The thing to remember is that a turbo constantly feeds more mass of air into a confined space.
whereas a piston in a cylinder may compress the same mass of air into a lesser space (volume) so both compress air, but difference is turbo keeps adding more mass to achieve that.
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It's not really quite as simple as that. If you take a given volume of air at atmospheric pressure and do things to it, the mass (of air, hence of contained oxygen) will, indeed, not change. However, the mass of air that enters the engine cylinder will be determined by the temperature and pressure after you have done those things (compressing, heating, cooling etc.) - and hence is not necessarily the same mass as you started with.
As I've said a number of times, I think what actually happens in practice is crucially dependent on what happens to the dynamics within the cooler (flow rates, pressures and resistances to flow etc. in various parts). For example, if it were a sealed container, then cooling the air would certainly result in the pressure falling by the expected amount (and the mass remaining constant). However, the real situation is not a 'sealed container' but, rather, is a 'continuous flow' situation in which the compressor is constantly trying to push high pressure air into the cooler (and the cooler is trying to push gas into the manifold/cylinders) - so, dependent upon how it actually works, the fall in pressure due to cooling might be immediately partially overcome by incoming high pressure gas (bringing in more mass of air).
The physics of all this is actually remarkably simple - just the 'universal gas equation', PV=RT (where R is a constant). This means that if you keep one of the three variables (P, V and T) constant and change a second one, the resultant change in the third will be proportional (one way around or the other) to the change in the second.
Kind Regards, John
I agree, it is a little more more complex and more involved than I could have explained in some simple terms, yes its a bit like the Ohms law where changing one element reflects changes on another if a third one is kept constant.
It is a whole lot complex if all three were varying for various reasons, and you are trying to work out which is changing which? The ECU must be struggling mad to come up with appropriate amount of fueling from one second to the next, as engine speed, acceleration (loading) etc all play a complex role in its decision making process.
But I now realise why an intercooler is necessary, its prime objective is to lower the temperature of the compressed hot air from the turbo, to stop detonation, the air is denser already by the action of turbo forcing more volume of air in a given space, this space is obviously not sealed as the compressed air (or air under pressure but at a lower temperature) is constantly moving through, i am sure whatever the final results of that air mass, at any given RPM, and at any engine loading, is all calculated by ECU to control the amount of fueling, with closed loop monitoring by means of lambda sensors and many other sensors used in controlling the fuel, you have the MAF (mass air flow) sensor, you have the atmospheric pressure sensor, you have the boost sensor, dump valve, and load sensor which is often a throttle position sensor as on a WOT (wide open throttle ) the ECU interprets as engine under load, yes I used to be into cars. But never owned a turbo.
It is a whole lot complex if all three were varying for various reasons, and you are trying to work out which is changing which? The ECU must be struggling mad to come up with appropriate amount of fueling from one second to the next, as engine speed, acceleration (loading) etc all play a complex role in its decision making process.
But I now realise why an intercooler is necessary, its prime objective is to lower the temperature of the compressed hot air from the turbo, to stop detonation, the air is denser already by the action of turbo forcing more volume of air in a given space, this space is obviously not sealed as the compressed air (or air under pressure but at a lower temperature) is constantly moving through, i am sure whatever the final results of that air mass, at any given RPM, and at any engine loading, is all calculated by ECU to control the amount of fueling, with closed loop monitoring by means of lambda sensors and many other sensors used in controlling the fuel, you have the MAF (mass air flow) sensor, you have the atmospheric pressure sensor, you have the boost sensor, dump valve, and load sensor which is often a throttle position sensor as on a WOT (wide open throttle ) the ECU interprets as engine under load, yes I used to be into cars. But never owned a turbo.
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Indeed, I think we are all (perhaps not EFLI!) agreed that this is the main answer to your original question.
As you go on to say, I'm sure that the ECU, with the help of all the sensors, must do all sorts of clever things to keep control of this situation, although I suspect that it probably does not have much (if any) control over what the compressor and intercooler are doing. However, I think that turbos were around before the days of all this new-fangled and very complex electronics, so they must have found much easier ways to do it.
Kind Regards, John
I forgot to add that by lowering the temperature, your ecu is able to adjusts timing advance curve, just before the point of detonation, in conjunction with feed back from knock sensors, apparently further advance the timing gets more torque is produced, so to maximise engine performance cooler the air better it is, Mercedes F1 must have got the right set up as at the moment no one can come near them, something they figured out over years of research.
BTW, no regrets for missing classes during my school days, sure I had better things to do then, little did our masters knew that we would be able to catch up on knowledge from internet or google!
BTW, no regrets for missing classes during my school days, sure I had better things to do then, little did our masters knew that we would be able to catch up on knowledge from internet or google!
If you say so
As I've said, there are so many complicated interactions that I would not attempt to guess what the overall situation would be. Quite apart from what it means in terms of timing, lowering the temperature will, per se, have the potential to increase density, hence more mass of oxygen per unit volume, but will also lower pressure, having the opposite effect.Kind Regards, John
I searched google and came up with this link and it explains how cooling actually yields more power, see particularly no 3 para.
http://www.enginebasics.com/Advanced Engine Tuning/Intercooler.html
http://www.enginebasics.com/Advanced Engine Tuning/Intercooler.html
Interesting. I think one of the things that article illustrates is that, as I have been suggesting, the design of the intercooler (i.e. 'what goes on in it') is very important in determining exactly how it performs.
Kind Regards, John
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Not wishing to derail the derailment, but I though the idea of a turbo charger is to improve the power to weight ratio of an engine rather then to make it more efficient. After all if you want to fit twice as much oxygen in your cylinders you can just double the cc of the engine. But overall 3 cylinder 1.0l engine with a turbo is lighter than a v6 2.0l. Therefore possibly cheaper to make and better MPG even if the efficiency is slightly lower.
I don't disagree with that - other, perhaps, than the "rather" - since power-to-weight ratio is really just one aspect of 'efficiency'.
True, but the issue probably is that you couldn't have a switch on your dashboard (or an automated equivalent) which changed the number of cylinders and the weight of your engine - and if the engine always had "double the cc" (and corresponding increased weight), it would probably be very thirsty/inefficient at low speeds and/or when the load on the engine was low.
... similar, I imagine, to the reason why supersonic fighter jets (and, I imagine, Concorde in its day!) have after-burners, rather than double-size engines and/or twice as many engines.
Kind Regards, John
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