Intercooler before turbo?

[Scotracer]

would it be better to put the intercooler futher along the intake tubing so it would be colder when it enters the engine. (i never can interpret what my head is thinking)

Largely irrelevant. The distance between the throttle body and the intercooler is largely dictated by the ergonomics under the bonnet (or hood, if you're American) - a compromise between being close to the intake and getting max air flow across the 'cooler. Usually the latter is the better thing to strive for as it makes the biggest difference.

[xpensive]

As so many times before, DK is entirely correct, the need for an intercooler is to bring the temperature down after it has been heated up by the sheer compression from the turbo, or mechanical compressor for that matter.

The reason why you want to reduce the temperature of the compressed intake air is really to shrink it, when it's all down to how many Oxygen molecules you can burn together with the fuel in the combustion chamber.

I can still remember the good old turbo days in the mid 80s, when they packed Nelson's gigantic intercooler with dry ice and sprayed all the pipings with a fire extinguisher before that one lap quali-burst at Österreichring.

[kilcoo316]

But i wonder what would happen if you send the air to the intercooler directly from the intake and then to the turbocharger. Would you get similar results?

You would* get a greater massflow rate through the system, but you would also have much higher temperatures at the inlet manifold.


The best performing** system would have coolers both pre and post turbo.

(For higher massflow rate @turbo and lower manifold temperature)


*as others have pointed out, a standard air/air cooler will do very little as the temperature difference from pre-turbo air to ambient air is very small.

**in terms of engine power - says nothing for overall system efficiency.

[xpensive]

Again, what it's all about is shrinking the air after compression by cooling it, all in order to get the maximum amount of oxygene molecules into the combustion chamber for burning the gasoline.

[ISLAMATRON]

No need to cool that fluid, usually I use the windsheild wiper fluid system and get rid of the windsheild wipers and use rain-x, pretty simple actually.

Maybe I've just forgotten my thermodynamics since I left uni but how exactly are you reducing the temperature of the intercooler by supplying ambient fluid to an ambient intercooler? If the intercooler is situated well enough in the engine bay heat soak wont be an issue.

Intercooler is not ambient, the air is heated by the turbo and then some of that heat is exchanged to the intercooler(its purpose). The fluid absorbs the heat when it evaporates off of the intercooler, the ambient airflow thru the intercooler is not enough to soak up all the heat so the fluid helps. All intercoolers get heat soak no matter where they are put in the engine bay, I only front mount them and they still get heat soaked.

Sometimes I direct the a/C condensate to the Intercooler, super efficient and at no cost.

[ISLAMATRON]

wouldn't it be more efficient to put the intercooler close to the throttle body/carburetor so that it would be cooling while traveling the intake tubing andthen cool off considerably than cool it imeadietly and lose some of that cold to the engine heat?

Good luck cooling that intercooler placed next to the throttle body, th cooling thru the pipes is neglegible compared to thru the intercooler

Edit: yep exactly what Scotracer said.

[riff_raff]

Intercoolers, as the name implies, are traditionally located between the super/turbocharger compressor outlet and the next compressor stage, or the engine inlet. But that device would more correctly be called an "aftercooler".

Charge coolers have both benefits and drawbacks. Since all supercharger compressors, whether dynamic devices like turbos or positive displacement devices like Rootes or Lysholms, have efficiency losses while compressing the intake air charge, so they naturally cause heating of the intake air. For a diesel engine this is not normally a problem, but for a gasoline engine a hot intake charge can cause detonation.

A charge cooler can reduce the intake charge temperature, but it will also decrease intake charge pressure, create intake duct flow losses, and the heat energy lost to the cooling airflow is power wasted.

The efficiency of an air/air heat exchanger is mostly a function of the deltaT between the two flows and the physical size of the exchanger core. Throttle response can be improved by minimizing the length of the intake plumbing. But the turbo compressor stability is helped by having a relatively larger total volume within the intake system.

As is typical with everything regarding an engine design, it's all about what is the best compromise. There's no free lunch.

Regards,
Terry

[xpensive]

When what it's all about is shrinking the air after compression by cooling it, all in order to get the maximum amount of oxygene molecules into the combustion chamber for burning the gasoline, one could imagine a similar device for an atmospheric engine.

Only, you need to cool the intake air to a temperature under the ambient, by use of some sort of chilling device, like a fridge or freeezer.

But I belive such a pactice is outlawed in F1 at least?

[alexbarwell]

Pre-cooling could be more effective if plumbed up to a high capacity refrodgeration unit, but that would probably cause more problems. As a what-if, if the turbo/supercharger compression was raised (higher pressure output) the act of compressing the air raising its temperature, then the intercooler which would have a greater effect on a higher temperature, but after the intercooler, LOWER the pressure fractionally which will further reduce the air temperature to the engine, but still higher pressure than atmospheric.
Remembering there are rules in some series about inlet charge temperatures - recall the other year that one of the F1 teams (renault/honda?) was disqualified from a race result due to fuel temperature being lower than permitted.

[xpensive]

I remember in the early turbo-years, Toleman was running Brian Hart's four cylinder engine, while being sponsored by Italian domestic-appliance supplier Candy.

There was talk of Candy developing a fridge-like intercooler for Hart, never happened, but would have been legal at the time I guess?

[Ian P.]

The basic idea of cooling the inlet air to an engine or turbo is a somewhat reasonable concept but in the real world ..... very limited applications. In the racing worls....not a chance.
If the turbo has a pressure ration of 4 to 1, net outlet pressure of 45 psig (300 kPa) an intake temperature of 20 deg C, the outlet temp. will be upwards of 180 deg C even with outstanding efficiency. In order to put the cooling at the front end (ahead of the turbo) you should be able to guess at the temperature drop you would need to achieve the same effect.
Big advantage of the after turbo or inter-cooler is that the temp. difference across the cooler is HUGH. At a delta of 160 C deg. the cooler will be an order of magnitude smaller than if the difference were only 40 C deg. Try packaging the latter into a side-pod.

Is there still a case for pre-cooling the inlet??...well yes there is. Beyond ensuring the inlet air to the engine or turbo is as close to ambient as possible, there really isn't a place for inlet cooling in circuit racing.
One place where it does have a real application is in gas turbine power plants. Those subjected to high inlet air temperatures.

http://www.tas.com/

By judicious use of large chilling plants to cool the inlet air, the output derating at high ambient temperatures can be avoided and the net power available for sale is increased. Even after considering the power needed to run the chilling plant, it can still pay off in avoided additional units or better utilized smaller units.

[riff_raff]

Ian P,

Turbocharger compressors are dynamic devices, whose efficiency is subject to physical effects like fluid density. Cooling the working fluid (and thus increasing its density) ahead of the compressor can improve the performance of the compressor. But whether the penalties caused by this cooling process are worth the improved compressor performance is another matter.

If you ever saw a turbocharged, methanol fueled Champ Car engine during the 90's, you would have noted the fuel injectors ahead of the turbo compressor inlet. The reason for doing this was that Champ Car rules did not allow intercooling. So the engine designers put fuel injectors at the turbo compressor inlet to produce intake charge cooling due to the high latent heat effect of methanol.

The cooling and charge densifying effect of fuel latent heats is why even N/A F1 engines locate their fuel injectors as far up the intake runners as possible:



Regards,
Terry

[010010011010]

hi,

if you were to run a turbo engine on hydrogen then couldn't you use the fuel lines to precool the intake air before going into the turbo to increase its density. and there would be a significant cooling applied since hydrogen is a liquid at -252.87°C and so the precooler fed by the fuel lines would have to be somewhere near this mark. Providing they don't just shatter like china.

[majicmeow]

density before the compressor wheel hardly matters in most cases. Its the density in the cylinder that is most important. Instead of trying to get the air cold enough that, even with compression it is at a lower temp than ambient, why not let the cooler stay before the intake and then build on that?

An intercooler hardly gets colder than ambient in most cases unless its got a sprayer.

Just my 2¢

[riff_raff]

majicmeow,

With an engine that requires stoichiometric A/F ratios for best power, you are partially correct in your statement that trapped intake charge air density is important, since more more trapped oxygen molecules means more fuel molecules can be combusted. But since the power output of spark-ignited, Otto cycle engines is ultimately detonation limited, the charge temperature at the start of the compression cycle is also very important. If there were no detonation limit, then charge density could easily, and more efficiently, be increased by higher compressor pressure ratios rather than intercooling. As previously noted, while charge cooling results in a cooler (and thus denser) intake charge, it also adds weight, aero drag, engine package size, engine thermal losses, and intake charge pressure and flow losses.

Also, I would disagree with your statement that "density before the compressor hardly matters". With dynamic compression devices like turbocharger compressors, the mass flow is better with a denser airflow ahead of the compressor for a given pressure ratio. And as you noted, mass flow is what's really important.

Regards,
Terry