A2A (air - to - air) Intercoolers

... to be continued ...

SEE DIAGRAM BELOW

The supercharger (1) compresses the air that it receives from the airbox (not shown). When air is compressed, its temperature rises. Also, the hot supercharger is in direct contact with the air, which also adds heat to the charge air (2).

The hot charge air (2) is piped directly to the intercooler (3). The charge air is hotter than the intercooler (3), and heat flows from the charge air into the intercooler (3). The temperature of the intercooler (3) rises, and the temperature of the charge air falls.

The cooled charge air (4) exits the intercooler (3), and is piped into the intake of the engine (5).

The cooler charge air prevents damaging detonation from occurring in the engine combustion chamber.

Each litre of air that passes from the supercharger --> intercooler --> engine transfers heat into the intercooler, which acts to raise the temperature of the intercooler.

Ambient air (6) flows through the intercooler (3). Since the ambient air is cooler than the intercooler, heat will flow from the intercooler into the ambient air. The ambient air is therefore heated as it passes through the intercooler, and the heated ambient air (7) exits the intercooler, taking away heat, which lowers the temperature of the intercooler.

The lower the temperature of the ambient air (6), and/or the greater the amount of ambient air that flows through the intercooler, the more heat that will flow from the intercooler into the ambient air. The cooler that the intercooler remains, the more heat will flow from the hot charge air (2) into the intercooler, and the cooler that the air exiting the intercooler (4) will be. The cooler and denser the charge air (4) is, the more power the engine can make.

The MAF (mass airflow sensor), located between he airbox and the supercharger, calculates the amount of air that is going into the engine. The ECU uses this information to determine how much fuel to inject into the engine to correlate with the amount of air going into the engine.

An intercooler that flows better (less restrictive), allows more air to flow through it. A less restrictive intercooler also decreases "parasitic losses" at the supercharger, which allows the supercharger to be more efficient and run cooler, which decreases the thermal load on the intercooler.

An intercooler that has greater mass can "hold" heat spikes by absorbing the charge air heat without the intercooler climbing rapidly in temperature. An intercooler with less mass will rapidly rise in temperature, until it is equal in temperature to the hot charge air. Since the hot charge air is then equal in temperature to the intercooler, heat will *not* flow from the hot charge air to the intercooler, and the intercooler has reached a state known as "heat soaked." It is no longer cooling the charge air.

An intercooler with greater mass will continue absorbing heat because its temperature will not rise rapidly. This allows the ambient air (6) time to cool down the intercooler, instead of allowing the heat to pass to the engine through the charge air (4) exiting the intercooler.

Pros: unlimited supply of ambient air (6), simple installation, lighter than A2W, no maintenance. Direct heat path from supercharger --> intercooler --> ambient air.

Cons: adequate ambient airflow is required to keep the intercooler temperature low. When an A2A intercooler is located above-engine, it can be tricky to get enough airflow to the intercooler. Additional air ducting is necessary. Low mass intercoolers are incapable of absorbing major temperature spikes without becoming "heat soaked."

Possible problems: a) intercooler too restrictive, b) intercooler mass too low, c) not enough ambient air to cool the intercooler.

 

A2W (air - to - water) Intercoolers

... to be continued ...

SEE DIAGRAM BELOW

An A2W (air to water) intercooler works on a similar principle, but the path from hot charge air (2) to hot ambient air (10) is different.

Like an A2A intercooler, the path from supercharger (1), to hot charge air (2), to intercooler (3), to cool charge air (4), to the engine (5) is direct.

Also like an A2A intercooler, the hot charge air (2) heats up the intercooler (3) as heat flows from the hot charge air into the metal of the intercooler (3).

Water is circulated through an A2W intercooler (3), back to a radiator via a hose (6), through a remotely mounted radiator (7), then back through a hose (8) into the intercooler (3).

The intercooler temperature rises when it contacts the hot charge air (2). The cooler water within the intercooler (3) absorbs some of the heat from the warmer intercooler, then is pumped to the remotely located radiator (7).

The warmer water entering the radiator (7) contacts the cooler metal of the radiator, and heat flows from the water into the radiator. Water that has shed some of its heat then exits the radiator, where it is pumped back to the intercooler.

The now warmer radiator (7) is in contact with ambient air (9) that flows through the radiator. If the ambient air (9) is cooler than the radiator, heat will flow from the metal of the radiator into the ambient air, which will rise in temperature (10) and exit the radiator.

When the water temperature is too high to absorb significant heat from the hot charge air (2), the A2W intercooler is "heat soaked."

Pros: H2O is capable of absorbing large amount of heat. In a very high horsepower / high boost situation, water can temporarily absorb a large amount of heat. Good choice for short duration events such as drag racing.

Cons: Once the H2O is hot, it needs to shed heat via a radiator. Radiator competes for cool ambient air with the car's engine radiator and oil coolers, and therefore won't be as efficient as it would if it was exposed to cooler ambient air. The water in the system is heavy (8.34 lbs per gallon). System can fail by leaking. System can fail by pump mechanical failure or electrical failure. System is in constant contact with water, and is prone to internal corrosion. Not the best choice for sustained events such as road racing. Complexity of system demands greater installation time and cost. Less direct heat path: supercharger --> intercooler --> water --> radiator --> ambient air.

 

So you're saying...

Scrap that I just copied and pasted!! the only heat transfer I know is the image I created bellow for WWF (now E)

 

Pretty good basic explanation. A couple of possible points:
1. The radiator in the A2W case need not be behind the vehicle's radiator - it could be in front of it (as with an A/C radiator), or located separately (as with the Exige oil coolers.)
2. Because air does not need to flow through the intercooler, no supply of ambient air need be made available to the intercooler itself, which may be beneficial in some circumstances (such as where there is not enough air supply to the engine bay to provide both for the engine and an intercooler.)

I like the point about short versus long term races - it's easy to overlook that because water is your medium in an A2W intercooler, it can retain a substantial amount of heat by itself, and if the water is not fully cooled on its pass through the radiator, it will not be as effective when it gets back around to the intercooler.

You also didn't talk about the number of rows in the intercooler itself and how that matters.

Is it worth doing an article on heat and engines in general (i.e. why you want a cooler charge, what causes detonation and how it relates to heat, what a phase change cooler does and how it differs from an intercooler?)

 

Pretty good basic explanation. A couple of possible points:

Excellent points. You have pinpointed one of the biggest "pros" of the A2W intercooler: the possibility of locating the radiator to a more advantageous location.

Yes, an A2W radiator can be in *front* of the engine radiator, but remember that the heat that is shed from the A2W radiator is now raising the temperature of the air entering the engine radiator (which is known to be marginal as it is).

I'll add more about the construction characteristics of the different intercoolers. To the extent that it doesn't get into proprietary information, I'll explain the basics.

Thanks for your ideas!

 

Since you're giving a lesson, I'd add:

In your diagram of A/W intercoolers, most OEMs use a sandwich style charge cooler rather than a remote mounted aftermarket A/W cooler. They do this to mitigate pressure loss and intake volume, increase efficiency, etc... That would add a pro to A/W setups for superchargers, ie less pressure loss and better throttle response-- which in turn means the IC doesn't have to "work" as hard. Those OEM applications are also going to be pretty lightweight since the charge cooler core is small by comparison... Just say'n...

Also, you need a much greater volume of air (like air from the frontal area of a moving car) to make the A/A IC exceed the effectiveness of an A/W system with much less volume of air (such as that drawn through with a fan) due to the design on the two heat exchangers... The light weight water radiator on the A/W system simply doesn't need the volume of air that the A/A IC does to perform...

No doubt that you're correct in that the A/A IC is more efficient in ideal situations. The exige/elise is far from ideal though... regardless of whether you're road racing or drag racing, you'll be hard pressed to beat the effectiveness of a well sorted A/W system on the lotus. The question is, can you "get by" with an A/A setup and be satisfied? If you're looking for max power, then you're going to have to use the A/W on our cars...

Cheers,

Phil

 

opcorn:

 

great stuff

 

I endorse your duct work all the time to promote airflow. It's soooo important on the A/A setups. What I am saying is that airflow if more critical on the A/A setup than an A/W setup. I find a bit of humor in folks upgrading their IC and not upgrading airflow... That is the point.

The front mounted water heat exchangers I've seen are all upstream of the engine radiator or in place of the oil coolers. Oil coolers replaced by laminova/relocated. I can't comment as to the impact the heat exchanger has on engine temps when properly executed, as I haven't ran that configuration. I believe several folks do with success though...

Again, the A/A is fine if it meets your power goals. I think you'll be very hard pressed to meet or exceed 50% efficiency with A/A on our cars (perhaps not impossible with enough aftermarket help). I've stated that even before I built an A/A setup for my car. I contend that despite the greater *potential* efficiency of the A/A setup, if you want greater than 50% efficiency to achieve greater power levels, you have to go to A/W on our cars... There's just no way to get the airflow to the A/A IC to get into the 70s+ like front mounted A/As do... On the otherhand, it's not too difficult to pull that off with the A/W with Lotus packaging.... again, it's about power goals...

 

The front mounted water heat exchangers I've seen are all upstream of the engine radiator or in place of the oil coolers. Oil coolers replaced by laminova/relocated. I can't comment as to the impact the heat exchanger has on engine temps when properly executed, as I haven't ran that configuration. I believe several folks do with success though...

Yep, the setup I am running is the same as AJ, and I believe Frank (although he has a 4th heat exchanger in the rear).

The side oil cooler spot units are PWR units and the water goes through them first so those kill most of the heat...the remaining water goes through a core directly in front of the front clam opening where the rest of the heat gets killed. This air then goes through the radiator core. I don't think any of us have had engine temp issues, it's definitely warmer now but I am getting engine temps around 195-200 with proper airllow. I would imagine moderate boost with the TVS wouldn't need a third center core and just use the two side ones leaving the radiator with clean air.

Lastly, less of an issue of with our cars but more with front engined...there is the issue of the volume of air tract for response. A front aftermarket A/A like on an STI has lots of tubing before it gets back to the engine...more than on the stock top mount and enough to be noticed on throttle tip in off boost. I really like the way my A/W feels on the Lotus...instant supercharger boost plus very little air length to move around.

 

Ever studied the Esprit SE Chargecooler system?

 

Dam dog, you guys are getting too serious, all I need to know is how much it costs (including taxes) and how fast it can go, the rest I leave up to you tech people rotfl

 

We run a 304 bhp Exige S with great success on an A2A intercooler.

When you start talking about huge power, I can see where an A2W would have application.

 

Your site constantly tempts me, but I am trying hard to wait to see how the MWR V6 conversion comes out. I want that torque!

 

The Esprit A2W system does not add any length to the intake tract, path is exactly the same with the non charge-cooled cars.

The radiators are stacked with the intercooler first, then AC, then engine cooling. It also has two oil coolers, on on each side of the rad stack (not in front of the other rads).

My intake air temp, measured directly after the intercooler, and only inches away from the throttle butterflies, is usually about 5deg.C above ambient, and rises slightly with boost, up to a max of 47deg. C (that I have seen).

The system had a mechanical coolant pump and a separate coolant system. The pump was driven off the oil pump (1:2 ratio with the crank). Though I recently replaced it with a Jabsco Centripuppy electric pump. See electric pump comparisons here Electric Chargecooler Water Pump / Adding more water / Jabsco / Johnson

My car is running ~1bar boost (14.7psi), though at my altitude the turbo is allowed to spool up to the max of 2.25bar abs MAP (subtract baro at 5300ft and a lotus fudge factor), my dash mechanical gauge pegs at 1.25bar all the time. In that regime my turbo is actually not very efficient, and probably creating some extra heat, the chargecooler seems to do a really good job though.

 

opcorn: