Air conditioning the charge air. (math content)

Ford used this style of intercooler on the Lighning pickup for a few years. if i'm remembering right, the AC system cooled some water, which was fed into an air/water intercooler mounted under the supercharger.

JohnyHachi6 wrote: In reply to curtis73: Conservation of energy really doesn't apply like that to this problem. It's not like the A/C compressor is helping to spin the engine, it's allowing the engine to burn more fuel and thus make more power. If conservation of energy applied like you wrote, then how would a supercharger make additional power? Wouldn't you "spend more hp" driving the supercharger than you got back from compressing the charge?

Superchargers partially use otherwise wasted power. An A/C compressor uses engine HP to transfer heat. Any time you're working within one form of energy, the law of conservation applies.... like using a windmill on your electric car. The drag and inefficiency of the windmill means you'll never recover as much energy as you use moving the windmill through the air. But, putting regenerative braking on the wheels to recover energy that would otherwise be wasted IS a benefit.

You're using an engine-driven appliance to generate a heat differential, then reversing that heat differential in the engine. If it takes 10 hp to drive the A/C compressor, you won't get a 10 hp benefit from the cooler air. That would be perpetual motion.

curtis73 wrote: An A/C compressor uses engine HP to transfer heat.

Yep, with you so far.

Any time you're working within one form of energy, the law of conservation applies.... like using a windmill on your electric car. The drag and inefficiency of the windmill means you'll never recover as much energy as you use moving the windmill through the air.

And this is where you're slipping up.

The A/C compressor isn't being used to drive the car. The amount of extra power the engine can make with cooled charge is greater than the amount of energy it takes to turn the compressor.

Let's look at it this way. It can take, at the very most, 10hp to turn an A/C compressor, given how much power can be transmitted via a typical belt. In reality it's generally less than that, but let's use this as a worst-case example.

Will the engine be able to make more than 10hp extra by having the charge air cooled with a 32 degree working fluid? All signs point to yes!

This is not about driving the vehicle with the refrigerant. This is about getting cooler charge so the engine can get more air/fuel crammed in and run at more optimal ignition timing settings before running into detonation.

I can use your argument to say that turbochargers don't work. Turbos don't work off of "free energy", they quite measurably raise exhaust manifold pressure as proof that the engine is working to spin the turbine. In fact the pressure differential across the engine is generally far, far higher than a naturally aspirated engine. Therefore, in theory a turbo engine shouldn't even be able to run!

Let's look at it this way. It can take, at the very most, 10hp to turn an A/C compressor, given how much power can be transmitted via a typical belt. In reality it's generally less than that, but let's use this as a worst-case example. Will the engine be able to make more than 10hp extra by having the charge air cooled with a 32 degree working fluid? All signs point to yes! This is not about driving the vehicle with the refrigerant. This is about getting cooler charge so the engine can get more air/fuel crammed in and run at more optimal ignition timing settings before running into detonation.

Ah... but you are assuming that the A/C system can absorb enough BTUs to effectively lower the temps to 32 degrees (or lower them appreciably at all.)

Take a look at the BTU rating of typical automotive A/C systems, then look at how many BTUs can be carried by 500 CFM of ambient air. I think you'll find that the 10 hp you spend on the compressor will maybe get you 1-2 hp in return, meaning a net loss of 8-9 hp. The system will rapidly heat soak and kick off the compressor. Even if you set up water jets on the condenser I think you'll easily exceed the capacity of the system by drawing that much ambient air over the evaporator.

I'm not talking about the compressor driving the car, I'm talking about simply within the a/c system. You are using 10 hp to make a heat differential. There is no way you can effectively recoup that 10 hp, especially considering the losses to friction, heat soak from the hot underhood air, etc. What you're trying to do is use 10 hp to create a heat differential, then recoup that 10 hp with that same heat differential you just made when it converts back. Not gonna happen.

It's completely possible. Superchargers are driven by the same method that drives an AC compressor.

While I agree that it will be hard to make power this way, physics says it is possible. You aren't putting energy from the AC compressor into the engine again, you're using it to burn more fuel.

Um, I'm probably over my head here, but doesn't the evaporator take heat out of the refrigerant charge? So wouldn't the OP want the condenser in the intercooler "box" instead (adds heat to the refrigerant)... ?

Also, I think the coolest I've seen charge air get was about 34 degrees, and that was with a piddly amount of CFM. If we're talking boosted (positive manifold pressure) air going through this thing, you'll be lucky to get any kind of air temp drop at all. That's why liquid intercoolers use water/coolant (liquid) as opposed to a refrigerant (gas/liquid)...

In reply to Javelin:

Evaporator is the cold part of an A/C system. The liquid-vapor phase change (evaporation) process absorbs heat, making it cold.

I agree that if you want a really cold charge, a liquid cooler is the best way to go.

curtis73 wrote: Superchargers partially use otherwise wasted power.

That's false.

Again, in this case the supercharger is raising the manifold pressure to let in more air. The A/C compressor is lowering the manifold temp to let in more air. They both use crank hp, neither of them directly produce power, both of them can result in higher net engine power.

curtis73 wrote: Superchargers partially use otherwise wasted power. An A/C compressor uses engine HP to transfer heat.

Both are run off of an engine driven belt. There is power being transfered. Usuable power.

Coefficent of Performance for most air conditioning units are around the 3-3.5 range. Which means it can move 3 units of heat for every 1 unit consumed. It's a heat pump. It's moving heat, not generating heat more heat than what is being supplied.

I was thinking about all of this a/c cooled intercooler but a standard air cooled intercooler has so much more potential for substatially cooling the air. That's not to say it can't be done.

curtis73 wrote: Ah... but you are assuming that the A/C system can absorb enough BTUs to effectively lower the temps to 32 degrees (or lower them appreciably at all.)

Fortunately, it doesn't need to.

Take a look at the BTU rating of typical automotive A/C systems

Quick Googling says 10,000-20,000 BTU depending on system. (Quote for reference: "The A/C system on my Acura Type R is rated at 14,000, and it definately puts a good load on the engine-probably 5 HP at least.")

Let's go with 10k for pessimism's sake. And let's stick with 10hp. Pessimism.

then look at how many BTUs can be carried by 500 CFM of ambient air. I think you'll find that the 10 hp you spend on the compressor will maybe get you 1-2 hp in return, meaning a net loss of 8-9 hp.

Let's say you have a turbo flowing, oh i don't know, 60lb/hr of air. (That's a decent sized turbo). Let's say the air exiting the turbo is, oh, i don't know, 240degF. (SWAG number here) My quickie math has us able to cool the air down to the freezepoint and have plenty of headroom left.

What you're trying to do is use 10 hp to create a heat differential, then recoup that 10 hp with that same heat differential you just made when it converts back. Not gonna happen.

What you are missing is that a turbo engine will be able to make a lot more power with cooler air charge than mere density calculations can dictate, since turbo engines here in the real world (no ultra-awesome witches' brew) are detonation-limited.

I wish people would read all of the comments before posting because as said earlier you are using that 10 hp to make colder intake air which is more dense which allows you to burn more fuel LIKE A SUPERCHARGER. Yes you will get some more horsepower out of the engine. Will it overcome the losses associated with the refrigeration system? I don't know.

Is this a turbo or supercharged engine? If so you would want the evaporator in the intake tract right before the Carb/MAf/etc and after the intercooler.

If a N/A engine go for a cold air intake and again put an evaporator inline with the intake tract right before the Carb/MAF/etc

I say try it and if it doesn't work then you can use the existing evaporator in the intake tract as an air-water cooler by adding a pump, some hoses and a cooler full of icy water.

Thought here was to eliminate the intercooler in lieu of blowing the charge air through the evaporator. This is because there is very little air flow in the place where the air-to-air intercooler would be in my particular application (V8 in the back of a hatchback).

In my case, I'm looking at using a turbo, but turbo or supercharger, the principle is the same, I'm boosting to 8+lbs above ambient. It would be nice to cool it down a bit so my motor won't have to be any more retarded than it already is. (hehe, little tuning joke there)

And on paper, it looks like the AC evap charge air chiller IS a power adder. Barely. Yeah, there's lots of assumptions involved, and given that it is a tiny gain and a lot of fab work (making the box to house it) I'm just going to find a place to stick a junkyard i/c, duct some air off the roof or fender and call it done.

I bet I COULD make it work reasonably well if I used the OTHER A/C evap too, then I'd have 30k+ BTU/h at my disposal. Yeah, you read that right, the other A/C evap. This car has 2 engines, and could have 2 AC systems if I don't scrap them for the aluminum.

Your alternative is a water/air intercooler.

The way I see it, A/C intercooling is just a badass liquid/air intercooler because it uses the heat of evaporation to be able to pull temps below ambient.

Knurled wrote: Your alternative is a water/air intercooler. The way I see it, A/C intercooling is just a badass liquid/air intercooler because it uses the heat of evaporation to be able to pull temps below ambient.

Problem is, you then need a badass air/liquid cooler (and a refrigerant capable of shedding that heat quickly enough) to make it work... and it won't.

curtis73 wrote:

Knurled wrote: Your alternative is a water/air intercooler. The way I see it, A/C intercooling is just a badass liquid/air intercooler because it uses the heat of evaporation to be able to pull temps below ambient.

Problem is, you then need a badass air/liquid cooler (and a refrigerant capable of shedding that heat quickly enough) to make it work... and it won't.

Ford did it in the lightning.. i forget what model years, but they used a water/air intercooler that used the AC system to cool the intake charge.. the google is currently failing me in finding info on the setup they used..

novaderrik wrote: Ford did it in the lightning.. i forget what model years, but they used a water/air intercooler that used the AC system to cool the intake charge.. the google is currently failing me in finding info on the setup they used..

Yup... and that doesn't mean it made a net increase in power. It might mean that they covered their asses when they couldn't figure out how to lower the compression enough to pass HC emissions at idle, but they did it.

Chrysler also tried a turbine-powered car. Tucker also took Howard Hughes' advice. Harley Earl was GM's greatest gift until they fired him because he was gay. Just because a manufacturer put it on the street doesn't mean its a proven fact of science. It could mean that they had a shortcoming which had to be spun into a marketable ploy. Remember Saab's variable compression? How about the self-inflating tire from the 50's? Or how about the multi-billion dollar "Lean Machine" from GM that was so huge that it was a sponsored EPCOT attraction?

OEM doesn't mean that it works, it means that they have made people believe that it works. Do I need to reference any of the Hybrid threads on the engineering forums?

I really do respect you all, and I do believe that this is a viable topic, but I urge you to post this topic over at www.eng-tips.com. Its a forum of the finest engineering minds I've ever met. My guess is that you will be instantly banned for the "remedial implausibility" of your post. Heck, I've been banned once and I have a mechanical engineering degree. My only hope of staying a member is by not posting. They weed out the weak like Hyenas weed out the Wildebeests.

My recommendation actually comes with Kudos... its rare that I refer questions to that site (and the first time I have done so on GRM) but I guarantee that they will answer things quickly, tersely, succinctly, and with android-like impartiality.

... that is, if they don't ban you first. It depends on whether or not you're a Hyena or a Wildebeest.

It may not work, it certainly wouldn't be worth it, but it absolutely does not violate thermodynamics. No more than any belt driven power adder. You would be burning more fuel and more oxygen so there would be more matter available to turn into energy.

Challenge Car? Scale-up a cool can.

I love the non-sanity going into this project. I mean, once you've put that Lincoln engine somewhere between the rear tires, what else can you do to stretch the limits of auto-orthodoxy? Keep it up! But, in this regard, you might just want to stick a big ol' semi intercooler in the back window and turn the rear side windows into gynormous NACA ducts. You're gonna have to firewall off a good part of the passenger compartment anyway. And with that much power, who's gonna care about aero?

I don't think the system Ford came up with was ever put into production, I think it was for the Lightning concept on the 04+ body style.

If I recall correctly it used a regular air to water intercooler setup, in addition to that the a/c system would keep some kind of anti-freeze solution very cold. When the system was triggered you had some short time period (30s to 1 minute I believe) of extra power.

Hmmm... maybe it's just me, but I found eng-tips to be useful, and the participants seem to be knowledgeable with good practical experience.

Hyenas? Nope.

Interestingly enough a quick search there found a discussion on there about a similar question with no evidence of any banning.

Hyenas devouring a wildebeest

I didn't read through the whole thread (2 1/2 year old is ready for bed), bit is seems there are at least a few over there thinking there could be a net gain.

jstand wrote: Hmmm... maybe it's just me, but I found eng-tips to be useful, and the participants seem to be knowledgeable with good practical experience. Hyenas? Nope. Interestingly enough a quick search there found a discussion on there about a similar question with no evidence of any banning. Hyenas devouring a wildebeest I didn't read through the whole thread (2 1/2 year old is ready for bed), bit is seems there are at least a few over there thinking there could be a net gain.

get the liquid for the intercooler nice and cold when you aren't on the throttle and use that stored "coldness" to build power when you go WFO and kill the AC compressor with a switch when you do want the added power.. it won't work for something like a 5 mile land speed run at Bonneville, but it would work for a good chunk of a 12 second drag strip pass or from corner to corner at an autox course or even a tight road coarse with a lot of heavy braking zones.. the extra drag from the compressor would even add some engine braking..

Curtis, no offense, but you just got told..

What about just using Nitrous Oxide injection to cool the charge air?

How come you guys with the turbos and a need for cooling don't fill the gutted doors with radiators and an ice/salt mix?

Probably enough space to keep a few brews cold for after the race.