Is CO2 cooling a good idea?

[zelone]

Hello,
I am new to this web site, I am not an engineer, I just like to design and build my own ideas. I think this site will help with alot of them.

My question is about using compressed CO2 to cool a lower intake manifold on a Ford 302L engine. The engine has a Kenne Bell Twin-Screw type of supercharger which sits directly on top of the lower intake manifold. Because of this design, there is not much room for an intercooler. I have been considering building a CO2 cooling system which would operate similar to a N2O system. It would be activated by either a WOT switch or a manual override switch, which would activate a solenoid/valve to allow compressed CO2 to travel from the tank to a "rail" made from 3/8" steel fuel line. The line would be shaped like a "U" and be mounted over the lower intake manifold. Above each intake runner I would drill a small hole or seies of holes aimed at the lower intake. When the solenoid is activated, CO2 would spray on the lower intake manifold, cooling it significantly. I believe this can be put together for very little money. I would like some opinions and suggestions about this idea, before I spend the time and money. It will be completely removeable and will not changes the a/f ratio because nothing is being added to the actual induction. It shouldnt require any tuning. The engine control system should be able to sense that the air going into the engine is more dense and therefore add slightly more fuel to compensate.

Any suggestions are welcomed.
Thanks for taking the time to read this.

-Den

 

[Docengineheat]

It sounds as if the original intake manifold would be left unchanged; is that right? What you are describing sounds sort of like spraying a CO2 fire extinguisher on the manifold.

If that's the case, I suspect that the heat transfer through the intake manifold and into the charge air would be minimal. The reason intercoolers have thin walls and a lot of fins is to facilitate heat transfer. The intake manifold has a thick wall (relatively speaking) and no fins.

You could have some fun by taking an intake manifold and passing some copper tubes through it, and then running your cooling solution/gas through the tubes. You would certainly enhance the heat transfer. It might lead to some fuel puddling, though.

 

[patprimmer]

I have to agree with Docengineheat. The system you describe would cool the manifold significantly, but the heat transfer to the air charge would be very slow and ineffective. If you were at WOT for say 3 seconds, and thats a long time for a normal road car, I doubt if there would be a measurable change to the inlet air temp.

Also, I expect that the draft from the fan and the forward motion of the car might blow the CO2 around a lot, further reducing it's efficiency and the distribution of it's cooling effect. Some CO2 might even end up in the air intake if care was not taken to avoid that. This would have a detremental effect on power output.

Tubes through the manifold as Docengineheat suggests would work better at cooling due to the greater surface area, and better distribution accross all the air in the inlet charge, but it would also increase restriction to flow. To do this effectivly, you would need to build a plenumb with sufficient cross sectional area to accomodate the cooling tubes and still have good airflow. It would also workout quite expensive, and is actually a CO2 powered intercooler.

Regards
pat

 

[zelone]

Thank you for your input. I would generally only be using this system at the 1/4 mile track, where the length of time at WOT would hopefully not exceed 12.5 seconds. I would also consider using this before a run down the track, my theory is that if people use ice on an intake manifold in between runs to cool the intake down, then using CO2 in between runs to "freeze" the intake should be at the very least as effective as icing the intake. Ice on the intake between runs has shown to drop 1/4 mile time by 2 tenths of a second. I would think that freezing the manifold while the car is not running or while it is idleing before a run would have to show a similar, and hopefully better gain. I have considered making small pipes through the intake runners to allow the CO2 to cool the air at the center of the manifold. I am still trying to figure out how to do this cost effectively. Thanks again for your comments. More are always welcomed.

 

[TheBlacksmith]

I think the cooling effect of CO2 is vastly overrated. The CO2 may be a liquid in the bottle, and it converts to a gas when you let it out. This transformation requires considerably more energy than just warming up the CO2, hence the bottle gets very cold. Unless you can ensure the pressure drop/transformation occurs right at the manifold, you're missing the bigger effect. Dry ice works well, because it will sublimate under normal atmospheric conditions, converting directly from a solid to a gas, absorbing a significant amount of energy (heat).

Blacksmith

 

[strokersix]

I have plumbed hot water instead of hot exhaust gasses through exhaust heat crossover passages on several engines to improve driveability and cold weather operation. You might consider plumbing an evaporative cooling medium or perhaps ice water though the crossover to cool the intake. Assuming your intake has exhaust heat provision of course.

 

[ICman]

I'm no expert, but you might want to be careful with "freezing" and heating the manifold. Cyclic heating and cooling does strange things to materials, especially when it's done to extremes. Fasteners may loosen. The crystalline structure of the metal/plastic may even change, resulting in cracks, etc.

That said, I doubt if prepping an engine like you describe will do much, if any, damage. CO2 in your intake air stream is not good. CO2 and water form carbonic acid, which can be detrimental, also. That's why N2O is popular - Nitrogen is a rather inert gas, as well as in the air we breathe... and then there's the release of Oxygen to improve combustion.

 

[wildcatgeorge]

One of the best ways to cool an intake charge is to use
a seperate "cooling" system for the supercharger.

It would consist of a heat exchanger in the manifold
which would look like a mini radiator situated below
(between) the supercharger and the mounting point
on the manifold.

You would need a water pump, 12V electric will do,
(high volume) and plumbing to the second radiator,
which will need a fan for cooling, could be in front
of your radiator too.

Fill second radiator with 50/50 water/alcohol or your
choice of cooling medium.

This system will last a long time and need little
maintainance or cost to run efficiently.

my $.02 worth
Darrin

 

[zelone]

Thanks for all the advice.
Darrin, I would love to build the exact same setup that you mentioned. The design of the supercharger and the car it is in does not allow it to happen easily though. There is literally less then .5" of clearance between the supercharger and the bottom of the hood. The supercharger sits just above the lower intake manifold. Here is a link to a picture of the same setup that I have on my car. The discharge manifold comes from the top of the blower and bolts to the lower intake. A redesigned discharge manifold with a heat exchanger inside would probably help, but would also obstruct the airflow. It should also be noted that the discharge manifold is the main support structure for the blower itself which is kinda heavy. I would guess building a sheet metal discharge manifold out of thicker metal to be able to hold the weight of the blower with a heat exchanger inside of it, is still something to consider. I will look into this idea a little bit further. Thanks again everyone. Here is the link:

http://www.kenne-bell.com/Owners/TroyKimball/93 with kb.jpg

 

[wildcatgeorge]

I love a challenge!
Of the two points you make, one I knew you would
have, the restriction of the air flow, you must weigh
the benefit of cooler restricted flow air and hot unrestricted
flow, you might make more power on dense cooler air!

Also if the discharge is not directly blown down into the
engine, you have a place to attach an intercooler, as opposed
to the aftercooler I proposed, BTW the aftercooler could be
made in a manifolded capillary style, and be 1/4 to 3/8 " thick.
OR installed inside so it adds no additional height and plumbed
through a suitable location in the manifold, the latter of these ideas
is going to be very difficult, maybe impossible.

Good Luck
Darrin

 

[crashcraft5]

just a few things to consider, if this car is never driven in cold weather then the first step toward a cooler intake charge is to bypass the coolant flow through the throttle body is a simple matter of unhooking the two coolant lines that go through it and simply connecting them together, 2 wrapping the air intakes will slow engine heat transfer into your intake charge, it generally doesnt look pretty but it is cheep and works. option three is to remove the intatake and fabricate a heat shield between the lifter valley and the bottom of the intake to shield it from hot engine oil, we did this blocked the crossover passage for exsaust gases and coated the the bottom of the intake with ceramic paint then had the inside of the intake polished and coated with an other ceramic to stop heat transfer. on my supercharged 87 t-bird these mods gained me 5 mph in the quarter, and allowed me to run 89 octane at 10 lbs boost

 

[zelone]

Thanks for the great tips.

Crashcraft,
I do have the coolant lines through the throttle body bypassed. The other ideas for coating the intake, etc, are very interesting. I will be doing alot of research to find ways to keep the boosted air cool.

 

[wildcatgeorge]

That is the problem, boosted air is not cool, the compressing process can make boost
air 300F in some cases, your problem is not heat transfer from the engine, but cooling
the boosted air before it enters the cylinders.

Some aftercoolers of heavy trucks use the engine coolant to cool boost air,
and the coolant temps are often 200-210F, so even lowering the boost air to
215-230F has a benefit for improved power, the best solution is a air to air
intercooler, overall it will provide the most cooling of the boost charge, a water
to air cooler will have a smaller "footprint" over a air to air, and with a seperate radiator for the cooling medium, will provide a more even air temp drop of the
boost air

 

[drjclark]

I am presently constructing a CO2 cooled intercooler for my blown BMW 530i. The CO2 would be sprayed into the intercooler (which would have a housing like an air/water design), at WOT. This hopefully would reduce temps without the concerns of plumbing, pumps, hoses, ....

An outlet in the housing would be of such a size as not to allow high pressures to develope, but rather "trap" the gas long enough to allow heat transfer to occur.

What do you guys think?

 

[wildcatgeorge]

I would like to see some test data, my thoughts
are that to get the cooling you seek it would
require a high volume of CO2 to be sprayed
in a pattern that would blanket the surface of the
intercooler, and then it needs to be drawn through
the fins to the other side to provide even cooling.

The problem I forsee would be the CO2 tank freezing
up along, with the supply lines, and you don't want any
regulators freezing up or you now have a 1500 PSI
sub zero liquid gas and no pressure control I.E. Bomb
in your boot, (for you English Gents).

I don't want to say it will not work, the idea is a good
one and has merit, I just wonder if the work is worth
the effect. I run a large intercooler, air to air, and the
cooled air is cold heading for the motor on a cold day,
so I get plenty of cooling effect. I do however get a
much smaller drop when it's 100F outside, still well
below the 300F coming from the turbo.

One important factor, is your BMW a racecar?
and if it is, do you do long track or drags?
A short run like a drag race would tollerate
a CO2 cooled exchanger, without the nasty
side effects of the freezing lines. Track or
street use I fear would not fair so well, I
think here that application is the key to
success.

Good Luck,
Darrin

 

[Proxses]

Well, I just joined the forums.
One thing you could do is place a small intercooler between the blower discharge port and the discharge manifold that leads to the lower intake. Now, the problem with doing this is that you will lower the resting position of the blower and alter the belt geometry. This may produce belt slippage and the blower may even sit on the valve covers. To get around this what you can do is get a phenolic spacer. They come in 3/8 and 1 inch thicknesses. The spacer goes between the discharge manifold and the factory lower manifold.
So with the spacer in place, and by placing a small intercooler at the discharge port, what you are effectively doing is moving the discharge manifold up 3/8 to 1 inch, adding the needed intercooler, and allowing the blower to remain in the position it was designed for.

Now the intercooler you would have to place above the discharge port would have to be an air to water unit.
What do you think?

 

[zelone]

Proxses,
The idea of an intercooler at the blower outlet is a great one, but it is easier said then done. I have heard of people raising the blower up with a 3/8" spacer, but I think any more then that will be too high, and affect belt geometry, hood clearance, etc. I have also heard some people talk of blocking off the discharge manifold, and cutting 2 holes, one before the block off, one after. Then running pipes to a A/A intercooler mounted in the cowl area. It would be a tight fit, if at all possible to get the pipes from the outlet to fit with a reasonable sized hood. I might try the water injection, there has been alot of good results lately with it.
Thanks everyone!

 

[drjclark]

Darrin,
Could copper tubing be plumbed to spray into each row of fins? Also, how long of a duration of CO2 spray would cause freezing? I use WOT maybe 7-10 sec. max.(daily driver, sometimes tracked) Could underhood temps keep the lines warm enough for short blasts?

My whole problem is space. If I have enough room after it is fabricated, I will switch to the A/W setup. I have an A/A intercooler that I could run water through as a heat exchanger, and a shurflo 16 gal/min. pump. It is about 3 times larger in volume than the A/W intercooler. I did fabricate an A/A setup but the tubing route was so long the ECU had trouble adjusting and it ran like crap. The other option would have been to place the MAF sensor after the compressor, but the effects of the heat and oil vapor concerned me. But if it were cooled by the intercooler, it would not be so hot then, uh?

Anyway, I love to tinker, and will eventually come up with something. I have to be disciplined enough to resist increasing boost however, my compression ratio is 10:1!

TIA,
Jack

 

[wildcatgeorge]

10:1 is not ideal for a boosted engine.
7:1 or 7.5:1 is much better, not that it cannot
be done, you just get better overall effect with
lower CR.

The problem is not the lines freezing, it will be the tank
and regulator, and if no regulator the electric selonoid
that controls the flow. A 10 or even 30 second WOT
condition should not cause freezing, but warm lines
carry warm CO2 gas, and will not cool the intake charge.

Most likely you will have to shoot liquid/vapor CO2 through
the lines to spray onto the heat exchanger, and yes you can
fab some copper lines to spray the CO2 inside the enclosure,
tho under that low temp and high pressure, steel lines might be
better, and use 3/8" lines to help prevent dry ice from forming
and clogging the line.

You might want to consider water/alcohol injection to reduce
pinging and cool the charge too. Even with cold intake air 10:1
will start to ping on pump gas, and unless you are willing to pay
the price for unleaded racing gas, I would do a water injection
system too. The alcohol adds some RON to the fuel charge as well
as more fuel to avoid a lean condition, as well as it evoporates
quickly which helps to cool the charge. The water also evaporates
but at a slower rate, and slows the combustion in the chamber
which reduces the tendency to knock under WOT.

Your MAF should be just before the compressor, compressed air
is more dense so you will not get the true air flow. that must have
been a long intercooler route to effect your performance. I have
seen 5 or 6 feet routes and it has not effected the performance.

My route is about 5 feet plus intercooler, which is 23x17" 2 core
rows, (volvo) and performance\throttle responce is fine, I also
run a MAP or speed density system which measures the manifold
PSI\vacuum instantly. Have you considered the MegaSquirt EFI ECU?
it might give you what your looking for, altho it is not a smog legal
system, tuned right it should be hard to detect in a visual inspection.

I'm working on a MS system now to put into my project toy.
my challenge is that I never had a MPI fuel injection system to
work with so I have to fab my own system from donor parts.

I fabed my own exhaust header, why not intake manifold?

OK now you have to get after it and send us some pics, or a site
with your pics on it! Good Luck
Darrin

 

[drjclark]

My BMW is a 2001 530i. The ECU is factory, but reprogrammed by ESS in Norway, of all places. I installed the Aquamist 2d system which injects water in proportion to the fuel injectors. 2 pressurized accumulators are used to maintain pressure until the electromagnetic pump kicks in.Intake temp drops from from about 170 to 110'F at WOT. The knock sensor in the ECU however retards timing and dumps fuel to also cool the CC and reduce pre-detonation. I think they made the maps pretty conservative for a mass produced product: less liability = less fun for me.

What would be your opinion in regards to the best place to locate a CO2 bottle. Naturally, I would insulate the hoses to help limit heat soak.

I have also looked at the potential of using thermoelectrics to build a water chiller; either to cool the H2O/Alacohol mix, or the water for an A/W intercooler. Or, to be incorporated into the intercooler some way.

Don't know if they provide the needed temps at the duration thereof to chill the amount of water I need to use, or the amount of air pumped by the compressor. Must experiment. I have even toyed with the idea of using a refridgerated air dryer and resevoir to chill water, but its weight is detrimental. I guess I could put less gas in the car. Is is AC powered and the converter I bound can't pull it off. I have researched some converters that will. Maybe an extra battery would help. Dang! did I say I also wanted to do this on the cheap!

I will post a link shortly to pics. Do you have a broadband connection?
Thanks for the info!
Jack