Exhaust cooling?

[Nicator]

I apologize in advance if this has been touched on previously.

I am contemplating a 'cryogenic' CO2 system for an N/A vehicle. The CO2, by some artifice, will be used in the induction tract to cool the air charge (naturally, it will not be allowed to be ingested by the engine).

The CO2 has to vent somewhere, and since this is an N/A application, a traditional intercooler halo doesn't apply.

Rather than just dump the CO2 any old place, I'd like to put it to (potentially) good use.

Knowing that racers have, for years, placed the tailpipe of the exhaust in a low-pressure area to facilitate improved exhaust flow, I am wondering if there might be some way to vent the CO2 in such a way as to improve exhaust flow.

What do you think the possibilities are?

Thank you for considering this topic this far!

 

[MikeHalloran]

The CO2 has to exit the intake cooler at a pressure above atmospheric, so nothing would be gained by venting the exhaust into that space.

Perhaps you were thinking of exhausting the CO2 at high pressure, through an eductor that would scavenge exhaust gas. You would need to dump a lot of CO2 to do that, and there would be a weight penalty for carrying it in the first place.

It doesn't sound like a super winner of an idea. Sorry.



Mike Halloran
Pembroke Pines, FL, USA

 

[JimCasey]

I'm sitting here unable to decide what N/A stands for.

Venting the CO2 into a subamospheric area to reduce lift is one idea. Front of the hood is one place. Base of the windshield is high pressure. Back window area is low. The sides of the vehicle tend to have lower pressure than the rear....that's why exhaust gas comes in the rear of a hatchback if the side windows are down-but venting out the sides won't kill lift.

Since this is apparently a prototype vehicle, flooding the engine bay with spent CO2 as a flame inhibitor might be prudent, too.

 

[Nicator]

N/A is just a 'normally' or 'naturally' aspirated vehicle. Non-turbo or supercharged.

I wasn't so much thinking of the pressurization of the CO2 scavenging exhaust...I was thinking of its low temperature doing so. Though it will have picked up heat from the intake charge, it will still be a mite cooler than exhaust.

It was an iffy idea to begin with; no offense taken...but you can't fault me for wanting to avoid wasting the CO2...

 

[Lou Scannon]

I question the value of using CO2 in the first place(cryogenic or compressed) for cooling the intake charge of a vehicular engine. My engineering instinct tells me that in comparison to more common methods of increasing power, the CO2 approach will add more weight and cost more per hp added. Have you done any analysis to show the power benefit for a given rate of CO2 use?

 

[globi5]

Air density is roughly proportional to 1/temperature (abolute). So there's something to be gained especially if you were to increase the compression ratio at the same time.

As far as the remaining CO2 goes:
When liquid CO2 is heated by the intake charge its vapor pressure will rise. If you release CO2 into the exhaust gas after enough pressure has been built up (and taking more heat of the intake during evaporation of CO2), its quick release into the exhaust stream will possibly act as a jet pump (if designed accordingly) and reduce pressure in the exhaust for a very short time. But even if successful reducing pressure in the exhaust doesn't really affect power significantly.

 

[globi5]

Or you could release the CO2 gas onto a Turbonique supercharger (which has been discussed earlier in an other thread) and possibly generate some extra boost for a few seconds.

 

[Lou Scannon]

globi5, I fully understand there is a benefit from cooling the charge. What I was asking is for the quantification of this benefit as a function of the rate of CO2 use. I suspect that this analysis will show that the cost and added weight of CO2 & delivery equipment per added hp wiil be much higher than for other common means of increasing power.

 

[globi5]

It depends for how much time you intend to use it. If it is only required for a 1/4 mile, my guess would be, that power to weight ratio of the vehicle will be increased.

 

[Nicator]

Cryogenic systems are marketed and packaged much like nitrous oxide systems. The difference being that the CO2 is used to cool the intake, fuel rail, and perhaps an intercooler by various appliances. Otherwise, in comes in a similar bottle and trimmings. The system is setup to be activated, and triggered by a WOT switch, or window RPM type switch.

Merchants claim 1% increase in HP on an N/A vehicle. For whatever (little) its worth.

 

[patprimmer]

Cooling fuel is useless for reasons discussed in great detail in previous threads.

Cooling inlet charge is very useful to a point. The point where it stops being useful is the point where fuel evaporation problems offset charge density increases.

A manifold is a very poor heat exchanger, so just spraying CO2 on the outside of your manifold will only have a minimal effect.

A proper water to air intercooler with CO2 blowing through the water passages will work. It is not my area of expertise, so this is a bit of a SWAG, but I expect a shrouded air to air intercooler with CO2 blown into the shroud might work better as it was designed for gas to gas heat transfer and this might be reflected in the relative surface areas and fluid flow channel sizes.

Regards

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[Deltona]

Why on earth would you want to cool you exhaust gasses?

 

[Nicator]

Patprimmer, this is the media I was thinking of applying the CO2 to:

http://www.lindseyracing.com/Merchant2/merchant.mvc?Screen=CTGY&Store_Code=HP&Category_Code=THPWELD

(Though, I'm concerned as to how the extrusions might impede overall flow)

Or the barrel intercoolers found here:

http://absoluteradiator.com/intercoolers.asp

 

[JimCasey]

If you sprayed liquid CO2 (-110F saturation) onto a HX (intercooler) with atmospheric air flowing thru on the other side, in a few minutes the Air passages would be full of frost. This would negate any theoretical advantages of increased air density,

 

[crashforce]

As a shoot off from the original thread, would it be possible to have ports like waterways/ or original waterways around the inlet ports on the head connected to a co2 system to supercool the inlet and or the block for a short time?
id be worried about the sudden heat changes causing engine damage and fractures if it was injected into a hot engine for to long but it could provide big improvements in short sprints and drag racing?!?

Any thoughts?

 

[crashforce]

nicator- that pipeing from lindsay racing could work the other way round, ramming air through the inside of the pipe to cool engine coolant, could be a good way to flow some of the stagnant air from under the hood to the rear of the car aswell especially with a rear rad setup

 

[Fabrico]

Cooling intake air on a N/A engine does little more than cooling the fuel. The difference in accomplishing the two is huge. A 1% gain in HP is hardly worth carrying a CO2 bottle and related equipment around. Attempting to cool the exhaust with C02 only adds to the weight penalty.

 

[patprimmer]

Effectively cooling inlet charge or more so, the avoidance of heating it can have a noticeable power increase, however just cooling the inlet port in the head will transfer so little heat from the inlet charge that the result will be to small to measure. The cost in time, $ and weight will greatly outweigh any benefit.

As I inferred earlier, once temperatures get well below ambient, fuel evaporation problems (similar to cold start) will eat up any gains from increased charge density and even decrease power due to misfires or poor combustion.

Like everything in engine design and tuning, it is a compromise between conflicting parameters. Normal fuel is formulated to work well at the ambient temperatures in the region and season it is sold, so large deviations from those temperatures will result in poor ignition or vapour lock.

Regards

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