Dry Ice in Intake?

[superchow]

Well hello everybody, and Happy New (EM) Year!

I was thinking about water injection as a means to cure my 07 Civic's lackluster response in hot weather (a whole other story), when I contemplated means to improve gas mileage under light loads.

Can anybody think of any reason why dropping some cubes of dry ice (frozen CO2, no?) into the intake would not trick the ECU to interpret that as a low oxygen environment and reduce the fuel injection rate? My theory is that the dry ice when returning into gaseous CO2 would mix with the air rushing past it. The air/CO2 mix should have less oxygen in it and to keep the fuel/air mix right, the engine would have to reduce the amount of fuel injected, therefore causing a lean burn, right?

Think: Nitrous injection - but the opposite!

Maybe it would choke out the engine completely? Could this hurt the engine? Thanks for the feedback!

[cfg83]

superchow -

Originally Posted by superchow

Well hello everybody, and Happy New (EM) Year!

I was thinking about water injection as a means to cure my 07 Civic's lackluster response in hot weather (a whole other story), when I contemplated means to improve gas mileage under light loads.

Can anybody think of any reason why dropping some cubes of dry ice (frozen CO2, no?) into the intake would not trick the ECU to interpret that as a low oxygen environment and reduce the fuel injection rate? My theory is that the dry ice when returning into gaseous CO2 would mix with the air rushing past it. The air/CO2 mix should have less oxygen in it and to keep the fuel/air mix right, the engine would have to reduce the amount of fuel injected, therefore causing a lean burn, right?

Think: Nitrous injection - but the opposite!

Maybe it would choke out the engine completely? Could this hurt the engine? Thanks for the feedback!

I don't know, but I am *guessing* it would richen the fuel mixture on the assumption that the combustion will free the 02 in the C02 from the dry ice. I say this because the 02 sensor in the exhaust manifold would then measure an increase in oxygen levels, creating a "lean burn" reading. The car's ECU/PCM would then increase the amount of fuel injected to bring you back to stoichiometric AFR of 14.7:1.

I don't think it would hurt the engine because EGR already recirculates C02 into the combustion chamber (at much higher temperatures than dry ice CO2).

What are the "leftovers" after the dry ice has melted away? Water? Goop?

But someone who really knows pipe up.

CarloSW2

[robbiewt]

Is there a chance that the extra CO2 could prevent combustion?

[aerohead]

I believe the outcome would in effect,be like lowering the displacement of the engine,with loss of power,efficiency,mpg,with all the original canibalistic internal losses.------------- The CO2 is already fully oxidized,will act as an inert gas,displacing valuable oxygen,reduce the charge density,lower BSFC.----------------- Beside all that,how could you possibly hope to monitor and adjust" stoiciometric" ratios.---------------- Co2 is used in fire extinguishers,and plenty believe we already have plenty in the atmosphere.-------------------------- I think you should look elsewhere for a solution to driveability issues.

[superchow]

Originally Posted by aerohead

I believe the outcome would in effect,be like lowering the displacement of the engine,with loss of power,efficiency,mpg,with all the original canibalistic internal losses.------------- The CO2 is already fully oxidized,will act as an inert gas,displacing valuable oxygen,reduce the charge density,lower BSFC.----------------- Beside all that,how could you possibly hope to monitor and adjust" stoiciometric" ratios.---------------- Co2 is used in fire extinguishers,and plenty believe we already have plenty in the atmosphere.-------------------------- I think you should look elsewhere for a solution to driveability issues.

aerohead - I read as much as I could find about the R18A engine in the Civic and one of its highly touted points is the low friction coatings in the engine block cylinders. I notice this every day when engine braking: It just does not want to slow down as much as other cars that I've driven. Yes, the engine would become less efficient. Even so I hypothesize that despite the negative effect of the oxygen being replaced by CO2 and thus reducing engine power and efficiency, the overall amount of fuel being injected would be lower than at with plain air.

Stoichiometric ratios - Less oxygen should mean less fuel, no? I'm proposing more "filler" to be pumped and less stuff that could react with gasoline. Where's a chemist when you need one!

Yes, using CO2 would be counterintuitive for ecological reasons... Any ideas for frozen inert gasses that could function as a substitute for dry ice?

[poindexter]

Originally Posted by cfg83

superchow -

What are the "leftovers" after the dry ice has melted away? Water? Goop?

But someone who really knows pipe up.

CarloSW2

Nothing would be left over. Dry ice is just frozen CO2, once it sublimates it is gone with the wind.

Originally Posted by cfg83

Yes, using CO2 would be counterintuitive for ecological reasons... Any ideas for frozen inert gasses that could function as a substitute for dry ice?

Even if it did help, consider that it takes a lot of energy to make, store, and distribute dry ice or to freeze any other compound.

[roflwaffle]

Your EGR system already does this by keeping or rerouting exhaust (mostly CO2) back into the cylinder. The problem is that at low loads too much CO2 results in misfires for most vehicles, which results in other emissions spikes. The newer GDI engines allow for precise control of the incoming fuel mixture, which lets manufacturers run more EGR and relatively lean A:F ratios in order to improve BSFC w/o increasing emissions. Here's some more info.

[jamesqf]

You might want to re-think this one :-) How much does dry ice cost (not just money, but in energy) vs the amount of gas you expect to save? How long will the dry ice last in the summer? How much extra gas will you burn driving to wherever you plan to get the dry ice? How often will you have to stop and add a chunk or two to the air intake?

If all you want is to fool the ECU, why not just put a small microprocessor in the circuit between it and the sensor(s), and map whatever response you want?

Really, you should have waited until April 1st to post this one :-)

[Christ]

james - the resistor thing would cause it to lean out, but it wouldn't add "filler" to the combustion process... that's his point - if you add CO2, it displaces X volume that now cannot be filled by air/fuel.

His idea is bascially water injection with CO2 instead.

Here's the problem - aside from cost, which has fervently been pointed out already, the rate at which the CO2 sublimates would increase with ambient temperature... it would nearly be impossible (given your theoretical setup) to keep track of how much CO2 you're adding to the combustion process, and you may even add enough of it that there wouldn't be enough room left for the air and fuel to create a strong enough combustion process to actually keep the engine running. Chances are, after the engine warmed up, you'd starve it, and it would shut off.

Another issue with doing this - you're making the air/fuel mix very sparse in such a large area, which makes it harder to ignite... ideally, you want a richer mixture nearer the spark plug, and a leaner mixture everywhere else, or at least a homogenous mixture everywhere.

Adding random (or even controlled) amounts of CO2 to the mix, if you add enough, will make it so that parts of the a/f mixture are all over the place. You'd have to control the timing for the gaseous CO2 to be injected, so that it would limit access to the areas closer to the piston, and air/fuel could be drawn in on top of it... what you'd have essentially done is lowered the effective stroke of your engine, more accurately, lowered the displacement... there are easier, cheaper, more reliable ways to do this.

[superchow]

Granted, the overall cost of energy involved in this setup would be prohibitive. But, I must mention that the Civic has a resonance chamber plumbed before the air filter almost in front of the front left wheel well. I am guessing that there would be about 2-3 feet of air intake (I haven't measured, sorry). Air enters right behind the driver side headlight, drops down below the battery, to the resonance chamber, then back up to the side of the engine where the air filter is located.

Theoretically dropping a couple of cubes of dry ice into the air intake would get stuck in the resonance chamber and not really close to anything hot.

I have never played around with dry ice, and I do not know how quickly it sublimates, but surely it could last long enough to drive a few hundred miles? Long enough for a personal record breaking run?

I have the feeling like this idea will not take off until I go from theory to practice.

I do not have an idea if this would be even financially viable - probably not! - but after seeing racing cars using dry ice to cool off the air to their radiators before the air passes through the radiator, something must have been planted in my mind.

Oh, and for everyone asking "why?": I am very shy of actually chopping around on my vehicle because a) it is relatively new, and b) it is the only vehicle in our household and my wife would not appreciate walking to work in the pacific NW rainy winters. Therefore I am limited to non-invasive mods - if there is such a thing.

Thanks for the feedback entertaining my wacky ideas. If not here, then where, right?