Dry Ice in Intake?

[cfg83]

superchow -

From what I've read, no one seems to think that there will be harm to the engine.

Aside from all the other caveats, it sounds like you could at least do a test. Leave the car parked in neutral and let it idle while the dry ice is off-gassing into the intake. This wouldn't be a complete test, but you could at least see if the engine bogs down under a controlled/safe idle/min-load condition. You could also press the accelerator and see if it runs "normally" at different RPMs. If you don't like what you see or hear, just turn the engine off and pull out the dry ice.

I don't blame you for thinking in terms of non-invasive mods. I'm a proponent of the "reversible mod", and the politics of sharing one car can be verrry complicated.

CarloSW2

[PaleMelanesian]

What about using a compressed CO2 canister instead? Same gas, but better control. You could even put a nice valve on it to regulate the output.

[instarx]

Hmmmm, the effect of CO2 in the intake is a more complex a problem than it seems at first glance. I don't think it is a given that it would cause the engine to burn leaner at all. The CO2 might make the engine run richer. The extra oxygen detected in the exhaust by the oxygen sensor might make the engine management system think there was insufficient fuel for complete combustion, causing it to richen the mixture.

Second, CO2 is a major greenhouse gas. So as well as using more fuel to drive the same distance you would be adding even more greenhouse gases to the environment from the dry ice.

Third, it takes a lot of energy (electricity) to make dry ice. That puts even more pollutants, including more greenhouse gases, into the air from the generating plant.

Adding CO2, in the form of dry ice OR compressed CO2 seems like a bad idea on several levels, in my opinion.

[pasadena_commut]

Originally Posted by superchow

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?

If you want to fool the ECU, lie to it directly. Unplug the oxygen sensors, plug them into some circuit/computer, and have that "black box" tell the ECU whatever you want it to see. For instance, if you want to lean things out a few percent have the box tell the ECU there is less oxygen in the exhaust than is actually present. If you don't push it too far you may be able to force the engine to run a bit leaner. Push it too far and the car won't run very well. I don't know exactly how the ECU reads the oxygen sensors (measures voltage, resistance, capacitance, whatever), so you would need to do some research to figure out how to make a controllable "fake" oxygen sensor for the ECU to read.

Don't expect to pass an emission inspection with this in place though!

[hummingbird]

Superchow,

You would be a good scientist, I am not sure about you making a good engineer

Your answers are summed up by roflwaffle and jamesqf. Christ has taken care of demolishing the practicality.

A leaner mixture would be already equivalent to one having CO2 filler. If there is insufficient fuel to burn all of oxygen in the mixture, it does not matter if it is O2 or CO2, it (non-fuel part/excess O2/air) won't burn. Also as jamesqf pointed out, gaming/fooling the ECU is done best through modding ECU sw /instrumentation.

I don't have an answer to the cooling brought by the dry ice, but somebody else more qualified should answer (and let me just meddle with interpretation of others' post but what the heck, are not newbies allowed this to add to their post count? )

Cheers,
hummingbird

[jamesqf]

Originally Posted by PaleMelanesian

What about using a compressed CO2 canister instead?

These should be fairly easy to find, too, since they're commonly used as fire extinguishers (preferred for electrical fires, IIRC). Which I think says something about the practicality of the original idea :-)

[Christ]

Originally Posted by instarx

Hmmmm, the effect of CO2 in the intake is a more complex a problem than it seems at first glance. I don't think it is a given that it would cause the engine to burn leaner at all. The CO2 might make the engine run richer. The extra oxygen detected in the exhaust by the oxygen sensor might make the engine management system think there was insufficient fuel for complete combustion, causing it to richen the mixture.

Second, CO2 is a major greenhouse gas. So as well as using more fuel to drive the same distance you would be adding even more greenhouse gases to the environment from the dry ice.

Third, it takes a lot of energy (electricity) to make dry ice. That puts even more pollutants, including more greenhouse gases, into the air from the generating plant.

Adding CO2, in the form of dry ice OR compressed CO2 seems like a bad idea on several levels, in my opinion.

instarx - there is an emissions trick to this - You're leaning the engine out, which creates higher NOx gas emissions, and adding CO2 to the mix actually will clean the NOx via the catalytic convertor.

BTW - the O2 sensor will not mistake CO2 for O2, it's a different compound, that creates a different signal. The O2 sensor is trained to see a certain amount of O2 after a burn cycle (little or none is preferred), so you're giving the O2 sensor exactly what it wants, by displacing oxygen intake. It will read that there is substantially less air than the "normal" volume, and start pulling fuel until it gets a bottom line.

OP - you may still run rich - the ECU can only pull an amount of fuel that would cause your engine "normally" to go too lean to recover. It's a failsafe feature that prevents unmodified engines from leaning out far enough to actually kill themselves. This is also why no racer (normally) uses OEM software. They modify the fuel curves, usually stating something like "pig rich" in the interim.

I wasn't trying to say for sure that you couldn't do it, I was explaining exactly what was more than likely to happen. With no direct way to meter when or how much of your CO2 enters the air stream, you've ended up with an uncontrollable cycle. This is not conducive to good testing procedures.

Ideally, to pull this off, you'd have to meter it so that all of your CO2 gas enters the cylinder in a pulse, BEFORE any air/fuel goes in, so you can keep ideal combustion in the cylinder. (The air/fuel mix would end up stacked on top of the CO2). You can give it a shot, in that resonator box, but I don't think you're going to see much of anything happening, and if you do, you're going to see damage to your engine from leaning out the fuel mix due to a lack of *dynamic compression*.

Everyone - If I understand correctly, and I think I do - He's not really looking to lean the air/fuel mix, more-so, he's trying to lower the amount of fuel used by limiting the amount of combustion space it has to work in. Think Atkinson cycle. Adding CO2 limits the amount of combustion space he has, which technically limits the usable displacement of the engine... bad terminology owns this thread, in that he's not trying to lean it out at all.. he'll still be running close to stoich, for the amount of usable air volume he has in the combustion chamber (if the ECU can compensate that far, if it can't, he'll be running rich, as instarx suggested, b/c of too little air, and the ECU not being able to trim fuel enough to compensate.)

[pasadena_commut]

Originally Posted by instarx

Second, CO2 is a major greenhouse gas. So as well as using more fuel to drive the same distance you would be adding even more greenhouse gases to the environment from the dry ice.

Nitrogen could be used instead.

Carrying around this much inert gas in any form is likely to be a problem.

Let's get a rough idea of how much volume one would need. Assume a 2.0 L engine. If the car's average RPM is 2000, and there is one intake cycle every other rotation (4 stroke engine), then the motor will suck in 2000 L per minute. Assume the maximum perturbation is replacing 10% of that with the inert gas, which would be 200 L per minute. A scuba tank (80 cu ft at 3000 psi) is equivalent to (2265 L at 3000 (PSI)/14.7 (PSI/ATM) = 204 atm) so at 1 atm that would be 2265*204 L = 462060 L. At 200 L per minute this method could run for 2310 minutes, or 38.5 hours. In other words, it is within the realm of engineering feasibility to inject this much inert gas under more or less normal driving conditions.

Does it make sense to do so? That depends on how much energy it takes to load that scuba tank with nitrogen, and how much energy is wasted carrying around the extra weight. One also has to consider the lowered intake temperature which would result from expanding the compressed gas, although by routing the nitrogen line alongside the exhaust manifold it is probably possible to compensate pretty well for that effect.

[blueflame]

What about ducting the air intake from somewhere cooler?

I'm wondering what drawing the cool air from in front of the air con outlet would do for engine power/and FE in hot weather. Be noisy in the cab, like an angry vacuum cleaner.

Tar seal is melting here in NZ yesterday and today its a hot one too. The road and tyres make a ripping sound as you go through the soft stuff. From a FE perspective the rolling resistance is high, and it pays to drive outside of the grooves made by other vehicles.

I've noticed when my engine is cooler from driving in the shaded forest or descending a mountain that I have way more power than when the motor is really hot like after climbing a mountain.

I'm getting the best FE now though, 75mpg US average tanks on mountainous roads with a lot of braking and tons of engine off time...I travel for 6 minutes without having to turn on!

[Lazarus]

Originally Posted by blueflame

What about ducting the air intake from somewhere cooler?

I'm wondering what drawing the cool air from in front of the air con outlet would do for engine power/and FE in hot weather. Be noisy in the cab, like an angry vacuum cleaner.

Tar seal is melting here in NZ yesterday and today its a hot one too. The road and tyres make a ripping sound as you go through the soft stuff. From a FE perspective the rolling resistance is high, and it pays to drive outside of the grooves made by other vehicles.

I've noticed when my engine is cooler from driving in the shaded forest or descending a mountain that I have way more power than when the motor is really hot like after climbing a mountain.

I'm getting the best FE now though, 75mpg US average tanks on mountainous roads with a lot of braking and tons of engine off time...I travel for 6 minutes without having to turn on!

Some cars do better with a high IAT like the Saturn. Mine did not. When the IAT got over about 110 it started to retard the timing and the FE would decrease. We get temps high 90-100+ and my IAT would reach temps of 130-140 or more. My high tech solution was to put a wet sponge in the bottom of the air box. This cooled the temps to my optimum temps and lasted for the hour commute.