Quote:
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.
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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.)