[Isaac Zachary]

I have no idea if this would ever work nor can I seem to find anyone else that's even so much as thought of the idea, much less tried it.

Why
I think I'll explain the why first. If you can take all the nitrogen out of the intake charge and replace it with carbon dioxide but still have it mixed with about 20% oxygen then the formation of nitrogen oxides should be theoretically eliminated. With no NOx then you can run as lean as you want, beneficial to both diesel and gasoline engine efficiencies. You also can run as high of a combustion temperature as the engine and fuel can handle, which can also increase efficiency.

A side benefit is that we will be getting free water with this system which could be used for water injection, perhaps so that you could run higher compression ratios without detonation or so that you could run stoichiometric AFR's at high load.

A possible side benefit is that there would be the possibility of running higher concentrations of oxygen than 20%. I'm not sure if that would be practical, but from a theoretical standpoint ICE's should be more efficient with higher concentrations of oxygen since the combustion temperatures would be higher.

To sum it up, theoretically you should get an ultra-low emissions engine that has the potential of getting better fuel mileage.

How it's supposed to work
Take an engine and loop the exhaust through a cooler and right back into the intake. Then take a high purity oxygen generator (probably of the Vacuum Pressure Swing Adsorption variety) and fit that on the vehicle somehow and feed the oxygen into the intake. We may also want to prefill the exhaust/intake loop with CO2 before starting just to remove any nitrogen from the system.

How this theoretical engine works is that we start off with CO2 and some water vapor in the system headed towards the intake. The oxygen generator separates the NOx out of the air and introduces the O2 into that CO2 in the intake. Fuel is added any way seen fit (port injection, TBI, carburetor, direct injection, etc.).

During the combustion process we should get about everything we normally get emissionswise except NOx. Since the engine can run leaner with no emissions dependency for EGR we should get less CO, HC and PM emissions even on diesels. Not only that, but a lot of the exhaust (75-80%?) will be cooled and funneled right back into the engine to give it another chance to burn. The remaining exhaust can be run through a catalytic converter that should have an easy time burning up anything left over for a super-ultra-very-very-low emissions ICE. The catalytic converter could also be made much cheaper or perhaps even eliminated all together and still achieve these ultra-low emissions.

Of course cooling the exhaust means we'll get a lot of liquid water which may be used in water injection. Since water has an octane effect this could lead to some very high compression rations.

Problems
Well of course cost is a major one. Complexity another.

There's also the question of how efficient the oxygen concentrator will need to be since there exists the potential for it to sap way too much power from the engine just to provide enough oxygen to run. Whether or not the efficiency benefits from not having to deal with NOx emissions would be enough to overcome the power needed to run the oxygen generator would be key to whether this would make for better fuel mileage or not.

Also it will need a lot more cooling since we'll have to be cooling a large amount of the exhaust back down to near ambient. Which also means there can be the problem of not being able to cool the exhaust enough which could cause detonation problems. We could could try to compensate by holding back on the amount of oxygen being used but that would defeat the purpose of this setup.

Possible application
Since the oxygen generator will take up a lot of space this might work best on a very small engine so that the oxygen generator can be made as small as possible too. I'm thinking that this might be good as a range-extending engine on a BEVx type vehicle, or at least some sort of hybrid that has enough umph! from the electric (or hydraulic) drive train so that the engine can be made quite small.

Thanks!
Anyhow, thanks for reading my crazy idea.