Lean Burn without Purge Cycles

[IamIan]

A few more options I found on the side of other ( non ICE purge ) ways of dealing with the NOx.

ICE-PURGE
The OEM CAT uses chemical energy of unburned hydrocarbons from a ICE purge event in order to chemically reduce the NOx with the catalyst in the catalytic converter.

CAT-PURGE
The Link in the OP was about an alternative of directly injecting those unburned hydrocarbons (fuel) into the CAT itself ... allow the ICE to stay lean ... and just the CAT does a purge event.

ELECTRO-CHEMICAL
Another option is if the catalyst in the catalytic converter was a electro-chemical one instead of a chemical-chemical one ... so the energy needed to break down the NOx can come from electricity instead of fuel ... a PHEV would not have to use gasoline to provide the electricity for the electro-chemical reaction.

PHOTO-CHEMICAL
Another Option similar to the electro-chemical is to use light energy as the source to break down the NOx... although I suspect it would be much more difficult / less efficient in application.

[IamIan]

Another Thought ...

Short Version:
I think it is reasonable to think there is room for significant improvement in the OEM system , in regards to how much it takes from the ICE for those NOx Purge events.

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Long Version:

At standard pressure and temperature it takes about:
~181kj to take 2NO to N2+O2
~113kj to take 2NO2 to 2NO+O2

Worst case is 2 moles of NO2 ... it would take about ~294kj of energy ... ( ~82Wh ) ... in practice , more because of being less than 100% efficient.

More at higher temperature ( like those in the exhaust ) because the higher the temperature above standard the greater the natural tendency to go from N2+O2 to 2NO ... or from 2NO+O2 to 2NO2.

A larger % of NOx is produced in Lean Burn engine operation.

The OEM system gets his energy as chemical energy from unburned hydrocarbons of fuel during a ICE purge event.

2 moles of NO2 = 72g.

So due to devices being less than 100% efficient we know the NOx system needs more than ~1.14 Wh/g of NOx.

Although exactly how much more will be a function of how efficient the NOx system is ... Prior to ~1975 when the NOx systems began to become standard in the U.S. I've seen figures estimating NOx levels at an average of ~4g/mile from the average fleet getting ~15 MPG at that time ... or about ~60g/Gal of the fuel burned became NOx.

The OEM Gen-1 Insight system is rated for an average of ~53MPG producing ~0.3g/mile NOx ... or about ~15.9g/Gal of the fuel burned becomes NOx... which is a significant improvement as far as NOx goes.

That is a reduction of about ~44.1g/Gal ... even at 100% efficiency it would take more than about ~50wh of energy to do that ... given about ~36kwh of energy content per gallon of gasoline ... ~50wh is only about ~0.14% of the fuel's energy content.

We know in practice it will be more than this due to higher than standard temperatures in the exhaust and due to less than 100% efficient conversions and devices.

But those purge cycles definitely reduce ICE efficiency by far more than ~0.14%... a lot more... therefore it seems to me that there should be significant room for efficiency improvement in the system... I have no doubt the OEM design was also a bit of a compromise in temperatures of operating conditions , cost, etc ... If the NOx system was even just ~14% energy efficient it would only consume about ~1% of the fuels' energy content to get the same NOx reductions ... much less than the current ICE purge event system does.

[nasphere]

Has anyone looked into the evap system purge? Does it have any ties to the lean burn oriented purge? Someone with peter's OBD2C&C could monitor the evap duty cycle during lean burn and during a purge cycle to verify.

[Eli]

I'm going to look for this as well, but Peter reported that upon entering a purge, the AFR goes to ~13.9:1 for a moment and then to 14.5:1. This makes perfect sense - essentially injects unburned hydrocarbons into the cat by richening the mixture.

Someone should devise a fuel injected cat and see what happens, it would be quite interesting. The amount of fuel needed would be trivially small, I think. I bet fuel injectors get pretty small. Maybe a uC to monitor Lean burn and start a timer, pulsing the small fuel injector every X amount of time(30 seconds, 1 minute?). Easy, right?

[IamIan]

Originally Posted by Eli

Someone should devise a fuel injected cat and see what happens, it would be quite interesting.

Once I read about the research prototype doing that I posted in the OP ... That was something that went onto my ... unfortunately long list of projects ... Although the Electro-Chemical option is also appealing ... The idea of being able to extended LB operation cleanly is very appealing to me ... but I'm pretty slow when it comes to checking off items on my ever growing list ... So who knows when I will get to it ... more than happy if anyone else gets to any other part of it before me.

The price of a cat to toy around with ... is no small thing ... I've seen prices between $600 and $1,500 ... plus the cost of other parts ... and labor to do it all ... and of course the whole thing is mute if OEM LB behavior can't be altered which is another significant part of the project ... haven't tested it yet ... but given the known sensor error codes ... I suspect that Peter was right an altering the LB behavior will be more involved than just altering the sensors signals ... weather it is because we cleaned up the NOx ourselves or not.

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Although it might go without saying ...

Even if a few years down the road we do manage to accomplish the whole package ... LB extension and emissions ... as great as that would be ... less fuel per engine cycle also means less power per engine cycle ... as those getting into LB already know ... LB reduces the % of fuel by more than it increases efficiency ... although I haven't seen tested dyno numbers on it ... I suspect we will be reducing engine peak power by almost ~30HP ... won't mater for a lot of the time cruising down the flat open highway ... but just saying ... even if everything gets worked out ... this will be a mod for people far more interested in efficiency than power... now for me less power will be fine the majority of the time ... but there will be a few times here and there where I would still want more power than that... even if it would be a small % of the drive time , I think for me at least I would not want 100% LB 100% of the time... at least not without a slightly more powerful IMA system and a larger battery to take up more of the gaps... but that's another project.