Gas engine idea/question

[KrisZ]

So, coming back from work I was stuck in traffic today and I started thinking about modern gasoline engines. We all know that manufacturers face a constant battle between improving fuel economy and meeting more and more stringent emission laws.
That got me thinking about diesel engines and how their exhaust is treated with urea injection to reduce NOx emissions since they run so lean. I thought why not do the same and treat gasoline engine exhaust with urea. This would allow the use of lean burn once again and meet NOx emissions at the same time.

Is this something that can actually be done, or is there a good technical barrier that prevents manufacturers from doing it. What do you guys think?

 

[jrustles]

I think gasoline engines use the three-way catalyst to control NOx and HC, CO. The stoichiometric flip-flop (alternating on either side of 14.7) is due to the following:
Quote:

Three-way catalysts are effective when the engine is operated within a narrow band of air-fuel ratios near stoichiometry, such that the exhaust gas oscillates between rich (excess fuel) and lean (excess oxygen) conditions. However, conversion efficiency falls very rapidly when the engine is operated outside of that band of air-fuel ratios. Under lean engine operation, there is excess oxygen and the reduction of NOx is not favored. Under rich conditions, the excess fuel consumes all of the available oxygen prior to the catalyst, thus only stored oxygen is available for the oxidation function. Closed-loop control systems are necessary because of the conflicting requirements for effective NOx reduction and HC oxidation. The control system must prevent the NOx reduction catalyst from becoming fully oxidized, yet replenish the oxygen storage material to maintain its function as an oxidation catalyst.


NOx is aso controlled by EGR function, reducing the combustion temperature.

In traditional diesels, the combustion temperatures and pressures are unavoidably high, inevitably producing higher NOx, that EGR cannot adequately reduce.

Quote:
In 2010, most light-duty diesel manufacturers in the U.S. added catalytic systems to their vehicles to meet new federal emissions requirements. There are two techniques that have been developed for the catalytic reduction of NOx emissions under lean exhaust conditions - selective catalytic reduction (SCR) and the lean NOx trap or NOx adsorber. Instead of precious metal-containing NOx adsorbers, most manufacturers selected base-metal SCR systems that use a reagent such as ammonia to reduce the NOx into nitrogen.

 

[Tegger]

Originally Posted By: KrisZ
That got me thinking about diesel engines and how their exhaust is treated with urea injection to reduce NOx emissions since they run so lean.

That's not quite why. Diesels produce lots of NOx because their fuel is designed to do exactly what gasoline is designed NOT to do: explode all at once. That's why diesels inherently produce truckloads (ha ha) of NOx.

Gasoline engines already produce just about zero NOx with existing technology.

 

[KrisZ]

Originally Posted By: Tegger


Gasoline engines already produce just about zero NOx with existing technology.


Sure they do, but they use extra fuel to do just that. In Europe where NOx emissions are more lax, lean burn modes are used in gasoline engines all the time to greatly improve fuel economy.

What I'm talking about is to use urea injection to allow lean burn modes. Right now we have to avoid lean running conditions to keep NOx in check. That would be on top of catalytic converters that only work efficiently in a narrow temp. range as pointed out by jrustles. Urea could be used to supplement catalytic converters in situations where the temp is too high for cats to work efficiently.

 

[jrustles]

theoretically, it would work

 

[JimPghPA]

I remember reading a science magazine (though I do not recall which magazine it was, probably popular science, or popular mechanics but it could have been something else) about an experimental engine that used both gasoline and Diesel, and varied how much of each was used depending on such things as the running temperature, and load on the engine. The vehicle would have two fuel tanks, one gasoline and one Diesel. Theoretically that duel fuel engine delivers better MPG's and lower pollution.

 

[expat]

Originally Posted By: JimPghPA
I remember reading a science magazine (though I do not recall which magazine it was, probably popular science, or popular mechanics but it could have been something else) about an experimental engine that used both gasoline and Diesel, and varied how much of each was used depending on such things as the running temperature, and load on the engine. The vehicle would have two fuel tanks, one gasoline and one Diesel. Theoretically that duel fuel engine delivers better MPG's and lower pollution.


There were a number of engines (Ford made some) that ran off two tanks, one Gasoline and one Kerosene.
The engine would be started on Gas then switched to Kerosene. But I don't think that had much to do with pollution control, more that in some places Kerosene is cheap.

 

[Shannow]

There were a lot of tractors that started on petrol, then switched to less volatile fuel once there was enough heat in them...

People are looking at compression ignition petrol, and diesel ignited petrol...
https://bobistheoilguy.com/forums/threads/compression-ignition-gasoline-direct-injection.205414/

I'm half interested in diesel/petrol to get additive into (and more power from) my Nissan....diesel/propane are pretty common, diesel petrol are pretty novel, but gaining.

https://bobistheoilguy.com/forums/threads/is-this-how-to-get-polyetheramine-to-di-engines.205485/

As to the OP...I think urea would work, but Cats flow pretty well these days, and are probably more effective, and don't use two tanks (two tanks was partly what killed the Olds turbos back in the 60s, when the "rocket fuel" had to be kept up to provide anti-knock) - petrol engine drivers would jack up at another compartment to mis-fill with some product or another.

Power Stations use catalysts and Ammonia for NOx control where they can't get it with staged combustion...many ways to skin a cat (no pun intended).

 

[Tegger]

Originally Posted By: KrisZ
Urea could be used to supplement catalytic converters in situations where the temp is too high for cats to work efficiently.

If you're looking for some kind of savings by running urea, I suspect that any savings on fuel may be quickly eaten up -- or exceeded -- by the cost of the urea and its associated equipment. If urea were less costly, wouldn't the automakers be using it already?

 

[NateDN10]

Originally Posted By: JimPghPA
I remember reading a science magazine (though I do not recall which magazine it was, probably popular science, or popular mechanics but it could have been something else) about an experimental engine that used both gasoline and Diesel, and varied how much of each was used depending on such things as the running temperature, and load on the engine. The vehicle would have two fuel tanks, one gasoline and one Diesel. Theoretically that duel fuel engine delivers better MPG's and lower pollution.

I have read about that too. It's a compression-ignition engine that runs on a mix of gasoline and diesel. The diesel, with its higher cetane number, initiates combustion, while most of the power comes from gasoline. I think the ratio ranged from 10-50% diesel.

 

[KrisZ]

Originally Posted By: Tegger
If you're looking for some kind of savings by running urea, I suspect that any savings on fuel may be quickly eaten up -- or exceeded -- by the cost of the urea and its associated equipment. If urea were less costly, wouldn't the automakers be using it already?


Don't be too quick to assume that big corporations have it all figured out and that if they're not using something it means it is not effective. Quite contrary, most innovations come from small companies or even individuals. Please google Britten V1000 motorbike and see how one man stunned the whole motorcycle industry with his innovative and cutting age, for the time, technologies.

Also I don't think you understand my concept. I'm not looking to run urea injection as some sort of add on to existing emission system and engine fuel management. This would accomplish nothing.
What I'm proposing is building a system that would intentionally run lean, just like Honda Civic VX did and it achieved around 50mpgs combined! But those old Civics produced a lot of NOx, which was fine at the time, but it would not meet current emission standards.
My proposal would be to do the lean burn, but treat the exhaust gasses with urea to meet current NOx emission limits.

I would gladly pay for the urea fluid if it meant 40-50 mpg gas vehicle vs. a hybrid or diesel.

 

[Tegger]

Originally Posted By: KrisZ
most innovations come from small companies or even individuals.

Urea is not an "innovation" anymore, but is standard industry practice; all road trucks now use it.

Originally Posted By: KrisZ
I'm not looking to run urea injection as some sort of add on to existing emission system and engine fuel management.

Can urea control HC and CO? If not, then you would still need the existing systems, and urea would be an add-on.

Originally Posted By: KrisZ
What I'm proposing is building a system that would intentionally run lean, just like Honda Civic VX did and it achieved around 50mpgs combined! But those old Civics produced a lot of NOx,

The VX had an NOx adsorption cat in addition to the usual TWC; the VX put just about nothing out the tailpipe.

Originally Posted By: KrisZ
I would gladly pay for the urea fluid if it meant 40-50 mpg gas vehicle vs. a hybrid or diesel.

YOU would pay. I suspect that many other consumers would get quite annoyed about having yet another tank to fill up on a regular basis. And the Feds would surely enact a law like the one that now exists for trucks, where the engine is forced to stop running if the urea tank runs dry. No thanks.

 

[expat]

"
I would gladly pay for the urea fluid if it meant 40-50 mpg gas vehicle vs. a hybrid or diesel."


Why?

Personally I'd love to buy one of the TDI Diesels that are readily available in the 'Rest of the world'

Why would you want a Gasser?

 

[KrisZ]

Originally Posted By: expat
"
I would gladly pay for the urea fluid if it meant 40-50 mpg gas vehicle vs. a hybrid or diesel."


Why?

Personally I'd love to buy one of the TDI Diesels that are readily available in the 'Rest of the world'

Why would you want a Gasser?


Because, assuming that all the emission controls and exhaust are the same as in today's gas cars and the only modification is added urea injection and lean burn, you are not adding any complexity to the already existing and proven system and the added cost should be smaller than diesel or hybrid powertrains.
On top of that you don't have to deal with DPF's, glow plugs, cold start issues, long warm up times for short trips and higher diesel prices. Basically you would have all the benefits of a gasser with diesel like fuel economy.
I guess with a hybrid it would be a wash and would come down to price difference.
All of the above would be based on the assumption that the whole thing would turn out the way I described it. Of course I have no idea of the actual cost or fuel economy gains, if any, if such a system was ever implemented.

This thread is meant just to stirr up the discussion about something that, to me and so far Shannow, looks like it could actually work. We have some smart technical people here with various backgrounds that I thought we could have a nice discussion going, that's all.

 

[rslifkin]

Originally Posted By: KrisZ
cold start issues


Not an issue on the newer VW TDIs at least. If you leave the key on for a couple seconds to warm the glow plugs before cranking, my roommate's 2010 TDI lights off faster than the Jeep does at temps under 10* F.

 

[expat]

I have friends in Europe that have had TDI's (Ford, Peugeot, Citroen, Renault) for over 20 years, and have held-on to their cars in one case for over 12 years.
They do not see the problems you speak of. They start and drive just as they would a Gas car even in sub zero weather.

I asked one lady about waiting with the ignition on (pre heat) on cold days and got a blank stare!
I guess she just cranks and starts.

Sure in some regions Diesel can cost more (others it costs less) but remember Diesel does produce more BTUs (about 20%) than Gasoline.

What you suggest, and it is a valid area of discussion, to me, just seems add more complication to a Gas engine, that will then still require a revised emission control system, to accommodate a 'Lean Burn' in addition to the need to add Urea!
Something that seems to strike fear into many Americans ;-)

 

[JimPghPA]

After reading post here on BITOG about how VW has a useless warranty where the dealers blame everything on the customer abusing the vehicle and refuse to fix things under warranty, I consider VW to be on my list of cars I would never want, and that is a short list so far. Chrysler (totally ripped me off by having the rustproof bay inside of the dealership actually being a separate company that declares bankruptcy to avoid paying for vehicles rusting out) , Jaguar (because anyone who owns one has a never ending list of thing that require fixing, never ending because by the time they get every thing on the list fixed), there is a whole new list of thing that require attention, and now also VW because of their useless warranty.