EPA mulls over urea-injection rules

http://www.autoblog.com/2006/08/29/epa-mulls-over-urea-injection-rules/

http://www.autoweek.com/apps/pbcs.dll/article?AID=/20060829/FREE/60828027/1041/PROMOBLOG01

The EPA is considering rules that will require the vehicle to eventually stop running if drivers don't keep the tank filled.

Karl Simon, the EPA's assistant director for the office of transportation and air quality, said the agency is focusing on an early-warning system that notifies drivers when the urea tank is low.

The agency also is considering an inducement that forces drivers to refill the urea tank - for example, preventing the engine from starting if the tank is empty or automatically locking the fuel filler door until the urea supply is replenished.

The agency says automakers will have to make it easy for drivers and technicians to identify the urea tank and refill it.

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Let's see if we can be grown up with the urea jokes, OK, guys?

the solution of having the tank re-fill occur at the same time the oil change is due makes sense. However, I am NOT keen on the idea of permitting the dealership to be the only one that can perform this service.

SpinDaddy, you hit the nail right on the head! Not only are the EPA anti-diesel, but also blindly pro-hybrid. That's why the EPA's mileage rating for hybrids are waaaay off! We don't hear diesel drivers complaining that they can't attain the EPA's mileage ratings, like we do from so may hybrid drivers.

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You won't have to (in theory):

Simon says the EPA also is focusing on:

Ensuring the urea system is tamperproof and can't be disabled. Since urea is injected into the vehicle's exhaust system, the engine runs normally without it.

Assuring that the system works in cold weather. Urea freezes at about 11 degrees Fahrenheit.

Widespread availability of urea. It could be sold at auto parts stores, quick lube shops, dealership service departments and gas stations.

Assurance that the urea refill interval is at least as long as the manufacturer's oil change interval so both items can serviced at the same time by the dealership.

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I'm still having trouble seeing this as anything other than a stopgap solution while waiting for a much better technology. Honda claims to be able to meet emissions standards without any additive-based aftertreatment system, and the ideal system would be comparable to a catalytic converter in terms of longevity. Widespread availability of the additive is their best hope to make this viable, because otherwise people will gladly circumvent whatever "tamper-proofing" is put in place, just to get their car to run. (Plus a person with deep enough pockets and an immobilized car will easily get pissed to the point of legal action against the manufacturer.) Unless this really is the wave of the future, which I doubt, I can see these cars trading at a significant discount on the used market.

This may be the solution to the "stop at a gas station for a bathroom break only"... you could fill up both tanks!

istewart said:

I'm still having trouble seeing this as anything other than a stopgap solution while waiting for a much better technology. Honda claims to be able to meet emissions standards without any additive-based aftertreatment system, and the ideal system would be comparable to a catalytic converter in terms of longevity. <...>

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Not quite, the additive in the adsorber-based systems is raw fuel. Gotta get them electrons from somewhere. But it is likely that exhaust treatment will see a few iterations before settling down.

blacka5 said:

Not quite, the additive in the adsorber-based systems is raw fuel. Gotta get them electrons from somewhere. But it is likely that exhaust treatment will see a few iterations before settling down.

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Well, that's the one additive that the car needs to move, although if it causes a stark negative effect on mileage then it'd probably have even worse trouble with regards to marketing. The diesel Accord in the UK seems to be on par with the Jetta for fuel consumption, though, but I don't know if it's running their exhaust treatment system yet.

Somebody please explain to me, why should diesel cars be subject to a standard that no gasoline car has to meet? Why shouldn't gasoline powered vehicles have a no-start condition when there is a fault in their emissions system? Aren't gasser owners compelled to keep their cars in good tune to avoid pollution?

Bluetec not Carb Legal

Edmunds reports Mercedes Bluetec not able to pass emissions in California!

STUTTGART, Germany — The soon-to-be-launched and much-hyped Mercedes-Benz E320 Bluetec has reportedly failed to meet emissions criteria in the important states of California, Maine, Massachusetts, New York and Vermont.

Mercedes said its E320 CDI was "the cleanest diesel vehicle in the world," but apparently not clean enough for U.S. regulators.

Despite their popularity in Europe, diesels have never been commonplace in the United States and have a reputation as a technology for big rigs only. But there's a more ecological explanation for the lukewarm reception. Diesel is actually more harmful to the environment than gasoline because it generates more nitrogen oxides (NOx), gases that play a major role in the formation of acid rain and haze.

It is no wonder, then, that many U.S. states impose strict emissions levels for diesel-powered vehicles. European regulators in turn have begun to demand "NOx traps" for diesel vehicles.

Mercedes-Benz tried to tackle the problem by utilizing a catalytic device that converts NOx to nitrogen. Its Bluetec system, introduced in the Vision GL320 concept shown at the North American International Auto Show in January, injects an aqueous urea fluid called AdBlue into the exhaust system. AdBlue is intended to separate NOx into hydrogen and water.

Despite the setback in the United States, Mercedes has already been using Bluetec-equipped commercial vehicles for some time, and it plans to offer Bluetec-equipped cars in Europe by 2008.

What this means to you: Diesel is more frugal, but presents unique emissions problems for engineers. Sooner or later, it's got to work — Mercedes isn't the only one desperate to get modern diesels, so popular in Europe, into the U.S.

CA is trying to get the next generation of OBD to have a transmitter so when the check engine light comes on it notifiys the DMV and the owner will get a letter saying they have to have their car fixed. Next they will have it notifiy the police when I speed.

MrMopar said:

Aren't gasser owners compelled to keep their cars in good tune to avoid pollution?

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Yep, SMOG testing, works pretty well in California, don't pass the smog test = no registration = car gets impounded if you drive it. Least that's how it used to be there for a while.

EPA ready to set urea guidelines

For the first time, the EPA is ready to hand drivers the responsibility for making sure a vehicle's emissions system works properly.

http://www.autoweek.com/apps/pbcs.dll/article?AID=/20060829/FREE/60828027/1041/PROMOBLOG01

MrMopar said:

Somebody please explain to me, why should diesel cars be subject to a standard that no gasoline car has to meet? Why shouldn't gasoline powered vehicles have a no-start condition when there is a fault in their emissions system? Aren't gasser owners compelled to keep their cars in good tune to avoid pollution?

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The OBD-II system for gassers can adjust the engine emissions parameters to compensate for part failures.
Timing, fuel richness, injection, EGR cycle, etc.

But if the urea additive is depleted it would most likely affect the
system as a whole so greatly (for emissions) that the computer
wouldn't be able to compensate.

jackbombay said:

Yep, SMOG testing, works pretty well in California, don't pass the smog test = no registration = car gets impounded if you drive it. Least that's how it used to be there for a while.

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There's talk up here in WA State that the state will stop emission
testing in the next few years because the turnover lever has reached
a level of saturation of cleaner emission vehicles attributing to a
very small amount of failures being found.

MrMopar said:

Somebody please explain to me, why should diesel cars be subject to a standard that no gasoline car has to meet? Why shouldn't gasoline powered vehicles have a no-start condition when there is a fault in their emissions system? Aren't gasser owners compelled to keep their cars in good tune to avoid pollution?

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If it makes you feel any better the next generation of direct injection gassers will also have a NOx problem, at least when running in lean-burn cruise mode. They might not run quite as lean, in which the adsorber might be good enough, but then they'll take a hit in efficiency.

the current FSI engines powering VW and Audi has the lean burn mode
disabled thus sacrificing a fair bit of mpg's. the mechanics told me that
some of the intake plumbing (?) for the lean burn mode is also missing.

I looked up the definition of FSI a while back and found that FSI in europe
stands for something different than FSI in the US.

blacka5 said:

If it makes you feel any better the next generation of direct injection gassers will also have a NOx problem, at least when running in lean-burn cruise mode. They might not run quite as lean, in which the adsorber might be good enough, but then they'll take a hit in efficiency.

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cmc said:

the current FSI engines powering VW and Audi has the lean burn mode
disabled thus sacrificing a fair bit of mpg's.

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That's because the air-fuel ratio is far from stoichiometric, which means the exhaust is oxidizing and you don't have nearly enough partially burnt carbon to reduce the NOx. Sound familiar? To make it stoichiometric you have to throttle back the airflow, which drops efficiency.

Fix the diesel NOx issue and you've fixed lean-burn gasser NOx. Or do it the other way round if you like.

blacka5 said:

That's because the air-fuel ratio is far from stoichiometric, which means the exhaust is oxidizing and you don't have nearly enough partially burnt carbon to reduce the NOx. Sound familiar? To make it stoichiometric you have to throttle back the airflow, which drops efficiency.

Fix the diesel NOx issue and you've fixed lean-burn gasser NOx. Or do it the other way round if you like.

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Right observation but not sure the chemistry is correct... my understanding is that it is the excess heat that occurs in a lean burn situation that causes NOx formation. Is it really that the CH radicals are destroying NOx or that having an excess of unburned HC around is soaking up the O radicals floating about so they have a lower probability of completing their death dance with N2 and forming NOx.

Because I think the engine research shows that if you can reduce the temperature in the cumbustion chamber, even in a lean burn mode, that you will lower NOx. But I will defer to the TDIMeister and others on that one.

But on the UREA thing I'm all for preventing engine start, after adequete warning. I have long advocated turning of every non-safety item in the car to entice the driver to fill the urea tank. No Air, radio, auto anything, heated seats, etc... until you comply!

Just make the decision EPA and get it over with....

tdiesling said:

Edmunds reports Mercedes Bluetec not able to pass emissions in California!

STUTTGART, Germany — The soon-to-be-launched and much-hyped Mercedes-Benz E320 Bluetec has reportedly failed to meet emissions criteria in the important states of California, Maine, Massachusetts, New York and Vermont.

Mercedes said its E320 CDI was "the cleanest diesel vehicle in the world," but apparently not clean enough for U.S. regulators.

Despite their popularity in Europe, diesels have never been commonplace in the United States and have a reputation as a technology for big rigs only. But there's a more ecological explanation for the lukewarm reception. Diesel is actually more harmful to the environment than gasoline because it generates more nitrogen oxides (NOx), gases that play a major role in the formation of acid rain and haze.

It is no wonder, then, that many U.S. states impose strict emissions levels for diesel-powered vehicles. European regulators in turn have begun to demand "NOx traps" for diesel vehicles.

Mercedes-Benz tried to tackle the problem by utilizing a catalytic device that converts NOx to nitrogen. Its Bluetec system, introduced in the Vision GL320 concept shown at the North American International Auto Show in January, injects an aqueous urea fluid called AdBlue into the exhaust system. AdBlue is intended to separate NOx into hydrogen and water.

Despite the setback in the United States, Mercedes has already been using Bluetec-equipped commercial vehicles for some time, and it plans to offer Bluetec-equipped cars in Europe by 2008.

What this means to you: Diesel is more frugal, but presents unique emissions problems for engineers. Sooner or later, it's got to work — Mercedes isn't the only one desperate to get modern diesels, so popular in Europe, into the U.S.

Click to expand...

This is NOT the engine that TDIMeister posted about. The engine that failed was not using UREA injection.

testy_SOB said:

Right observation but not sure the chemistry is correct... my understanding is that it is the excess heat that occurs in a lean burn situation that causes NOx formation. Is it really that the CH radicals are destroying NOx or that having an excess of unburned HC around is soaking up the O radicals floating about so they have a lower probability of completing their death dance with N2 and forming NOx.

Click to expand...

You have to distinguish combustion chemistry from what happens in the cat. Gassers convert most of the fuel to CO2 and water, but leave significant quantities of partially burnt fuel (I'll call them VOC but actually also include very fine particles). Heating air produces NOx, and both the NOx and VOC are swept out of the piston. VOC + NOx = ozone as soon as they hit sunlight, so you want to convert both the VOC and NOx to photochemically unreactive species, namely CO2 and N2. To get from VOC to CO2 you need to oxidize the carbon; to get from NOx to N2 you need to reduce the N. Well isn't that convenient -- we can use the VOC to reduce the NOx and the NOx to oxidize the VOC. That's what the cat does.

Diesel uses less fuel (carbon) than gassers, burns it more efficiently, and runs a much higher air fuel ratio. So there is less carbon to begin with, less of which is reduced, and you've got a ton of oxygen in the exhaust stream (for gassers that oxygen is largely locked up in CO2 and H2O) This is a strongly oxidizing environment, so you just don't have enough reductant to convert the NOx to N2 (but getting the VOC to CO2 is easy). The approaches used so far are 1) add a reduced species, urea seems to be the additive of choice or 2) adsorb the NOx on something which you periodically hit with raw fuel (reduced C) which reduces the N and drives it off as N2 while converting the raw fuel to CO2 + H2O.

GDI in cruise mode runs air-fuel ratios similar to diesel, so the exhaust stream has too much O2 and not enough VOC for a standard gasser cat.

Because I think the engine research shows that if you can reduce the temperature in the cumbustion chamber, even in a lean burn mode, that you will lower NOx. But I will defer to the TDIMeister and others on that one.

Click to expand...

You do have some control on NOx at the combustion level by reducing the combustion temperature, but as long as you have combustion in a 78% N2/21% O2 air charge, you'll get NOx, hence the use of exhaust treatment.

blacka5 - are you familiar with "adiabatic flame temperature"? I'm not an engineer, but it's my understanding that flame temperature peaks at stoichiometric and decreases (linearly?) as you get leaner (or for that matter, richer) air/fuel ratios.

If this is correct, wouldn't in-cylinder NOx formation be HIGHER in stoichiometric ICEs (i.e., gasoline engines) than lean burn ICEs (i.e., diesel engines and GDI gas engines)?

I've read references that state that engine-out NOx from diesel engines is significantly lower (by a factor of four or five, IIRC), while other references state that engine-out NOx is higher from diesel engines. I'd think that engine-out NOx would be higher from gas engines than diesel engines based on the adiabatic flame temperature concept (assuming it's applicable to ICEs). Any insight on which is correct?

There are two things happening at the same time. If all else were equal, which it never is, adiabatic flame temperature is highest at stoichiometric air/fuel ratio. But, stoichiometric air/fuel causes most of the oxygen to get locked up in CO2 and H2O rather than allowing it to react with N2. As you go rich of stoichiometric, NOx drops both because O2 gets used up but also as flame temperature drops. As you go lean of stoichiometric, NOx goes up at first - although the flame temp is dropping, the amount of available O2 is increasing. As you go way leaner than that, NOx starts dropping because the effect of lowering the temperature is stronger than the effect of increasing the O2. Then the engine misfires.

Why does a lean-running gasoline engine have a high exhaust temperature? because although the PEAK temperature in the cylinder might be lower, a lean mixture burns SLOWER, extending combustion later into the power stroke, so that combustion shows up as heat rather than power. That's why a super-lean-tuned engine doesn't necessarily get fantastic mileage; you need special fast-burn combustion chambers and really good ignition to make this work.

Complicating this, diesel combustion is not uniform, it occurs on a droplet scale. Even if the average flame temperature is low, the combustion and the NOx formation are happening where the fuel-rich droplet is diffusing into the fuel-lean surroundings. Hence the R&D into HCCI (Homogeneous Charge Compression Ignition) ...

The engine-out emissions depend on so many factors that I don't think it's possible to make a general statement about engine-out NOx being higher or lower with gas or diesel.

For current VW TDI, the tailpipe NOx is the engine-out NOx because the catalyst doesn't do anything about it. It's controlled by EGR, injection timing, combustion chamber design, intake charge cooling. It's quite likely that a normal gasoline engine would have higher engine-out NOx because they rely on the catalyst. But, some engines use EGR and some don't. Some deliberately run rich and have air-injection to get it stoichiometric at the catalyst, others run stoichiometric without air-injection. They may operate differently under various load conditions. Compression ratio and combustion chamber design have an effect, too. Too many variables.

Brian - thanks for the explanation.

understandable that edmunds got confused because i think mercedes was
somewhat sneaky about what their NOx control strategy was for the US
market.. so they chose to use their marketing term rather than giving
technical specifics. i'm guessing that when EPA won't OK urea injection
they did a last minute switch to adsorbers while keeping the marketing name.

adblue has always been synonymous with urea injection until very recently.

what was fascinating about the whole mercedes affair is the fact that they
launched the marketing full force before actually getting properly
certified!

testy_SOB said:

This is NOT the engine that TDIMeister posted about. The engine that failed was not using UREA injection.

Click to expand...

wxman said:

blacka5 - are you familiar with "adiabatic flame temperature"? I'm not an engineer, but it's my understanding that flame temperature peaks at stoichiometric and decreases (linearly?) as you get leaner (or for that matter, richer) air/fuel ratios.

If this is correct, wouldn't in-cylinder NOx formation be HIGHER in stoichiometric ICEs (i.e., gasoline engines) than lean burn ICEs (i.e., diesel engines and GDI gas engines)?

I've read references that state that engine-out NOx from diesel engines is significantly lower (by a factor of four or five, IIRC), while other references state that engine-out NOx is higher from diesel engines. I'd think that engine-out NOx would be higher from gas engines than diesel engines based on the adiabatic flame temperature concept (assuming it's applicable to ICEs). Any insight on which is correct?

Click to expand...

I'm not an engine guy -- I know what an adiabatic flame temperature is, but not how close ICEs get or under what load conditions or what typical duty cycles are -- GoFaster's explanation will be better than mine. I'd only add that neither charge nor temperature distribution will be homogeneous. About the only thing that will will be the N2/O2(/Ar/etc) distribution in the airflow. So even if you get an optimal burn in an optimal charge (which will likely be stratified anyway these days) you won't get an optimal (homogeneous) temperature field for both combustion efficiency and NOx production. You will also get a thermal gradient across the fuel droplet, far more so with diesel because of its low burn rate, hence the recent drive to smaller and smaller droplets from higher and higher pressure injectors (I think conventional wisdom has it that gasoline is fully vaporized, but I'm not certain about that, given the partitioning of gasser PM into the UF and nanoparticle fractions. But perhaps all gasser PM is secondary). Maybe HCCI will help, OTOH they've been working that for a while.

blacka5 said:

You have to distinguish combustion chemistry from what happens in the cat. Gassers convert most of the fuel to CO2 and water, but leave significant quantities of partially burnt fuel (I'll call them VOC but actually also include very fine particles). Heating air produces NOx, and both the NOx and VOC are swept out of the piston. VOC + NOx = ozone as soon as they hit sunlight, so you want to convert both the VOC and NOx to photochemically unreactive species, namely CO2 and N2. To get from VOC to CO2 you need to oxidize the carbon; to get from NOx to N2 you need to reduce the N. Well isn't that convenient -- we can use the VOC to reduce the NOx and the NOx to oxidize the VOC. That's what the cat does.

Diesel uses less fuel (carbon) than gassers, burns it more efficiently, and runs a much higher air fuel ratio. So there is less carbon to begin with, less of which is reduced, and you've got a ton of oxygen in the exhaust stream (for gassers that oxygen is largely locked up in CO2 and H2O) This is a strongly oxidizing environment, so you just don't have enough reductant to convert the NOx to N2 (but getting the VOC to CO2 is easy). The approaches used so far are 1) add a reduced species, urea seems to be the additive of choice or 2) adsorb the NOx on something which you periodically hit with raw fuel (reduced C) which reduces the N and drives it off as N2 while converting the raw fuel to CO2 + H2O.

GDI in cruise mode runs air-fuel ratios similar to diesel, so the exhaust stream has too much O2 and not enough VOC for a standard gasser cat.



You do have some control on NOx at the combustion level by reducing the combustion temperature, but as long as you have combustion in a 78% N2/21% O2 air charge, you'll get NOx, hence the use of exhaust treatment.

Click to expand...

OK... let me get this straight ... (normally I'd spend more time getting references and check my own assumptions and such) you are saying that in order to convert NOx to N2, you have to depnd on what is essentially a 3rd order rxn? Isn't that about as controllable as a flock of seagulls? I thought that 3 way catalysts were so named becuse they had a mix of catalysts, one for each of the main pollutants.

Point me at a reference... When my 80 hour weeks end I'll look it up...

testy_SOB said:

OK... let me get this straight ... (normally I'd spend more time getting references and check my own assumptions and such) you are saying that in order to convert NOx to N2, you have to depnd on what is essentially a 3rd order rxn? Isn't that about as controllable as a flock of seagulls? I thought that 3 way catalysts were so named becuse they had a mix of catalysts, one for each of the main pollutants.

Point me at a reference... When my 80 hour weeks end I'll look it up...

Click to expand...

Sorry... just saw Brians reply and that is cocnsistant with my fading recollections....

Need SLeeeppppppppp