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E320 BLUETEC Arriving as a 45-State Vehicle; Urea SCR Required for 50-State Rating

28 August 2006

E320_bluetec
The E320 BLUETEC. Click to enlarge.

When the Mercedes E320 BLUETEC hits salesrooms shortly, it will be as a 45-state compliant vehicle, not a 50-state vehicle. (Earlier post.)

BLUETEC is DaimlerChrysler’s modular emissions aftertreatment architecture that provides the potential for 50-state compliance—i.e, meeting EPA Tier 2 Bin 5 emissions levels, which map to California LEV II levels.

To tackle the difficult NOx target, DaimlerChrysler has currently defined two technology approaches.

The E320 BLUETEC, first of the family to arrive in the US, uses a newly developed NOx adsorber, a catalytic device that converts NOx to nitrogen. Subsequent family members are slated to use urea-based injection system for NOx reduction (using an aqueous urea solution called AdBlue, the genesis of the BLUETEC name).

Both are combined with Selective Catalytic Reduction systems, which, while in principle are the same, differ in application design based on vehicle parameters and emissions targets. (Earlier post.)

E320
Emission Bins and the results of 2004 testing of an E320 prototype. Close, but no Bin 5. Click to enlarge.

Although the E320 BLUETEC comes “quite close” to Tier 2 Bin 5 NOx levels, according to a DaimlerChrysler spokesperson, “the urea SCR system will be necessary” for full 50-state compliance.

Tests by the EPA in 2004 of a E320 prototype indicated that the aftertreatment system came in at just beneath 0.06 g/mi of NOx; the Tier 2 Bin 5 target is 0.05 NOx g/mi. (See graph at right.)

The EPA has yet to sign off on urea-SCR systems for light-duty vehicles, partly due to concerns on enforcement. It is clear, however, that urea-SCR is going to be necessary to support a full 50-state rollout of most clean diesel vehicles. The EPA said at the recent DEER 2006 conference that it would soon provide guidance to manufacturers on urea-SCR systems for light-duty vehicles.

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August 28, 2006 in Diesel, Emissions | Permalink | Comments (26) | TrackBack (1)

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Will the OBD system for diesels prevent people from operating without Urea for the 50-state compliant models?

You can sell a car with extra requirements but there are no guarantees people will follow those requriements. Example: I know of people who put 87 octane in cars designed for 91 octane...lucky for them modern vehicles of this nature usually have knock sensors to pull the ignition timing and move to less aggressive fuel maps.

And importantly, how easy will it be to get AdBlue when you run out? And how long will it last? I'd hate to run out of the stuff in the middle of the desert, or a snowstorm.

The whole OBD question is still being worked out in terms of scope, phase-in, etc. From what the automakers were saying at DEER, they're going to make refilling as easy as possible. They're talking about a number of different approaches, from having the replenishment of the urea timed to service intervals, to having quick fill-and-go supplements you could buy at filling stations, to stocking AdBlue in auto parts stores, etc.

Cervus,
Or how about running out of AdBlue in crawling urban/suburban traffic during hot summer months.
_One possibility would be for them to have a large enough tank of this AdBlue. Every 10,000 miles, you go in for a tuneup anyway. A container with enough to 11,000 or 12,000 would be enough. That way, with your tuneup, you will get a refill of AdBlue, and maybe an oil/filter or tranny fluid change too.
_
___As engines themselves become cleaner and more efficient, the amount of AdBlue needed will likely decrease. There might be a point that Adlue will not be needed for NOX.

There might be a point that AdBlue will not be needed for NOX reduction.
_
___There is another possibility, in which the AdBlue is kept, but to meet ever more stringent emission levels.
_
___Here is a resource on EPA Tier2 standards, as well as LEV2 requirements:
http://www.dieselnet.com/standards/us/light.html
_
___As you can see, Tier 2 Bin 5 is just the beginning. Tier2 Bin2 and LEV2 SULEV will be no joke.

Not that a Mercedes owner is likely to hit up the local quick change oil station for their tune up needs but I could see this being a problem for any "average" vehicle equipped with such a solution.

Is everyone forgetting that the car drives fine without AdBlue, only with emissions slightly above the newest most stringent requirements? I'm sure you can drive home in the blizzard and fill up next time you buy fuel.

I wonder if AdBlue smells like piss? Because that's what it really is, right?

While an AdBlue tank large enough to cope between scheduled services is most convenient, I doubt that would be feasible. That must be an awfully large tank..? I think I would prefer a solution where a light switches on on the dashboard when it is time to replenish at the next gas station.

.......That must be an awfully large tank.?.....

Thomas, have you read somewhere how much of this urea is used, say in a mile, or as a percentage of diesel use? I have not read anywhere how much of this stuff is used. Could be a quart every mile, or possibly as little as a tablespoon every thousand miles. I just dont know. But I have to give the Mercedes engineers the benefit of the doubt that they have designed its storage, and use, to be somewhat bearable, if not just a slight nuicance. My thought is that it could be something like every 8-10k miles. That gives them the right to determine service intervals to replenish this stuff, while also maintaining other aspects of the cars maintenance. Maybe some sort of "red carpet" maintenance offering disguised to allow them to check this urea system out. My thoughts are that this will be taken out of the shade tree mechanics hands and be only offered as a dealer service. May not be an entirely bad thing. Lets see how this develops.

As a followup, I am sure the other automakers are curious how Mercedes will pull this off. Then, I am sure, when other automakers devise their systems they will offer better deals, and easier systems, and then the Mercedes will counter respond.

Does anyone know the source of this Adblue urea, and its supply versus demand?

Note that the 6cylinder CDI missed Nox by .01, 4 & 5 cyls should be there.

If a four or five cylinder could make the NOx standard then we'll probably be seeing a diesel Wrangler, PT Cruiser, and Caliber/Compass/Patriot in the near future.

"If a four or five cylinder could make the NOx standard then we'll probably be seeing a diesel Wrangler, PT Cruiser, and Caliber/Compass/Patriot in the near future."

I thought the whole point of pushing clean diesel is to have a new "premium" (and hopefully profittable) product for the market.

If automakers really believe that adding diesel to every line of cars will generate enough sales to boost the bottomline, I'm sure it would have been done so much sooner. Jeep Liberty CRD only sold about 10,000(?) units or so, over who knows how many years. To me, that means adding "diesel" to model "X" doesn't mean it will always sell.

I know emissions is always used as the main reason why there isn't more diesels being sold, but in the end, the sad truth is that fuel economy and emissions are not really the top reasons why people buy cars.

If Customer X happened to want a BMW 5-series, he/she would not care if Toyota/Lexus Hybrid, Passat TDI, or E320 BlueTec get better mileage. Tourag is probably a very capable SUV, but even offering a diesel version really didn't help when the market is pack full of so many competative choices.

What DC is doing here is really just spicing up the image of clean diesel marketing it only in the premium market. If it really does take off, we would more likely see a Chrysler 300 with BlueTEC, rather a low-margain vehicle like the PT Cruiser, or Calibre.

Ironically, development of NOx absorbers by diesel engine manufacturers drives final nail in the coffin of diesels for cars (heavy duty vehicles totally different matter). Currently direct injection gasoline engines have to maintain overall stoichiometric mixture (rich near spark plug, lean elsewhere) to keep their catalytic converters operational. Therefore their efficiency is only about 10% better then regular engines. With NOx absorber overall mixture could be lean 99% of the time – except for a moment of absorber’s regeneration, and efficiency gain is much higher – reportedly up to 30%. It approaches the efficiency of diesel engine, but without drawbacks of diesel. Add hybrid drivetrain, and we have a winner; plug in capability will follow.

Except that diesel engines can run off SVO or biodiesel, which is hugely more economically / agriculturally / CO2 balance viable than gasoline or ethanol.

That's by far the biggest advantage of the diesel engine.

Andrey, you forget one important component: Sulfur levels in gasoline. 15ppm or less is required to keep those special NOx catalysts alive and while diesel is mandated to be there gasoline is not. If gasoline were brought down to 15ppm or less throughout the US it would allow everybody with direct injection (mazda, vw/audi, mitsubishi, toyota) to instantly get a good 10-20% improvement in fuel economy and with current gas prices you know they would do it immediately. Mitsubishi's GDI engines in Japan run a 40:1 a/f ratio (typical is 14.7:1) for part load cruise and use NOx absorber catalysts.

AdBlue is a 35% aequeous solution of high purity synthetic urea (aka not urine). A precursor step in the catalytic chain converts the harmless urea into the active component, ammonia.

The additive consumption rate is approx. 3-4% of the fuel flow. Here in Europe, where SCR has already been adopted widely by HDV manufacturers and a distribution infrastructure now exists, the additive cost per US gallon (~$2.50) is about half that of diesel fuel (~$5).

---

EPA has expressed several reservations regarding the introduction of SCR in the US:

- nationwide availability of AdBlue additive. One idea is to store the urea in powder form and refill only the distilled water. The correct concentration would have to be maintained by a tamper-proof automated system. MB claims the SCR system for its passenger cars would be frugal enough to permit the distribution of (presumably imorted) AdBlue via its US dealerships only. Note that there are currently no plans to introduce the SCR variant in the EU, as emissions regs here can still be met with less expensive equipment.

- tamper-proof detection of low and empty AdBlue and volume by the OBD and, associated emergency operations mode. Burnt decades ago by unscrupulous US carmakers, EPA continues to assume the entire industry is full of crooks looking to undermine its clean air regulations. CARB is even more paranoid. By contrast, European regulators have accepted available sensor technology for measuring fluid level and urea concentration as adequate.

- anti-freeze protection for the AdBlue tank (the noral solution ices up at -11 deg C, i.e. 12 deg F).

- the reliable light-off temperature of the SCR catalyst package is around 250 deg C, i.e. 480 deg F. HDV engines are operated at high load most of the time, but even so, the NEDC used in vehicle certification permits higher exhaust temperatures than the equivalent US test procedures.

- even if the required gas temperature can be reliably sustained, the NOx conversion rate is currently limited to around 85% because of the open control loop and the need to avoid excess ammonia from entering the atmosphere. Once sufficiently fast and reliable NOx sensors become available, the conversion rate can be increased to 90-95% using closed loop control logic.

---

There are several alternatives to SCR technology, but they do present serious challenges of their own:

- NOx adsorbers do not require any additive and can operate using lower exhaust temperatures. However, the application effort requried for transparently alternating between the lean and slightly rich fuel mixtures required for adsorber technology is very high. Worse, the catalyst material is highly susceptible to sulphur poisoning. Even with ULSD (15ppm) and 10ppm diesel becoming available in the US and EU, respectively, between now and 2010, NOx adsorbers still require periodic sulphur purging. This requires exhaust temperatures of 650 deg C (1200 deg F) to be maintained for extended periods of time in a component located relatively far from the engine due to its bulk. Catalyst performance is permanently reduced to some extent after each sulphur purge cycle.

- HCCI largely avoids NOx production by eliminating combustion flames. Instead, the pre-mixed fuel ignites simultaneously throughout the chamber at the same time in a near-isochoric flash. Controlling this reliably, especially during load transients, is hard. When using diesel fuel (gasoil or similar), high charge motion, high-pressure fuel injection, high levels of cooled EGR, in-cylinder pressure sensors and powerful engine control logic are all required in addition to a variable gemoetry turbocharger. However, given the already advanced state of modern turbodiesel technology, the incremental cost would still be far lower than that for the lean-burn NOx exhaust gas aftertreatments described above.

Unfortunately, diesel HCCI only works when the engine is sufficiently hot and operating in part load (6-8 bar BMEP and <~15kW/liter of four-stroke displacement, <~3500 RPM). Above a certain load level, combustion noise becomes unacceptable. Besides, EGR levels cannot be as high at elevated loads, leading to NOx levels comparable to those produced in conventional combustion. The state of the art dictates that any HCCI-capable engine must operate using conventional combustion during warm-up, extended idling and at high load - and switch between combustion modes transparently wrt torque, emissions and noise levels.

---

Does all this mean that diesel engines are doomed to go extinct? No, but it is likely that the ever-more stringent emissions regulations will raise the economic threshold for diesel engines to MDVs, or at least large LDVs like full-size SUVs and pick-up trucks. This applies especially in the US, where diesel LDVs are exotic vehicles and gasoline electric hybrids are the fastest-growing market segmen.

By contrast, HDVs will continue to operate on diesel - many observers believe EPA will have little choice but to permit SCR systems for this vehicle class in the next few years. This would trigger the establishment of a distribution infrastructure for AdBlue at truck stops in the US.

I thought adblue was the latest gatorade flavor.

We're neurotic about particulates and NOx when CO2 is arguably the biggest problem. Diesels trump spark ignition engines in this regards. Why don't our myopic fed/state agencies get this?

-mt

Particulates kill you today. CO2 you have a much longer timetable to address the situation.

The problem is – particles have an atmospheric lifetime of hours to days (depending on size). CO2 has an atmospheric lifetime of decades. We need to start addressing CO2 emissions sooner rather than later.

It amazes me how all the marketing BS of Bluetec try to pass EPA reservations. There are true alternatives to Bluetec, including Toyota's DPNR. Do you know that in Europe first Euro4 diesels were HDI+FAP from PSA and D4D (without FAP) from Toyota? At least half year later other manufacturers came with their own version.
But in my country (Romania) Avensis D-CAT doesn't sell because poor quality of fuel (we have many 10ppm stations but quality of tanks is on low par). And I see many new Mercedes CDI with big smoke on tail-pipe. And I know many stories about clogged injectors, almost none on gasoline...
About polution: try to live in a city with most of car diesels, some of them with OBD sensor deactivated in service (for a small fee some services can deactivate any sensor).

Rafael:
Good to hear from you again.
Some additional comments. Due to unbelievable ignorance of US driving public, EPA and CARB are rightfully concerned about proper operation of SCR equipment in private LDV. Even for highly controlled HDV, there are some concerns. Couple of years ago HDV diesel engine manufacturers settled EPA suit (for record in EPA history multi billion dollar penalty) for programming on-board computers to move gradually to higher power/lower fuel consumption mode with elevated emissions as a consequence.

I do believe that SCR will be widely used in US on HDV as robust and proven technology, unlike NOx absorbers. BTW, there is one interesting twist. Synthetic urea is very energy demanding chemical, and according to calculations from the point of view of energy/cost it is more advantageous to use NOx absorber and waste some diesel fuel in afterburner to eliminate O2 presence in exhaust during periods of absorber’s regeneration, then use urea all the time. This equation is tipped to urea advantage in EU due to overpricing of diesel fuel.

As I mentioned before, NOx absorber is emerging technology, and hopefully will be developed to tolerate current sulfur levels in gasoline. Otherwise it will be another 10B$ to upgrade refineries to ultralow-sulfur gasoline…

In GDI engine with CVT (like in Prius), regeneration of NOx absorber could be easily and cheaply accomplished, unlike in diesel engine.

Slipping of urea with consequent unpleasant smell is emerging problem. This summer I have pleasure to spend one week in Vienna, and then in New-York. Air in NY is clean, which I can’t say about Vienna. Quite noticeably diesel cars to blame. I could only imagine some of them will smell pee in addition…

Andrey -

there are no diesel LDVs with SCR systems on the European market at all. The only operational vehicles with such systems are very new Euro-4 compliant HDVs, few of which can be found in city centers. All SCR systems feature a second oxydation catalyst downstream of the main unit, precisely to prevent the inadvertent release of excess ammonia into the atmosphere (as indicated above, open-loop control is used at present). If you can smell any ammonia, the concentration is already dangerously high. Functioning SCR systems do NOT emit urea in detectable quantities.

If you caught a whiff urine in either city, it wasn't because of vehicle exhausts. More likely, the source was domestic pets and/or vagrants.

As for general air quality, it is possible that you noticed a higher level of NOx-related smog (we had a heat wave all through July) and particulate matter contamination in Vienna than in NY. This is because the active vehicle fleet is heavily skewed towards diesel vehicles, many of which are older and were certified to Euro-1, -2 or -3 standards. It simply takes a number of years for the fleet to churn. Consumers do care about air quality, and many new Euro-4 compliant diesel cars are already sold with (typically optional) particulate filters.

Note that Vienna's city buses have run on LPG rather than diesel for many years.

I live in Portugal where diesel cars are everywhere.
Believe it or not, the pratical result of using that type of engine is low quality of life and air.
The air smells awfull, it burns your eyes and throat,(you can't ride a bike near a diesel car) there are walls completly black because of soot, but the most noticed problem is the way people are using them. People using gasoline cars usually get very good mileage because gasoline is expensive so they drive more carefully with better planing. Those driving gasoil cars, generally use it in a very diferent way (gasoil is much cheaper than gasoline)so they don't care if they polute or are not driving eficiently.
Gasoline engines are not so eficient but there´s no reason for it. They can run on hydrogen,ethanol, natural gas and could be as eficient (but they have to use very high octane rating fuel to avoid knocking)so the best way to use gasoline is HCCI combustion.
Low octane gasoline (wich is cheap and can be obtained from biomass) is the best fuel for full and partial load operations in real HCCI engine(HCCI diesel engine is not a real HCCI engine because it has a stratified and heterogeneous charge and is very expensive).
So i think diesel cars should disapear and be replaced by fuel eficient and clean real HCCI engines fueled by low cetane and low octane fuels (fischer-Tropsch gasoline for example).
Why should we have to buy particulate filters,nox depurators and very expensive engines when HCCI is clean, eficient and cheap.

To clear up some things:

Bluetec diesels offer better fuel-efficiency (6%), Adblue consumption will be around 3-4% of fuel consumption. AdBlue does not smell like urea. It smells synthetic. Petrol is not that fragrant as well...


At the guy above me:
Todays diesels does not smell anymore. if you have ever driven a modern diesel by Citroen or BMW you would know that.

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