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Mercedes-Benz Introduces the E320 BLUETEC Diesel in California

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E320 BLUETEC.

Mercedes-Benz USA (MBUSA) is introducing a limited number of its E320 BLUETEC diesel sedans in California. The sedan is now available through a special two-year/24,000-mile lease, and is lease-priced on a par with its gasoline sibling, the E350.

At its initial US introduction, the E320 BLUETEC slightly exceeded the CA LEV II, EPA Tier 2 Bin 5 emissions threshold, and so was not put on sale nationwide. (Earlier post.) To meet the stricter standards of California and the other LEV II states, Mercedes-Benz made some modifications to the aftertreatment system, including changes in the control software. Although the catalyst material used in the NOx catalyst is the same, the unit is slightly different, according to Professor Dr. Herbert Kohler, Vice President, Group Research & Advanced Engineering Vehicle and Powertrain, Mercedes-Benz Cars and Chief Environmental Officer for Daimler AG.

Illustration_ofimg_4042
Aftertreatment system for the E320 BLUETEC. Click to enlarge.

The E320 BLUETEC features a new-generation 3.0-liter V6 diesel engine. The new 72-degree V6 diesel features four valves per cylinder, dual overhead camshafts and centrally located piezo-electric fuel injectors. Designed to spray diesel fuel directly into the center of the combustion chamber, each injector is positioned in the aluminum cylinder head about where a spark plug might be found on a four-valve gasoline engine. This layout ensures even dispersion of fuel as its flame front spreads concentrically across the combustion chamber.

Although many non-turbo diesel engines have compression ratios higher than 20:1, Mercedes engineers found that, in conjunction with the BLUETEC engine's exhaust-driven turbocharger, the engine is most efficient with a compression ratio of 16.5:1. The turbocharger features Variable Nozzle Turbine (VNT) technology which is integrated with the electronic engine management system. To vary the combustion air volume quickly, VNT adjusts the guide vanes electrically as load and engine speed conditions change.

Diesel engines usually operate without any throttle in the intake system, so that fuel delivery alone controls engine load and speed. However, Mercedes engineers found that, at light load, throttling one of the two diesel intake ports on each cylinder creates air turbulence that helps optimize the combustion process and further reduce fuel consumption and exhaust emissions. The BLUETEC engine makes use of electronic intake port deactivation that’s automatically managed by the electronic control unit.

The quick piezo-electric injection system enables the application of a few pilot injections in rapid succession just milliseconds before the main injection to pre-heat the combustion chamber, thereby making pressure and temperature increases more gradual. Smoothing out combustion pressure and temperature spikes softens the usual diesel noise and reduces oxides of nitrogen formation as well.

In addition to using pilot injection and exhaust gas recirculation to minimize oxides of nitrogen, the E320 BLUETEC engine features an advanced-technology NOxstorage catalyst that temporarily stores oxides of nitrogen. Regeneration pulses release a form of nitrogen oxide that reacts with exhaust gas to become nitrogen. Control of these regeneration events was one of the modifications made to bring the E320 into compliance with LEV II.

The 208 hp, 400 lb-ft E320 BLUETEC carries a fuel economy rating of 35 mpg.

The California lease program will function as a bridge as MBUSA prepares to begin phasing in 50-state BLUETEC vehicles nationwide starting in 2008. The first step will be the extension in January 2008 of the special lease program to other states which have adopted the California emissions standards and so which do not currently allow sales of new diesel automobiles.

Later in 2008, Mercedes will introduce another BLUETEC system on its M-, R- and GL-Class vehicles. This system utilizes AdBlue injection, a process that adds precisely measured quantities of a urea-based solution into the exhaust stream which enhances long-term emissions performance sufficient to meet the Tier 2 Bin 5 standards.

MBUSA will offer 50-state diesels across its SUV model lines (M, GL and R-Class) late next year and will continue to add to its alternative powertrain offerings, with BLUETEC mild hybrids, two-mode gasoline hybrids, and more BLUETEC models announced to be delivered over the next few years. (Earlier post.)

Comments

Elliot

I don't know about the aftertreatment idea, but this seems like a good program. Hope it works out and they eventually make bluetec standard. I'm really looking forward to their hybrids, and if Mercedes has actually improved reliability since their split with Chrysler, then I'm considering one. If it's sporty at least, and if I can afford it, which is more my problem than theirs.

Nick

Cool. I want a scaled-down (4-cyl), micro-hybrid version of this powertrain in something like a Toyota Rav4 or Subaru Forester. 45mpg, practical packaging and all-wheel drive for the snow would be my dream ride.

BTW, why a 72-deg V6? I though 60-degrees made sense if you have three crankshaft throws?

Jorge

Nick,
60 degrees V-6 is for six crankshaft throws. The fire intervals are all 120°.
90 degrees V-6 is for three crankshaft throws and the fire intervals are 150°-90°-150°-90°....

Regarding the 72° V-6, I do not know how many throws the crankshaft has and don't know the fire intervals.

Rafael Seidl

Note that this E320 features a lean NOx trap rather than a urea injection system. Apparetently, with some modifications they were able to get it to meet T2B5 = LEV II.

Setting the lease price on par with the gasoline variant is a market introduction gimmick, since the diesel engine + DPF + LNT are more expensive to produce than a gasoline engine + 3-way converter.

@ Jorge -

you can adjust for a bank angle other than 60 degrees by splitting each crank into two portions with a compensation offset to achieve the desired firing interval of 120 degrees crankshaft. The compensation offset for a bank angle of 72 degrees is 72-60 = 12 degrees, so the two portions have a lot of overlap, which is good for mechanical strength and stiffness of the crank.

Nobody mass produces a V-engine with fully separate cranks for each piston these dayas - there is simply no need.

Nick

Rafael--

"you can adjust for a bank angle other than 60 degrees by splitting each crank into two portions with a compensation offset to achieve the desired firing interval of 120 degrees crankshaft. The compensation offset for a bank angle of 72 degrees is 72-60 = 12 degrees, so the two portions have a lot of overlap, which is good for mechanical strength and stiffness of the crank."

I was wondering if it was something like that. I was sure they would design for evenly distributed firing one way or another.

DieselHybrid

My only question is- why the trend in decreasing diesel compression ratios (CR)? My father's '81 VW Dasher Diesel had a 22:1 CR. Now MBUSA latest offering has a measly 16.5:1 CR?

Correct me if I'm wrong, but it would seem to me that the higher the CR the higher the thermodynamic efficiency. I need to review my thermo books, but the higher CR approaches the ideal Carnot cycle- right?

I can only think the lower CR helps achieve lower levels of NOx emmissions. Anyone?

Rafael Seidl

@ DieselHybrid -

ever-stricter NOx emissions regs are indeed the main reason for the falling geometric compression ratios.

There are other reasons as well, though. First, modern variable geometry turbine or sequential turbo concepts can deliver more boost, especially if the intercooler is very effective. Therefore, while the theoretical thermodynamic efficiency suffers when the compression ratio is reduced, the actual SFC improves because larger turbos are more efficient and smaller engines (e.g. with fewer cylinders) don't lose as much power to internal friction.

Second, you have to weight the additional thermodynamic efficiency of a higher compression ratio against the additional mechanical strength required to contain it. Additional engine mass implies beefier mounts and chassis structures. Engine fuel efficiency is not quite the same thing as vehicle fuel economy, which is what really matters. One of my professors claimed that the ideal compromise for a vehicle would be an engine with a compression ratio in the 14-15 range.

Gasoline engines cannot go that high because of the low octane rating of the fuel - modern naturally aspirated designs max out at ~11.5 (~10 for a boosted concept). Only if you switch to a high-octane fuel like neat ethanol, methanol or natural gas can you go higher.

Diesels cannot yet go that low because the engine must reliably start even in extremely cold weather. Modern high-power glow plugs are easing this constraint, such that ratios of 15.5-16.5 are now possible though not yet common.

Third, there is NVH, which gets worse with increasing compression ratios. In Europe, vehicle noise emissions are restricted.

Aussie

Who checks when the NOx catalyst (either type) runs out? I'm thinking state authorities might pull over these cars and take tailpipe samples. If they don't there's no real point to the regulations.

Joseph


MB said they would be checking the system at every service interval. If a person avoided the dealership the yearly emissions inspection would catch it.

Rafael Seidl

@ Aussie -

(a) a lean NOx trap (LNT) uses a special washcoat for a regular ceramic monolith. The composition is that of a standard three-way catalyst (i.e. some combination of Rhodium, Palladium and Platinum) plus an adsorption material, e.g. barium oxide. At low exhaust gas temperatures, NOx binds to these receptor sites. After a short while, the catalyst is saturated andmust be purged. The engine controller transparently switches from lean to slightly rich mixture operation, which means the exhaust gas is hotter and no longer contains any free oxygen. During these brief purge phases, the NOx desorbs and the device works as a standard three-way catalyst does. The slightly rich mixture ensures that there is enough CO and HC to reduce not just the NOx that is still being produced but also the desorbed fraction.

Pros: no catalyst is consumed, therefore no user action required to maintain functionality. Very effective even at generally low exhaust temperatures, i.e. in very conservative drive cycles.

Cons: adsorption only works at low temps, so the monolith needs to be mounted in the vehicle underbody. It needs to be quite large and contains several times the precious metal mass of a regular three-way catalyst. In other words, it is expensive. Moreover, switching back and forth between lean and slightly rich operation entails a very high application effort for each vehicle model. Not suitable for retrofits.

The biggest problem by far, though, is that sulfur in the fuel will clog up the NOx receptor sites. It takes extended periods of extremely high exhaust gas temperatures to desorb the sulfur compounds. Each such sulfur purge permanently degrades the device. Only with ULSD (<15ppm) or similarly sulfur-free diesel grades is there any chance of meeting the 150,000 mile longevity target set by CARB for all emissions-related equipment.

(b) urea injection involves introducing a consumable - typically a synthetically produce eutectic solution of 325 parts pure urea to 675 parts demineralized water - into the exhaust gas. The heat of the gas causes the liquid to evaporate and undergo precursor reactions that ideally yield only ammonia and carbon dioxide (negligible compared to CO2 from combustion). In the presence of a catalyst, e.g. vanadium oxide, ammonia will preferentially reduce NO and NO2 even if there is free oxygen in the exhaust gas. An additional catalyst at the very end ensures that any ammonia that slips through is converted to harmless nitrogen and water before the gas exits the tailpipe.

Pros: proven to work reliably for many years in stationary power plants and now, in European HDVs. Does not require expensive precious metals and is therefore cheaper than LNTs for large diesel engines (~3.0L and up). Much less sensitive to sulfur contamination. Suitable as a retrofit solution for NOx mitigation.

Cons: high complexity and cost for mobile applications. Consumable addititive must be produced, distributed and actually purchased by vehicle operator - the engine will run just as well without it. Bulk and weight of additive tank, injector and underbody catalyst system. Additive will freeze at -11C, needs to be heated in severe winter weather.

(c) as with all emissions control equipment, modern vehicles must detect possible malfunctions or defeat devices/strategies using on-board diagnostics (OBD). These monitor the signals from various probes for plausibility using mathematial models of roughly what the readings should be given the actuator inputs. If there is a mismatch, either an actuator or a catalyst or a probe is no longer working properly. The engine maintenance light on your dash comes on and you're supposed to bring the vehicle in for service. As a last resort, the OBD can force the engine into a limp-home mode or cut the ignition entirely.

The systems discussed above were long held back by cost and complexity considerations. LNTs, which have been applied to certain stratified GDI engines as well, absolutely need low-sulfur fuel.

Also, the lack of fast, reliable NOx sensors precluded efficient closed-loop control systems. Next-gen urea injection systems will use NH3 sensors instead, but for now it's still all open-loop control.

EPA and CARB also needed a lot of convincing that urea injection systems could be made tamper-proof. The OBD must detect not just low additive volume but also verify that the liquid being injected really is the aformentioned eutectic solution and not just plain water, urine (<5% urea) or something else. Manufacturers / importers must provide a 7/24 hotline so motorists can reach a distribution point for the additive before the run out. The OBD must cut the ignition if they do. Etc. etc., the paranoia level is quite high.

M-B has indicated it will make the additive tank large enough to last for the distance between scheduled maintenance at a dealership. They will not rely on gas stations to stock the product, though that will likely happen once urea injection becomes commonplace in MDVs and HDVs, as it already has in Europe.

jack

If a person avoided the dealership the yearly emissions inspection would catch it.

Some states don't have emissions testing.

Rafael Seidl

@ Jack -

I think they were referring specifically to California, which does have strict smog checks. The states that cannot be bothered to identify grossly polluting gasoline engines probably won't care about diesels with faulty emissions equipment either.

jack

I think they were referring specifically to California

Ah.

The states that cannot be bothered to identify grossly polluting gasoline engines probably won't care about diesels with faulty emissions equipment either.

True, but I think the issue is one of foolproofing emissions, even if there isn't a regular testing regime.

joe blow

California does not currently require smogging for any diesel vehicles. Why? Because diesels typically don't worsen with aging the same way that gas vehicles do. Even with the sale of this T2B5 Mercedes, I havent heard of any change in that status.

Does anyone know different?

joe padula

Please let me know when any diesel will meet PZEV standards, adjusted for increased efficency of the diesel so as not to be unfair. Then I will consider this good news.

joe blow

Joe Padula - rest assured, you'll be the last to know.

Rafael Seidl

@Joe Blow -

the reason is probably more prosaic - there are very few diesel passenger cars in California, so the extra equipment that would be required to test them for emissions would be extremely expensive to install statewide. In Europe, diesel vehicles do have to pass regular emissions checks, just as gasoline vehicles do. This includes an additional test for particulate emissions based on an opacimeter.

The catalysts and DPFs in a modern diesel exhaust system are subject to degradation over time, just as three-way catalysts in gasoline-powered cars are.

@ Joe Padula -

EPA and CARB have never considered the type of engine under the hood. In practice, that has meant setting emissions standards at levels that very few if any diesels could meet, with severe consequences for US oil consumption.

Your proposal is incomplete: just what kind of adjustment did you have in mind? It's fair to demand clean air, but now there is the additional demand for high fuel economy/low CO2 emissions and all of that at an affordable price.

Note that T2B5 / LEV II is considered "clean enough" for new gasoline cars. Why should diesels have to be any better?

Carl

@ Joe Padula -

There was a paper published very recently in the journal Atmospheric Environment (January 2007) which confirms an earlier source apportionment study in 2002 that about 80 percent of the ambient NMHC in the South California Air Basin (SoCAB) is attributed to GASOLINE vehicles (there are virtually no biogenic VOCs in SoCAB - about 1 percent).

This most recent source apportionment study further shows that about 34 percent of that 80 percent (or over 27 percent) is from evaporative emissions from the storage and distribution of gasoline. So even if the entire fleet of gasoline vehicles in SoCAB was "PZEV", there would still be a very significant source of NMHC (in the form of evaporative gasoline emissions - VOCs).

According to EPA (AP-42), diesel fuel is less than 0.4 percent as volatile as gasoline under the same ambient conditions on a mass basis. This source of VOCs could be virtually eliminated with a hypothetical switch to an all-diesel light-duty fleet.

In my opinion, a T2B5 diesel vehicle would have less of an air quality impact than PZEV gasoline vehicles, mainly because of these secondary VOC emissions.

jack

about 80 percent of the ambient NMHC in the South California Air Basin (SoCAB) is attributed to GASOLINE vehicles (there are virtually no biogenic VOCs in SoCAB - about 1 percent).

What percentage of vehicles in the air basin are fueled with gasoline?

So even if the entire fleet of gasoline vehicles in SoCAB was "PZEV", there would still be a very significant source of NMHC (in the form of evaporative gasoline emissions - VOCs).

"PZEVs meet SULEV tailpipe emission standards, have zero evaporative emissions and a 15 year / 150,000 mile warranty. No evaporative emissions means that they have fewer emissions while being driven than a typical gasoline car has while just sitting."

In my opinion, a T2B5 diesel vehicle would have less of an air quality impact than PZEV gasoline vehicles, mainly because of these secondary VOC emissions.

Why don't the people who are in charge of regulating air quality agree with you?

"PZEVs meet SULEV tailpipe emission standards, have zero evaporative emissions and a 15 year / 150,000 mile warranty. No evaporative emissions means that they have fewer emissions while being driven than a typical gasoline car has while just sitting." -- jack

Umm, maybe you missed this part:

This most recent source apportionment study further shows that about 34 percent of that 80 percent (or over 27 percent) is from evaporative emissions from the storage and distribution of gasoline. -- Carl

PZEV only refers to emissions from the car itself. All EPA will do to deal with losses at distribution and refueling is to require recovery-type nozzles and tell you to fill up after 6PM.

Why don't the people who are in charge of regulating air quality agree with you? -- jack

Do you actually know that they don't? Getting regulations passed involves not only what is technically feasible but what is politically possible. There are all sorts of compromises made in these regulations.

Carl

What percentage of vehicles in the air basin are fueled with gasoline?

That 80 percent is from ALL sources, industrial, power plants, biogenic, etc., not just from on-highway sources.

The number of vehicles would not be a good metric anyway. Certainly you’re not equating an 80,000 pound diesel truck “vehicle” with a 3500 pound gasoline car “vehicle”, are you?

"PZEVs meet SULEV tailpipe emission standards, have zero evaporative emissions and a 15 year / 150,000 mile warranty. No evaporative emissions means that they have fewer emissions while being driven than a typical gasoline car has while just sitting."

What’s your point? The VOC emissions to which I’m referring (the 34% VOC emissions) don't come directly from the vehicles themselves. They’re evaporative emissions from gas station storage tanks and bulk storage facilities, evaporative emissions from loading gasoline into a tanker truck, hauling that load of gasoline to a gas station, and off-loading the gasoline at the gas station. Gasoline vehicles create a demand for gasoline, so they’re indirectly responsible for these VOC emissions.

Why don't the people who are in charge of regulating air quality agree with you?

Politics?

jack

Umm, maybe you missed this part:

I saw that. It means that if all the gasoline vehicles went PZEV, NHMC levels would drop by 53% (if the study's numbers are correct). Is a 53% drop a bad thing?

Do you actually know that they don't?

No, I am not yet Omniscient. I'm trying, though.

Getting regulations passed involves not only what is technically feasible but what is politically possible. There are all sorts of compromises made in these regulations.

Using this logic, we could presume anything about anyone's true beliefs and discussing anything would be meaningless. For convenience, we should work with what they say they believe, and this notion that diesels are somehow better for the air than PZEVs seems suspect, at best.

jack

That 80 percent is from ALL sources, industrial, power plants, biogenic, etc., not just from on-highway sources.

"about 80 percent of the ambient NMHC in the South California Air Basin (SoCAB) is attributed to GASOLINE vehicles"

Those two statements are contradictory.

The number of vehicles would not be a good metric anyway. Certainly you’re not equating an 80,000 pound diesel truck “vehicle” with a 3500 pound gasoline car “vehicle”, are you?

I knew you'd pick at that. Here - what percentage of vehicle fuel consumption in the air basin is gasoline?

They’re evaporative emissions from gas station storage tanks and bulk storage facilities, evaporative emissions from loading gasoline into a tanker truck, hauling that load of gasoline to a gas station, and off-loading the gasoline at the gas station. Gasoline vehicles create a demand for gasoline, so they’re indirectly responsible for these VOC emissions.

Great, so we just need to stop consuming gasoline and we'll lick 27% of the NHMC problem in SoCal. No problem.

John

I am a californian and I own a 2007 E 320 BlueTec, V-6. I can't keep up with the tech talk, but I do like the 36.5 mpg I got when I drove my car with 8400 miles on it from Denver to Carlsbad 3 weeks ago. Diesel fuel has something like 30% more energy in it per gallon than gas and much more than ethanol. With 7500 miles on the odo, you can legally register a diesel in ca. I drove hybrids, camry for one, and felt like I had lost my allowance. The E 320 is the right mix of lux and mileage for me, and getting it for $47.9k, about $10k off sticker, suited me just fine. Some people are registering new BlueTecs in AZ, NV etc. and driving them here until the clock hits 7500. This is addressed by the DMV and is indicated as illegal. It's getting done, but if you want to own one, search MB pre-owned or AutoTrader. CA dealers have been trucking in Bluetecs with 7500 miles + and asking as much as $63k, but will take about $57k, depending on actual miles. If you want one, get a certified pre-owned out of state and enjoy the ride home. I only 'needed' to stop for fuel once, but filled the car more often when stopping for food. OK guys, resume your technical discussion, I'll be reading.

jack

John, it's great to see you getting 37 mpg on a 26 mpg and you're very fortunate to have $25,000 extra to toss around so you needn't "settle" for the 34 mpg Camry, which has 1/10 the tailpipe emissions and 2.7 tons less CO2 emissions per year.

It's great that you found a loophole to get around emissions rules in California.

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