First Drive: 2008 Volkswagen Jetta TDI - Previews

Waldek Walrus

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May 15, 2006
Location
Central Pennsylvania
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2006 Beetle TDI
Richer Mixture??

OK, Its promising that VW is planning on offering a 2008 diesel in the US. On the other hand, how much is this "hotter" exhaust cycle to burn off the NOx and particulates in the trap going to cost in fuel economy? At one point it was postulated that it would cost half of the fuel saved by going diesel to burn off the trap - that is enough to kill off the economic and greenhouse gas advantage of the diesel. Worse, this cycle is "imperceptible to the driver" so how do you know if it cycles too much, using even MORE fuel. I think I'm glad I got a 2006.
 

TDIDerek

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Sep 9, 2006
Location
Grantsville, MD
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None Yet
Im glad that its going to have some more power. I chose to wait it out until the 2008 model. One thing that the article fails to mention is fuel economy, when are we going to get some estimates on this thing?
 

oilhammer

Certified Volkswagen Nut & Vendor
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Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
They don't say what engine exactly it is, but by the sounds of it being more HP and less TQ than the B5's 2.0L TDI, I wonder if it is the multivalve version?

I think the PD's actually run a periodic richer mixture for the same reason, as well as MB's current CDIs, but I am not sure. TDImeister could clarify that I'm sure...;)
 

SilverGhost

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Mar 25, 2005
Location
Back in So Flo - St Lucie
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'05 Golf - totaled :(, wife's '13 Beetle - buy back, TDIless
MPG on 08's

TDIDerek said:
Im glad that its going to have some more power. I chose to wait it out until the 2008 model. One thing that the article fails to mention is fuel economy, when are we going to get some estimates on this thing?
I think when someone on here saw the car in Michigan last year the VW reps were saying 60mpg highway and 45mpg city. Sounds absurd considering what the outgoing model gets, but we don't know what all else was done to this engine to make it 50 state legal.

I don't have any new info on rated mpg though.:(

Jason
 

Tahna Los

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Toronto
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Waldek Walrus said:
OK, Its promising that VW is planning on offering a 2008 diesel in the US. On the other hand, how much is this "hotter" exhaust cycle to burn off the NOx and particulates in the trap going to cost in fuel economy? At one point it was postulated that it would cost half of the fuel saved by going diesel to burn off the trap - that is enough to kill off the economic and greenhouse gas advantage of the diesel. Worse, this cycle is "imperceptible to the driver" so how do you know if it cycles too much, using even MORE fuel. I think I'm glad I got a 2006.
Richer probably in terms of more oxygen than fuel, I'm betting. You put more fuel than oxygen and you get an incomplete combustion, which results in all that particulate matter. Put the other way around and you get a blast that eats oxygen for breakfast.

Which begs the question: why don't they have this richer combustion on all levels at all times so that they don't have to have a filter? My only guess is that the engine cannot take consistently high temperatures like that (wears down the engine quicker), so it can only do it in bursts.
 

LVPAJetta

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Northern, NJ
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GSW, 2015, Silver, 6-spd
Going back to college and an engine design class I had (gasser only, sorry) they run engines a little rich as a trade off between NOx emissions and hydrocarbons. The lean mix w/ higher temps led to more NOx. While I don't know the combustion chemistry of the diesel engine (higher pressures do funny things I'm sure), it's possible that they run things a little fuel rich for the same reason.
 

RabbitGTI

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Jul 20, 1997
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Wisconsin
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B4 Passat Sedan
Anyone know if a cutaway version of that motor is making the rounds of the Autoshows? If so, can anyone post photos?
 

Kenbob

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Joined
Sep 7, 2000
Location
God's country (Texas)
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2010 Audi TDI
I'd like to clarify something on this because I keep seeing people make confusing statements. Diesel engines cannot run 'rich' like a gasoline engine. Gasoline engines are throttled and ideally run a stoichiometric ratio of fuel to air (14.7:1). This is controlled by how much air is allowed into the cylinder and how much fuel is injected (or sucked in through a carburator). Therefore gasoline engines can run rich or lean depending on how the computer controls things.

Diesel engines are unthrottled and always have excess air. They never run stoichiometric. At max power (what we call 'wide open throttle'), the fuel/air ration is still probably 20:1. At idle it may be 100:1 and some value between the two at cruise. Power in a diesel is controlled completely by how much fuel is injected. If you run 'richer', you produce more power. More power makes the car go faster, unless you apply the brakes and convert it to heat. More air is added with turbocharging to allow even more fuel to be injected without smoke, but the richest ratio doesn't change significantly.

The only variable is injection timing which effects the efficiency of the combustion and can result in more unburnt hydrocarbons in the exhaust. That is the only way you can inject more fuel into the combustion chamber without producing more power, and the timing effect is small within the normal operating parameters of the engine.
 

Lug_Nut

TDIClub Enthusiast, Pre-Forum Veteran Member
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Sterling, Massachusetts. USA
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idi: 1988 Bolens DGT1700H, the other oil burner: 1967 Saab Sonett II two stroke
Thanks Ken, Saved me a bunch of typing.
I hope the burn-off doesn't mean a reversion to the 96 B4's supplemental injector for the catalytic converter...
 

PlaneCrazy

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Province of Quebec, Canada
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Gone...
Kenbob speak truth.

However, I would like to point out another technology with gas engines. I will soon be taking delivery of a Passat wagon with the 2.0T FSI engine. The FSI stands for "fuel stratified injection". The beauty of this technology is that a gasser behaves more like a diesel; no longer is a stoichiometric ratio required for combustion. The intake valve ingests pure air like a diesel and the injector injects fuel as required to get the job done, as in a diesel. Compression ratio is less though, and spark ignition is still used.

Of course gasoline needs a stoichiometric ratio to explode when ignited. However the FSI engine works by having an overall air/fuel ratio that is non-stoichiometric (lean), but having stratified areas in the cylinder where there are localized stoichiometric ratios, so it's a "lean-burn" engine. When full power is required, the engine runs with a stoichiometric ratio, but in highway cruise, in max. lean burn mode for excellent efficiency.

Apparently sulphur content in our gasoline is an issue and does not allow full FSI benefits, but when this is addressed (where have we heard this before!) the ECU can be remapped to run in lean-burn mode. Already the 2.0T turbo gets fairly decent highway economy: in the Passat, about 6.7 L/100 km on the highway; I've seen numbers from France that suggest 6.3 in the lighter Jetta (rated a bit higher in N. America).

To put it into context, the closest TDI match in performance in N. America would be the B5.5 Passat (134 hp/247 lb-ft vs 200 hp and 207 lb-ft), rated at 5.7 on the highway. If you think about it, given that diesel contains about 10% more energy than gasoline, the gas engine should have a rating, all other things being equal (weight, etc) of about 6.3 L/100 km. However even FSI is a little less efficient, at 6.7.

So good efficient gas engine design is getting close to diesel in efficiency. Still a few drawbacks though: need premium, and you're still carrying around 70 liters or so of an explosive liquid in your back end, and of course gas is less efficient to refine than diesel.

Still, one wonders if the future isn't in more efficient gas and diesel engine design, NOT hybrids. Take VWs TSI engine, 170 hp an rated at 5.9 L/100 km on the highway, out of just 1.4 liters of displacement. Without the hassles of hybrids (battery packs, underpowered gas engines when the batteries run down, etc).

It's odd how VW has some great gasser designs (2.0T, normally aspirated FSI, TSI), but here in N. America, we only get the 2.0T, the others being the piggish 2.5, the awfully outdated 2.Slow (still sold in Canada in the "City" models), and the "who the heck needs 280 hp in a midsize" 3.6 (although it is FSI).

If you ask me, apart from the Touareg, VWs only need the 100 and 140 hp TDIs, and the 2.0 FSI (normally-aspirated, 150 hp), 1.4 TSI (170 hp) and 2.0T (200 hp) for more than adequate motivation in the Golf/Jetta/Passat/NB/Eos lineup. Actually in Europe the base engine in the Passat is a 1.6L, 102-hp gasser...slow but it can still cruise at European speeds...we in N. America need to rethink our love of high displacement inefficient engines.
 

moondawg

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Oct 25, 2003
Location
Columbus, IN
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2001 Galactic Blue Jetta
Lug_Nut said:
Thanks Ken, Saved me a bunch of typing.
I hope the burn-off doesn't mean a reversion to the 96 B4's supplemental injector for the catalytic converter...
You won't need it, because the Common Rail system can be made to fire during the exhaust stroke, which does the same thing.

And yes, they will likely be injecting some fuel into the exhaust.

The DPF(Diesel Particulate Filter) systems used to trap soot work by storing all of the little soot particles and burning them off all at once. These systems require ALOT of heat to completely burn the soot. To get this heat, many systems utilize a DOC(Diesel Oxidation Catalyst) to help burn fuel injected into the exhaust stream. In order to help this process along, most systems use some sort of intake or exhaust throttle to provide some extra load on the engine to generat more heat.

So, the process goes generally like this:

1. Measure pressure across the DPF, notice that it is getting clogged with soot.

2. Tell engine to go into "generate more heat" mode.

3. Once exhast temps are high enough, start injecting fuel.

4. Hot exhaust and fuel hit DOC, get even hotter.

5. Resulting hot gasses burn off soot.

6. Measure pressure across the DPF, notice that filter is clean. Stop process and wait for soot to build up again.

Wash, rinse, repeat.

moondawg
 

MrMopar

Top Post Dawg
Joined
Mar 1, 2003
Location
Bloomington, IL
TDI
none
Waldek Walrus said:
OK, Its promising that VW is planning on offering a 2008 diesel in the US. On the other hand, how much is this "hotter" exhaust cycle to burn off the NOx and particulates in the trap going to cost in fuel economy? At one point it was postulated that it would cost half of the fuel saved by going diesel to burn off the trap - that is enough to kill off the economic and greenhouse gas advantage of the diesel. Worse, this cycle is "imperceptible to the driver" so how do you know if it cycles too much, using even MORE fuel. I think I'm glad I got a 2006.
The new engine will probably monitor back pressure of the exhaust stream to judge when it is time to rejuvenate the particulate filter.

If that be the case, easy mod for higher fuel economy:
Step 1: Cut DPF out of the exhaust
Step 2: Install straight pipe replacement
Step 3: Save on fuel costs, maybe more HP from less back pressure
 

weedeater

Top Post Dawg
Joined
Mar 17, 2001
Location
Reston, VA
TDI
Jetta, 2001, Baltic Green
I would guess it would be based more on time, running how long at what RPM. Easier for the ECU to measure.
 

Waldek Walrus

Veteran Member
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May 15, 2006
Location
Central Pennsylvania
TDI
2006 Beetle TDI
Fifth Injector...

Lug_Nut and moondawg both get at what I am afraid of - extra fuel getting dumped into the exhaust to burn off the trap. The original article talked of rich mixture which is a gasser concept and doesn't fit diesel - but that extra injector idea has been tried (and failed). Where I live there is an emission inspection that would catch any effort to by pass the system; so as tempting as that idea is, it is out of the question. So much for 800 mile club...:eek:
 

Kenbob

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Location
God's country (Texas)
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2010 Audi TDI
Ah, so many good points brought up. As PlaneCrazy said, direct injection gasoline engines can run in a very lean mode. They are still throttled though, and the pumping losses probably account for a large part of the difference between the absolute efficiency (fuel energy content included) of the spark ignition and diesel cycles. FSI still relies on throttling airflow for power and diesel doesn't.

As Moondawg said, injection during the exhaust stroke would work for the catalyst light-off. I hadn't considered that as I was still in injection pump thinking mode. I bet that's how they do it.
 

darkscout

Grammar Scout
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Location
Michigan
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2003 Golf
Waldek Walrus said:
Lug_Nut and moondawg both get at what I am afraid of - extra fuel getting dumped into the exhaust to burn off the trap.
That's what every on high way truck manufacturer is doing (that I've seen). Cummins and DDC are using dosing, Caterpillar is using their own "CRS" system to elevate exhaust temps.

Is there a scheduled ash removal period? Burned oil creates ash. The ash doesn't burn off in the DPF and accumulates, which means that after time it has to be removed.

It's a nightmare to say the least.
 

Mike_M

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Joined
Sep 23, 2003
Location
Phoenix, AZ
TDI
Black 2002 Jetta GLS
I guess I really will be running my '02 up to a million miles before I get rid of it. Then I'll try to find another one. :D

All the idiocy they're going thru to over-regulate NOx is gradually ruining the chief benefit of these cars...fuel economy, less maintenance, and less greenhouse gas (CO & HC) emissions.

Or, said another way, more s#!t to break.
 

MrMopar

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Location
Bloomington, IL
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none
darkscout said:
Is there a scheduled ash removal period? Burned oil creates ash. The ash doesn't burn off in the DPF and accumulates, which means that after time it has to be removed.
From what I understand, these new pollution controls are requiring a good amount of progress to be made with lubrication oils just for this reason. Even in the last 15 years, enough changes have been made to gasoline auto emissions systems to the point where using diesel rated engine oil is not too good for the catalyst due to products left from oil burning.

I used to work at a Wal-Mart oil change place for 3 years while in college, so typical me tried to learn as much as possible about subjects that maybe no one cared about. I tried to absorb as much information about oil products and chemistry so that I could make the best recommendations to the customers who actually cared what I had to say.

I'm fuzzy about some oil chemistry, but more than one conversation with long-term mechanics came with the suggestion to use diesel rated engine oil in gasoline engines for the longest engine life with fossil oils. The consensus was that GF-3 rated oils (all modern 10w30 and 5w30 oils) had to cut back on anti-wear additives and TBN additives so that when oil was consumed in combustion, the ash remanents wouldn't contaminate the catalyst. Since diesel oils (my standard for my beaters, Rotella-T 5w40) didn't have to worry about catalyst contamination, they could still have the anti-wear additives for longer engine life and longer oil change intervals.

I've read some documentation about how the new DPF traps on semi-trucks are going to need full cleaning overhauls on a schedule of something like every 400,000 miles or so. Obviously the trucking industry is not thrilled with yet another expense. I think that fuel consumption for the semis wasn't a problem, because the engines are run at a heavy enough throttle most of the time to not need a regeneration cycle. But I can still see why they'd be fighting regulations to retrofit DPF to old semi-trucks.
 

lbhskier37

Veteran Member
Joined
Jun 27, 2006
Location
Appleton, WI
TDI
none yet (2008 soon)
Waldek Walrus said:
Lug_Nut and moondawg both get at what I am afraid of - extra fuel getting dumped into the exhaust to burn off the trap. The original article talked of rich mixture which is a gasser concept and doesn't fit diesel - but that extra injector idea has been tried (and failed). Where I live there is an emission inspection that would catch any effort to by pass the system; so as tempting as that idea is, it is out of the question. So much for 800 mile club...:eek:
I wouldn't think this extra late injection is going to cause a significant increase in fuel consumption. All 2007 heavy trucks are using the same thing to regenerate their particulate filter, and in all the articles I have read, equipment manufactures are claiming fuel consumption is down over 2006 models. This extra injection doesn't happen every cycle, and it doesnt have to be very big, it is basically just sending a big flame out the exhaust port whenever the DPF needs to be regenerated. This technology is in every 2007 onroad diesel engine and has been in the works for years, if VW did their homework this should be pretty mature by spring '08. By then the trucking and equipment industry will have over a year and millions of miles on the stuff.
 

darkscout

Grammar Scout
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May 28, 2006
Location
Michigan
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2003 Golf
All the new 2007 trucks have a suggested engine oil of CJ-4 for this reason, however there is still blow by and oil still gets burned.

The EPA minimum requirement for a DPF cleaning is 150k. Everyone has different technology. Some is pretty much a big vacuum, others is a chemical. And 400k is *very* optimistic.

As far as:
MrMopar said:
I think that fuel consumption for the semis wasn't a problem, because the engines are run at a heavy enough throttle most of the time to not need a regeneration cycle. But I can still see why they'd be fighting regulations to retrofit DPF to old semi-trucks.
That's what I thought when I first started working here. Semis are just the beginning of the story.

Garbage trucks, firetrucks, RV, Cement Mixers, Dump trucks, (ad infinitum Vocational Trucks), local delivery trucks, UPS/FedEx, School Bus, City buses...

In addition, some Semi trucks see up to 40%! idle. Idle waiting for the docks, Idle over night, Idle at home, some idle all weekend. Fleet owners are pushing for APUs but they're not mandatory.

When I worked at a previous company that did a case study to see how Garbage trucks were used. At some times it was 100% Throttle and 20% brake. Imagine how much soot you'd build up in these DPFs. Some of these vehicles never see more than 15 MPH. Follow a City bus around. Every time it takes off what does it do? All of that has to be trapped now.

You have to figure out how to burn off *all* of that soot plus you have to deal with the ash afterwards.
 
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darkscout

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Michigan
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lbhskier37 said:
I wouldn't think this extra late injection is going to cause a significant increase in fuel consumption. All 2007 heavy trucks are using the same thing to regenerate their particulate filter, and in all the articles I have read, equipment manufactures are claiming fuel consumption is down over 2006 models. This extra injection doesn't happen every cycle, and it doesnt have to be very big, it is basically just sending a big flame out the exhaust port whenever the DPF needs to be regenerated. This technology is in every 2007 onroad diesel engine and has been in the works for years, if VW did their homework this should be pretty mature by spring '08. By then the trucking and equipment industry will have over a year and millions of miles on the stuff.
The difference is most heavy trucks have an additional injector *after* the turbo. I wonder what this flame is going to do to turbo seals and such.
 

tdipower4me

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latham ny
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03 jetta
hmm.... so in 2008 when the new tdi's arrive, will it have to meet emmissions when you get the anual inspection like the gassers? or will it be like now in nys with tdi's? if you won't have to pass emmissions, then you can just gut all the restrictive **** and have rocketchip program it so no cel's
 

moondawg

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weedeater said:
I would guess it would be based more on time, running how long at what RPM. Easier for the ECU to measure.
You'd think so, but no. The amount of soot the engine produces varies ALOT, especially during transient conditions.... a simple time model, even if the engine is run at steady-state, can be wildly inaccurate.

Measuring the pressure across the filter is the only reliable way to do this at this point.

moondawg
 

DickSilver

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Present diesel design, as in my 2004 Passat TDI, uses a technique to make it look like it is running stochiometric to a hair "rich" in order to cut NOx emissions. NOx is created in a "normal" (uncontrolled) diesel because there is typically lots of leftover O2 after combustion. So in the PD engine, VW senses the O2 content in the exhaust and opens the EGR valve enough to put sufficient exhaust gases, which are lower in O2, back in with the intake air.

For those of us who have had to put up with this system, it brings another and very irritating side effect: particulate carbon in the exhaust mixes with oil mist from the crankcase vent, creating thick sludge that gradually clogs the intake manifold. (Which I have dealt with by installing a really good CCV filter.)
 
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