TDIClub Forums

TDIClub Forums (http://forums.tdiclub.com/index.php)
-   TDI (Diesel) Emissions (http://forums.tdiclub.com/forumdisplay.php?f=29)
-   -   Relative CO2/NOx emissions vs gasser sister car (http://forums.tdiclub.com/showthread.php?t=487125)

sdean7855 March 8th, 2018 16:15

Relative CO2/NOx emissions vs gasser sister car
 
Can anyone tell me what the CO2 and NOx emissions are for the ALH (A4) vs its gasser sister car is? I get grief about the NOx of my '03 Jetta TDI. I am to understand that CO2 and NOx are inversely related; if you tune for one, the other suffers...but in stock tune what are the numbers. I would like to think that while my Jetta will flunk on NOx, it may be considerably better on the CO2 than its gasser sister.
When the numbers are listed for VWs in the UK, the CO2 is part of the numbers cited...to say nothing of the Brits being able to buy the Polo <sigh>
Here's the current K Polo GTI gasser engine and Polo TDI:
http://sdean.net/images/PoloGTIEngineSpec.jpg http://sdean.net/images/PoloTDIEngineSpec.jpghttp://forums.tdiclub.com/data:image...AASUVORK5CYIIA

MPG figures are in Imperial Gallons, multiply by .8 to get US gallons

TDIMeister March 12th, 2018 14:18

The EPA maintains a database of certification fuel economy and emissions by year and model:

https://www.epa.gov/compliance-and-f...-and-equipment

Your 2003 example archive in a single downloadable ZIP file that covers 1979 thru 2013.

https://www.epa.gov/sites/production...e1979-2013.zip

EPA certification fuel economy is here:
https://www.fueleconomy.gov/feg/download.shtml

TDIMeister March 12th, 2018 17:22

It's important to have an appreciation of magnitudes and impacts of emissions. Without any doubt a diesel vehicle of any vintage since the regulated era will emit more NOx than the closest gasoline equivalent, but there is also also no doubt that a diesel will have higher fuel economy, ie lower CO2 emissions.

But when comparing NOx, we're taking about fractions of a gram per mile, while for CO2, we are comparing magnitudes in the dozens of grams per mile. At what point does, say, 0.2 grams per mile NOx become more important than 20 grams per mile CO2? Or in percentage terms, say an equal percent trade-off between NOx and CO2 for different fueling options, eg 20% more NOx for 20% less CO2? Who makes that judgment and determination? And if both meet the ceiling of the same regulation like Tier2 Bin5, does the absolute value really matter, eg. 0.05 g/mile NOx limit and the diesel just squeaks by and the gasser can do say 0.03 g/mile?

Matt-98AHU March 15th, 2018 14:10

Quote:

Originally Posted by sdean7855 (Post 5388136)
...I am to understand that CO2 and NOx are inversely related; if you tune for one, the other suffers...

That is not quite right. I suppose if you were to "richen" the mixture, thus increasing CO2 due to higher consumption it may also lower NOx some as well, but it would still be much higher than a gas engine with a 3 way catalyst.

The balance of emissions that are targeted are Hydrocarbons (HC) and Carbon MONOxide (CO, no 2) vs NOx. In a gas engine, when you richen the mixture you get more HC and CO, but less NOx. When you lean it out, you reduce HC and CO but increase NOx. That is the inverse relationship where it comes to harmful pollutants. CO2 is not a harmful pollutant nor is it currently regulated here in the U.S. CO2 is regulated in Europe as a way of encouraging the adoption of more fuel efficient vehicles and thus spewing less carbon into the atmosphere.

With that having been said, diesels are EXCEPTIONALLY low producers of HC and CO emissions. As in their levels are so low of those pollutants that they could get away with ZERO emissions equipment and still be far, far under the limit with regards to those two gases. NOx is another story, of course.

Going off the top of my head, when your ALH was new, the federal regulations allowed somewhere around 1.0 g/mi of NOx. The ALH might have beaten that output by a tenth or two. But where the regs also allow 1.0 g/mi of CO, the TDI was a tiny fraction of that.

Actually had an interesting discussion and made a somewhat silly point to bhtooefr last week. I suggested that a modern diesel emits less CO than any gas vehicle. So, he came up with one of the most efficient internal combustion gas setups he could think of: 2017 Prius. And then looked up the numbers for a new Chevy Cruze diesel.

The result? The Prius emits 0.15 g/mi. The Cruze diesel emits 0.10 g/mi. Not much difference, right? There are many other vehicles that emit far more than that, too. The Prius is definitely exceptionally clean.

But just to prove a point about how data is presented can make all the difference in perception, I then came back with all caps: "BREAKING NEWS! 2017 TOYOTA PRIUS EMITS 50% MORE POISONOUS CARBON MONOXIDE THAN DIESEL CHEVY CRUZE!"

Nothing I said was incorrect. Carbon monoxide is quite literally a poison that will kill you in a much more instant sense than NOx. It is absolutely a poison. And the Prius does indeed emit 50% more, which sounds like a lot. But, like tier 2 bin 5 NOx rules that VW was cheating, multiplying a number close to zero is still a very small number... Although, if the numbers are accurate, the cheating TDIs were actually emitting more NOx than your ALH was certified to... So there's that.

But, when you say "Emits 10x the limit of NOx," it's also good to take into consideration that the limit was REDUCED by 10x in the move to tier 2. A BRM code TDI was certified to emit 0.7 g/mi NOx. The "Clean diesels" were only supposed to emit 0.07 g/mi. Literally moved the decimal point on that one.

But, in every other regard, the new clean diesel is definitely cleaner than your ALH. While NOx emissions were probably about the same between the two (if not higher for the cheating new diesels), the new diesels emit ZERO particulates thanks to the particulate filter, less sulfur oxides thanks do a deSOx cat along with the shift to ultra low sulfur diesel which you didn't have when your ALH was new.

Standards have shifted and as far as NOx is concerned, yes, your TDI emits more than most gas engines. But you can also argue, especially if the person knocking you for your vehicle choice drives something not incredibly fuel efficient or new, that yours produces less CO and HC than theirs. And, if you were to hypothetically close yourself in a garage with an engine running, would you choose the old diesel or any gas engine? I'd choose the diesel every time because they naturally produce a tiny fraction of CO of most gas engines and even beat some of the cleanest gas engines out there. And CO is the one gas that is much more of an immediate threat to you staying alive than any other emission.

Not that I recommend locking yourself in a garage with any running vehicle... but the hypothetical still rings true.

An interesting read about NOx is here: https://engineering.berkeley.edu/200...weekend-effect

This is an article by UC Berkeley about a study that was done about NOx and its effects on air quality. For some time there was debate on whether lowering NOx standards were a good idea as there was evidence that suggested lowering NOx made the ratio of NOx to VOCs in the atmosphere just right to maximize production of smog (where NO can be recycled to more harmful NO2 and O3). Gas engines produce more VOCs, although California rules and gas pumps have been setup to basically eliminate most VOCs from internal combustion engine sources along with aerosol cans, so they're convinced VOCs have been reduced to naturally-produced background levels, so they figure instead of allowing NOx go more or less unabated, regulating it down to nearly nothing was the better option. So that's what they did.

Not that it's immediately harmful to breath, as most of diesel's exhaust emissions are NO, not NO2 (regulations lump all nitrogen oxides together...). NO2 you don't want to breath. NO is OK (in fact, your body produces NO to help keep your veins from clogging... seriously. Look up endothelial cells). Although I've also read a study that suggested what comes out of a diesel's tailpipe these days creates more NO2 than they used to because of catalytic converters. Majority of what comes out of the engine is NO, after it's passed through the cat it might be something like 2/3 NO, 1/3 NO2. And if atmospheric conditions are right (very low wind, abundant sun and high temperature and VOCs in the atmosphere--conditions often present in much of California) NO goes through chemical reactions to make NO2 and O3 as mentioned above.

Now, for all the *****ing and moaning some of us do about how difficult the regulations have made life for the diesel world, it turns out the environmentally-minded scientists were indeed right. There have been astounding reductions in photochemical smog in just a few short years in places where diesel traffic is normally heavy. Places like the Port of Oakland and Long Beach. One article I was reading a few months ago made mention of a 70-something % reduction in Oakland in just the first 3 years of the rollout of DPF and effective NOx reduction diesel trucks. That's astounding.

But, this is also why we have state's rights. Hell, there are many counties within California that don't require a biannual smog (but they do require a smog to be performed when selling a vehicle). Some areas don't have a smog problem. And in those areas one could argue it's perfectly fine to remove emissions equipment should they become problematic. But in the densely populated regions that also happen to frequently experience the weather patterns that make smog worse, I cannot condone doing so and of course neither does the government.

Long story short, the regulations do in fact make a very noticeable improvement in air quality for those places that are notoriously problematic. Your tiny diesel is such a small fraction of that, though. And in some ways not buying a new car is better for the environment than frequently buying a new one. Also, you can point out to your friends that NOx is just one small sliver of the whole emissions pie. Your diesel is trading off higher NOx for much lower poisonous CO and HC along with superb fuel economy. That has to count for something. Of course, that is the same reasoning that got Europe into trouble. They then encouraged mass adoption of diesel through tax incentives and air quality got worse because when they began incentivizing diesel, they were not yet clean. No particulate filters and NOx control that is simply not super effective compared to what we have now. But you need to have cumulative effect of mass adoption of the technology for any real pollution like that to happen. In the U.S., the take up rate for all diesels is very low compared to gas engines. So, it's really small potatoes...

I just hope to see improvements in the serviceability, cost and reliability of the emissions components of new diesels. I could go on and on and argue that maybe having a diesel and only drive it in the city is not only a bad idea for pollution but also the vehicle itself. It does seem diesels have more issues when only driven in the city... But they do really shine out on the open highway. I will maintain that diesel is the optimum long distance highway vehicle until battery electrics can do 500-600 miles on a charge and only take a few minutes to recharge to do it again--also providing that the infrastructure is in place and there's not too much demand vs. supply. Until then, there is still a major convenience factor in favor of diesel. Diesel should still be an important technology among others to help us reduce oil consumption until that day comes. And what kind of driving you do most will determine which kind of vehicle best fits what you do. And diesels are definitely not great for the stuck in traffic cycle long term...

TDIMeister March 15th, 2018 17:26

Tl;dr.

The first thing that must be understood is that Diesel and gasoline engine emissions behaviour are completely different as regards to the regulated emissions CO, HC, NOx and PM, plus CO2.

The raw, untreated emissions of gasoline engines will have a profile that looks like the below that is a function of the fuel-air ratio relative to stoichiometric.

http://pics.tdiclub.com/data/4156/SI...ichiometry.png

Of note is that NOx formation takes on a bell-shaped curve that peaks just slightly lean of stoichiometric. But the reason gasoline engines are considered so clean is that 3-way catalyst (3WC or TWC) technology is extremely effective at simultaneously reducing NOx, HC and CO by as much as 97-99%. This, however, requires that AFRs be controlled very tightly close to stoichiometric, so discussions about tuning deviations rich or lean of stoichiometric are mostly irrelevant in the TWC era.

Diesel engine emissions are totally different. Even talking about "rich" mixtures in Diesel are substantially lean of stoichiometric on an overall sense trapped within the cylinder at each cycle, and the amount of emissions formed are governed on very different conditions.

The key difference here is homogeneity, or how well the fuel and air are mixed during the combustion process. In gasoline engines, the mixtures are generally very homogeneous, meaning that the air and fuel ratios are almost uniform throughout the combustion chamber before the moment of ignition. In contrast, a Diesel engine has its fuel only introduced at the moments just before combustion. Mixing takes place as the atomized liquid fuel evaporates and diffuses or "entrains" into the air. Ignition and combustion initiates in a thin interface where the local air-fuel mixture is near stoichiometric (even though the overall or "global" mixture can remain substantially lean of stoichiometric, in the order of 100:1 at idle and low-load conditions). In this region, the emissions profile will actually be similar to the above graph for a gasoline engine at stoichiometric, so high NOx.

Unfortunately, since the Diesel engine still operates globally lean, three-way catalysis is completely ineffective to reduce NOx, so it does not have the low emissions benefit at the tailpipe. Were a Diesel engine to operate at the same nearly exactly stoichiometric conditions as a gasoline engine except employing Diesel fuel and compression ignition, a reformulated TWC can be used and in fact, this has been an area of research. However, you would then lose most of the fuel economy (CO2) benefit that you get from lean-burn.

At the risk of making my own post too verbose, it suffices to stop here to have this base understanding before moving on.

wxman March 15th, 2018 17:49

Very good post, Matt. I agree with almost everything.

The only thing I disagree with is Robert Harley's assertion that the VOC:NOx "ridge line" occurs at 2.4:1 in the Berkeley article you linked. That is far lower than any other source I've seen. Figure 1 in a recent (2016) paper shows the VOC:NOx ridgeline to be about 10:1 ( http://www.atmos.umd.edu/~russ/mazzu...uston_2016.pdf ). I was taught in a grad-level atmospheric chemistry course that the VOC:NOx ridgeline was about 8:1, although that was a long time ago.

It should also be noted that most areas in California are still behaving like they're VOC-limited. For example, according to EPA data, ambient NO2 levels in EPA's "West" region have declined by nearly 17% since 2009 (from 42.4 ppb in 2009 to 35.2 ppb in 2016), but O3 levels have remain nearly stationary (70 ppb in 2009; 69.6 ppb in 2016).

There are also reports that ozone levels in California are actually starting to increase again ( http://www.latimes.com/local/lanow/l...115-story.html ).

I'm not excusing the VW TDI issue, but it still appears anthropogenic VOC emissions are a more important concern than NOx for California and probably most urban areas in the U.S.

turbobrick240 March 15th, 2018 18:22

My guess is the op catching grief over his ALH NOx emissions is 100% attributable to dieselgate. That fiasco has sullied the image of all tdi's in the court of public opinion. Otherwise, it would be the visible particulates that might get a few folks heckles up. I'd just ask those people if they have any idea what the NOx and CO2 emissions associated with building a new car are.

Matt-98AHU March 16th, 2018 18:29

Quote:

Originally Posted by wxman (Post 5390486)
Very good post, Matt. I agree with almost everything.

The only thing I disagree with is Robert Harley's assertion that the VOC:NOx "ridge line" occurs at 2.4:1 in the Berkeley article you linked. That is far lower than any other source I've seen. Figure 1 in a recent (2016) paper shows the VOC:NOx ridgeline to be about 10:1 ( http://www.atmos.umd.edu/~russ/mazzu...uston_2016.pdf ). I was taught in a grad-level atmospheric chemistry course that the VOC:NOx ridgeline was about 8:1, although that was a long time ago.

It should also be noted that most areas in California are still behaving like they're VOC-limited. For example, according to EPA data, ambient NO2 levels in EPA's "West" region have declined by nearly 17% since 2009 (from 42.4 ppb in 2009 to 35.2 ppb in 2016), but O3 levels have remain nearly stationary (70 ppb in 2009; 69.6 ppb in 2016).

There are also reports that ozone levels in California are actually starting to increase again ( http://www.latimes.com/local/lanow/l...115-story.html ).

I'm not excusing the VW TDI issue, but it still appears anthropogenic VOC emissions are a more important concern than NOx for California and probably most urban areas in the U.S.

The levels of ozone are always in flux, too. Although Southern California is definitely more prone to longer dry spells than the North, so it can really build up down there. If it happens to rain, the skies will be very clear for a day or two afterwards! But that's the challenge here, it will go months without significant preciptation. And until about a month ago, LA hadn't seen significant rainfall for about a full year.

I definitely notice a difference depending on weather. When we get more active patterns, wind, rain and the like or even just a strong marine layer in the summer, smog levels are greatly reduced. But when that offshore breeze starts or the wind just stagnates altogether and it gets hot and sunny even at the coast, the smog gets bad.

I have to wonder what the VOC/NOx ratio actually is in L.A. and how much it might eventually be reduced to as more older diesels are taken off the roads and what the ultimate effect will be.

Another take only taking into consideration soot and NOx: https://www.scpr.org/news/2017/03/13...-lost-trust-a/

Certainly the rapid reduction of NOx limits may have been a smidge premature to allow for proper research and development to make the emissions control systems reliable. And clearly truck owners in that article are extra unhappy with the LNG trucks they were heavily incentivized to buy considering the low power and reliability problems. Different engines, but reliability issues nontheless due to forcing people's hands before the technology was fully developed and tested in the real world.

I can only hope that the technology improves in its reliability and effectiveness and that regulators don't go about trying to ban a specific engine technology over the dumb actions of a few. It's a lot to ask for, I know...

Matt-98AHU March 16th, 2018 19:01

Just finished reading the LA Times article you linked to. I like it.

It touched on a lot of what I was talking about how weather plays a big role in smog and the fact that Southern California at least are continually getting more frequent warm, sunny days and less rain in the last several years.

With that in mind, do we now get to say emissions rules have gotten beyond the point of diminishing returns? Should we just halt them where they are? Maybe start doing what Europe does and regulate based on CO2 output as that's the main thing getting the blame for climate change which is contributing to the shift in weather that makes for more frequent hot and sunny days in the LA basin?

Of course if we do that, we should get a LOT more diesels! Although Europe is currently blaming them for all their air quality ills after doing just that... after encouraging their adoption before the implementation of effective NOx treatment and particulate filters. But I digress.

Humanity is a mess and doesn't actually fully know what's going on or what to do about it. Fun, isn't it??

Quote:

Kleeman and other researchers in a 2015 study analyzed air from Los Angeles and found it rich with nitrogen oxides, suggesting future controls need more balance. But he thinks it's unlikely there are large amounts of unaccounted-for emissions driving the increase in ozone.
It's a good article with good information (for once) but it does kind of leave you with more questions than it answers. No one really seems to have the answers on what exactly to do about the situation.

ZippyNH March 16th, 2018 20:56

Also of note...
It has been said that much more co2 is emitted in the production/refining of gasoline....
Since gasoline is often made by "cracking" heaver oils (sometimes seasonally, sometimes due to the raw materials) the energy input and co2 released varries based upon the inputs, but another factor.

turbobrick240 March 16th, 2018 22:06

Quote:

Originally Posted by ZippyNH (Post 5390856)
Also of note...
It has been said that much more co2 is emitted in the production/refining of gasoline....
Since gasoline is often made by "cracking" heaver oils (sometimes seasonally, sometimes due to the raw materials) the energy input and co2 released varries based upon the inputs, but another factor.

It's slightly more according to 2017 GREET data, but the bulk of the CO2 is released from the tailpipe when the fuel is burned. Surprisingly, the default diesel vehicle only has about 3% less total greenhouse gas emissions vs. the default gas vehicle.

wxman March 17th, 2018 08:58

Quote:

Originally Posted by Matt-98AHU (Post 5390841)
...With that in mind, do we now get to say emissions rules have gotten beyond the point of diminishing returns? Should we just halt them where they are? Maybe start doing what Europe does and regulate based on CO2 output as that's the main thing getting the blame for climate change which is contributing to the shift in weather that makes for more frequent hot and sunny days in the LA basin?....

In my opinion, California is beyond the point of diminishing returns with respect to NOx emission reductions and their effect on ambient ozone levels. It appears to me that Southern California in particular is hopelessly VOC limited with respect to ozone formation. Even CARB is projecting the VOC:NOx ratio to be no more than 6:1 by 2035 (it's about 3:1 now). That's still well within the ratio for a VOC-limited regime.

One of the most striking examples of the NOx-O3 relationship in a strongly VOC-limited regime is a multi-year study done in Israel which empirically showed that on days with virtually no anthropogenic NOx emissions (during a religious holiday - "Day of Atonment"; 83%-98% decrease in ambient levels), ozone levels INCREASED by 8 ppbv at urban core, and only decreased by 5 ppbv downwind. Nighttime ozone levels rose by 20 ppbv at urban sites and 30 ppbv downwind (Ilan Levy, "A national day with near zero emissions and its effect on primary and secondary pollutants." Atmospheric Environment, Volume 77, October 2013, Pages 202-212, http://www.sciencedirect.com/science...52231013003488 (abstract)).

wxman March 17th, 2018 11:48

Also, on the CO2 emissions front, Europe has seen its first rise in average CO2 emissions from the passenger car fleet in a decade, thanks in part to the decreased sales of diesel vehicles and the increased sale of petrol vehicles resulting from the proposed diesel bans in many cities there.


http://www.greencarcongress.com/2018...0306-jato.html

turbobrick240 March 17th, 2018 13:21

Quote:

Originally Posted by wxman (Post 5390930)
In my opinion, California is beyond the point of diminishing returns with respect to NOx emission reductions and their effect on ambient ozone levels. It appears to me that Southern California in particular is hopelessly VOC limited with respect to ozone formation. Even CARB is projecting the VOC:NOx ratio to be no more than 6:1 by 2035 (it's about 3:1 now). That's still well within the ratio for a VOC-limited regime.
One of the most striking examples of the NOx-O3 relationship in a strongly VOC-limited regime is a multi-year study done in Israel which empirically showed that on days with virtually no anthropogenic NOx emissions (during a religious holiday - "Day of Atonment"; 83%-98% decrease in ambient levels), ozone levels INCREASED by 8 ppbv at urban core, and only decreased by 5 ppbv downwind. Nighttime ozone levels rose by 20 ppbv at urban sites and 30 ppbv downwind (Ilan Levy, "A national day with near zero emissions and its effect on primary and secondary pollutants." Atmospheric Environment, Volume 77, October 2013, Pages 202-212, http://www.sciencedirect.com/science...52231013003488 (abstract)).


Hasn't the "weekend effect" where NOx reductions actually increase ozone formation disappeared over most of US cities, and been dramatically reduced in the LA air basin in recent years? I think the dirth of biogenic VOC's from vegetation is largely responsible for the weekend effect in Israel. Seems like the solution in So Cal is to plant more trees and reduce all ICE emissions. With increased EV adoption in California, we may see the weekend effect disappear there almost entirely.

wxman March 17th, 2018 13:56

Quote:

Originally Posted by turbobrick240 (Post 5391003)
Hasn't the "weekend effect" where NOx reductions actually increase ozone formation disappeared over most of US cities, and been dramatically reduced in the LA air basin in recent years? I think the dirth of biogenic VOC's from vegetation is largely responsible for the weekend effect in Israel. Seems like the solution in So Cal is to plant more trees and reduce all ICE emissions. With increased EV adoption in California, we may see the weekend effect disappear there almost entirely.

The weekend effect has become less pronounced; it now appears the weekday/weekend levels are about the same (as opposed to actually increasing).

I think you're correct about the dirth of biogenic VOCs in Israel as the reason for the extreme VOC-limited regime there, but doesn't Israel and Southern California have about the same climate ("Mediterranean")?

The fact remains that ambient NO2 levels have dropped considerably in Southern California...


https://www3.epa.gov/region9/air/trends/pdfs/NO2.pdf


...but much of that area remains in "extreme" non-attainment with the ozone NAAQS...


https://www3.epa.gov/airquality/gree...ap8hr_2008.jpg


There's also the issue that Southern California appears to have relatively high biogenic NOx emissions...


http://webpages.charter.net/lmarz/muncie/NAAQS_NO.png

(Oikawa, P. Y. et al. “Unusually high soil nitrogen oxide emissions influence air quality in a high-temperature agricultural region.” Nat. Commun. 6:8753 doi: 10.1038/ncomms9753 (2015)).


All times are GMT -7. The time now is 05:16.

Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Copyright - TDIClub Online LTD - 2017

Page generated in 0.10592 seconds with 7 queries
[Output: 74.38 Kb. compressed to 73.45 Kb. by saving 0.93 Kb. (1.25%)]