Naked Science Forum
Life Sciences => The Environment => Topic started by: peppercorn on 30/11/2010 17:42:52
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IIRC, at present the parts-per-million counts for CO, HCs and NOx in exhaust emissions are legislated to remain below maximum limits (in normal driving).
But, due to catalytic-converters being ineffective during their warm-up period, the PPM exempts a certain amount of running time. Also, I assume that cold weather conditions, etc can lengthen this period further.
In a similar way to the take up of the combined-cycle in measuring fuel consumption, would it not be logical to develop a similar approach to particulate pollutants?
NB: I'm not saying completely remove an upper limit for instantaneous PPM counts (Big puffs of black smoke from diesels is not good!), but it could be backed off slightly in favour of a better overall full-cycle average.
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I think that the whole pollution question needs to be evaluated by an independent scientific body that would consider both vehicle lifetime and embodied energy and pollution for construction (e.g. what does it take to make a catalytic converter). The harm from each of the pollutants should be considered when setting relative and absolute limits.
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I agree that the vehicle emissions need to be re-evaluated, and it should be more comprehensive than just targeting the lowest possible concentration.
There are issues of cumulative concentration of pollutants, especially in urban areas. Thus, while a Catalytic Converter or similar device may be energy intensive to manufacture, it may be effective with displacing CO and NOx out of the urban areas. Perhaps it isn't a big issue for Rural residents, but still potentially an issue for suburbanites and those living in satellite communities.
However, other issues should also be considered including whether the emissions equipment adversely affect fuel efficiency including the burnoff cycles with the DPF. Of course, noting that efficient emissions often uses a combination of excellent engine tuning plus the devices such as a CAT.
Also, rather than just basing everything on relative concentration, the standards should also take into account overall output. Thus, a Diesel Hummer wouldn't be favored over a Diesel Smart Car due to emission concentration while the Smart puts out only a fraction of the total emissions of the Hummer.
More effort needs to be put into merging global emission and Safety standards.
It is ludicrous that it is illegal for an American to buy or import European cars that are built to excellent standards, and get over 70 MPG.
As far as maintenance on aging vehicles. It can become astronomically expensive to repair the emission system on a 20+ yr old car that only gets driven a few thousand miles a year. St. Louis has exempt all pre-ODB II vehicles which is a step forward. But, the 20+ yr old vehicles are the minority of the vehicles on the road, and they usually get driven less than the newer vehicles. Standards should be made not to put undue hardship on the owners. One might have to look at it, but I don't believe the older vehicles are a major contribution to the overall emissions output.
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Also, rather than just basing everything on relative concentration, the standards should also take into account overall output. Thus, a Diesel Hummer wouldn't be favored over a Diesel Smart Car due to emission concentration while the Smart puts out only a fraction of the total emissions of the Hummer.
Agreed. This is a good point indeed, if PPM is based on overall consumption (more specifically air/fuel through-put), then there is (relatively) much more room for manoeuvre for large displacement vehicles than for small. This seems counter to where we should be heading.
As far as maintenance on aging vehicles. It can become astronomically expensive to repair the emission system on a 20+ yr old car that only gets driven a few thousand miles a year. St. Louis has exempt all pre-ODB II vehicles which is a step forward. But, the 20+ yr old vehicles are the minority of the vehicles on the road, and they usually get driven less than the newer vehicles.
I should say that I suspect that the majority of emissions-linked service costs are roughly dependent on miles driven, so the costs to the owner are fair. However I do agree (very strongly - having a classic motor myself) that encouraging drivers to, blindly, move to replace their 10+ year old cars, is not always the best thing it terms of carbon.
In the UK older vehicles have been except from emission testing since its introduction (beyond a visual 'black-smoke' check) and this seems a fair balance. I have heard that emission tests may be phased out altogether, but am not sure of the thinking behind this (if true - It won't change my MOT test either way).
I do think aspects like DPF burn-off cycles should be factored in as part of a proposed full driving-cycle calculation for particulate count. I don't suppose these cycles are a particularly regular occurrence (unless some engine component is faulty), but it does seem bazaar that current legislation is only concerned with normal running conditions (not warm-up or purge cycles) in producing the figures.
I believe their are also separate rules on commercial vehicles (even those used for purely private motorists) w.r.t. PPM and CO2 counts - Again illogical IMO. Especially since, for say a small van, the entire drive-train is identical to the factory's cars.
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Heh :)
Stop using cars
But.
Let the bikes be :)
The 'Real ones' of course, not those black ugly ones..
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Big black ugly ones I meant..
heh.
.. Censured at last :)
Tells you what bike he drives :)
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peppercorn:
In this thread you are questioning parts per million (PPM) as a valid measure of auto exhaust pollution, which I also think is not just invalid, but just plain stupid. However, on your other post in Physical> Tech> "Do our cars really need CATs" (catalytic converters) you were talking about the regulations as specifying grams of pollutants per mile GPM). PPM is a ratio such that a small engine that measures the same as a large engine, would actually be releasing much less pollution. GPM is an absolute measure where engines would be fairly rated on the basis of the total pollution they release. Please explain.
Steve
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...Please explain.
Steve
Would that I could Steve [:D]
I guess I had better go check my sources!
Can someone confirm what the -US- EPA uses in their standards?
GPM is obviously the better descriptor, but I had thought I'd also read limits in PPM. [???]
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Here is a chart of Diesel Fuel Standard Changes over the last fuel years.
Both EPA, and European Union.
(posted on a Ford website earlier, I think).
http://www.slideshare.net/FordMotorCompany/diesel-forum-presentation
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi50.tinypic.com%2F3582bkw.png&hash=d93a3f37c9e7a48a83eceb3d37490bf4)
Height of the bar is NOx.
Width of the bar is Particulate Matter.
They are listing them in g/HP-hr or g/KW-hr
So, this seems to be based on the instantaneous HP output of the engine, which may actually be somewhat fair, although it does set a very low bar for the low HP vehicles, especially those running with a small engine near max HP output.
Oh... Man... Now my head is spinning [::)][:o] [B)] [xx(]
I'm pretty sure my previous EPA testing reports were all in PPM. However, the actual "requirements" are essentially impossible to track down so perhaps they are being dynamically calculated for each vehicle. So that if one went to a mechanic, the ppm would be easy enough for the mechanic to measure. I'll see if I can find some old reports later.
Previous tests were always done on a dynamo rollers... but the last time I had my car tested, it was done only at idle. I've never had a car that was newer than 1991 tested though. Perhaps things have changed.
It looks like there are standards in:gm/HP-hr or gm/KW-hr
As well as gm/mile
Cars are also broken down into the categories:Low Emission Vehicles
Ultra Low Emission Vehicles
Super Low Emission Vehicles
Partial Zero Emission Vehicle
Advanced Technology Partial Zero Emission Vehicle
Zero Emission Vehicles (Electric)
With all of those categories, they have weights of< 8500 lbs
8501 to 10,000 lbs
10,000 to 14,000 lbs
(and I assume heavier)
They also seem to have values for a "Durability Basis" of vehicle miles with slightly more lenient values for cars over 120,000 miles:50,000 miles
120,000 miles
150,000 miles
Anyway, here are all the California Testing Standards which seem to be the basis for most of the EPA SMOG testing, at least in Oregon too.
http://www.arb.ca.gov/msprog/levprog/cleandoc/cleancompletelevregsasof8-14-04.pdf
Here is a book on Google Books, "Air Pollution for Motor Vehicles"
Chapter 1 summarizes the emission standards by country.
http://books.google.com/books?id=Hqsyv_KD0lgC&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false
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I am also frustrated by trying to figure this out. The fact that this should not be difficult in contrast to the fact that it is, is the reason I have a very suspicious attitude about US pollution standards and the potential nefarious lobbyist input into our laws. Grams/hp or KWh is just a way to scale a small, lightweight car as equal to a giant, heavy one, when actually the larger car is releasing many times the amount of actual pollution.
The people who want to have their monster car should have to pay for the extra damage to all the rest of us they cause.
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The efficiency of the engine tallies quite well with the ppm of pollutants in the exhaust.*
Since they are seeking to improve efficiency that's what they measure.
The fact is that mopeds and 4by4s simply aren't the same thing. You cannot directly compare miles per gallon for the two.
Don't forget that the gas guzzlers already pay more tax because they use more fuel (which is heavily taxed).
* an ideal, lean-burn engine would produce about 140000 ppm CO2, 0 ppm NOx, 0ppm CO, 0ppm hydrocarbons and zero ppm SOx no matter whether it was diesel or gasoline and whatever the engine capacity.
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The efficiency of the engine tallies quite well with the ppm of pollutants in the exhaust.*
Since they are seeking to improve efficiency that's what they measure.
The fact is that mopeds and 4by4s simply aren't the same thing. You cannot directly compare miles per gallon for the two.
Don't forget that the gas guzzlers already pay more tax because they use more fuel (which is heavily taxed).
* an ideal, lean-burn engine would produce about 140000 ppm CO2, 0 ppm NOx, 0ppm CO, 0ppm hydrocarbons and zero ppm SOx no matter whether it was diesel or gasoline and whatever the engine capacity.
I was under the impression that keeping NOx down was the hardest thing in lean-burn due to peak cylinder temps. A lean-burn with hybrid could potentially only need a single 'one-way' cat.... ?
I think that, although you're right about comparing mopeds with 4x4s, it's no bad thing to add a further incentive to downsize displacement (providing it's a fair incentive going back to my OP). Currently the US & others still have very lenient taxation for 'gas' and, although (in a world of only rational consumers) tax at the pump is by far the fairest, I think other ways (inc. legislating at manufacture) are required for fast and effective change.
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I didn't say that an ideal lean burn engine (or anything close to it) exists ;-) .
I worry about the idea that only rich people will be able to afford to poison poor people. However, tax at the pump sees to be the least bad option.
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To clarify what I am saying- Percent pollution doesn't mean squat, it is the amount that counts and this is what should be taxed whether it be a moped or a large truck. This is the only way to represent the real cost of using fossil fuels.
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Currently the US & others still have very lenient taxation for 'gas'
A typical Eurocentric view IMHO. Tax the heck out of it, and if that doesn't work, tax it even more [;D]
Considering the UK is a net exporter of oil, I'm a bit surprised there hasn't been a blinking revolution over the ridiculous amount of tax that's levied on petrol.
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Geezer:
My view is very definitely of the US. There are some in my country who think, like (hopefully decreasing numbers of) economists, that such things as water depletion, pollution damage, resource depletion, and any other cost to the commons should be ignored. These costs are called "externalities" by old time economists, but this practice cannot continue. This rapacious attitude allows large business to do major cost shifting to all the rest of us for their own benefit. I am very patriotic and am very concerned about this anti American attitude.
Steve
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Steve:
Who said anything about encouraging the depletion of natural resources? All I said was taxation is not a very effective tool. It's not working very well in your home state (I've lived there and in Europe BTW) which is about to go bust despite (or perhaps because of) the enormous burden it places on its productive citizens, which is not unlike the typical European model.
Geezer
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This is going a bit 'off topic', don't ya think guys?
The point is taxation (of whatever flavour or mix) doesn't appear to work alone.
Redefining the air-quality and emissions laws should ensure that car manufactures are 'encouraged' to make and sell cars with efficient (and non-bloated) engines without the need of complex bolt-on (hidden-) tax incentives (that just cause bureaucratic waste).
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This is going a bit 'off topic', don't ya think guys?
Sheesh! You started it with the tax stuff [;D] [;D]
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I don't really care about how important realities are dealt with. What I do care about is resource depletion and environmental degradation. I am especially concerned that nobody wishes to put a cost on using the rapidly diminishing commons. We are approaching another tragedy of the commons and problems with automobile emissions and fuel usage are a sizable component. (Geezer, my taxes are really quite reasonable).
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I don't really care about how important realities are dealt with. What I do care about is resource depletion and environmental degradation. I am especially concerned that nobody wishes to put a cost on using the rapidly diminishing commons. We are approaching another tragedy of the commons and problems with automobile emissions and fuel usage are a sizable component. (Geezer, my taxes are really quite reasonable).
I agree Steve (except for the tax bit [:D]) What we really need to do is re-engineer the whole process. A very significant amount of fossil fuel is being spent by people simply going to and from their places of work. We might say that can be solved by the use if public transport, but, actually that's not necessarily true. For example, the real energy costs associated with rail transport are actually a lot higher than some people think (I'll probably need to dig up some data to justify that statement!)
I think figuring out methods to eliminate a lot of commuting entirely ought to be a high priority. That's just one example of course. Now I'll probably get beaten up by Peppercorn for derailing his thread again [;)]
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Lol! - 'derailing', what are you like?!
I would like to see these figures on Rail, but even if they are high right-now I can't think of any good reason why that has to be the case - if it's down to running lots of trains too empty then it;s time to do something about that.
I'm always amazed by how many vehicles are whizzing around during the middle of the day, and not just delivery vans, etc. In short it;s not just work traffic (although this cases the majority of jams [or is it the school run?!]) - people don;t think twice about using the motor vehicle, but I agree that changing peoples behaviour is not just about levying ever higher taxes.
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I'll see what I can did up on the rail thing. I seem to remember it's not just the underutilization of capital equipment, but the actual energy consumed per person mile is really quite high. I was quite surprised when I read it myself. Unfortunately, I've no idea where I saw it now.
It's an interesting example of how it's always a good idea to challenge the conventional wisdom. (You may have noted a certain tendency to do that on my part.)
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Wikipedia had a good article on the costs of public transportation vs cars. Obviously one of the big issues it the typical 1.5 people per car.
http://en.wikipedia.org/wiki/Fuel_efficiency_in_transportation
I think it is heavily US modeled, but down at the bottom there are also some UK links.
http://en.wikipedia.org/wiki/Fuel_efficiency_in_transportation#UK_Public_transport
The problem is that for public transportation to be practical, there has to be access. I.E. A bus should go within 1/4 or 1/2 mile of every place in the city, and should do it from about 5AM to 2AM. Doing so, one ends up with a lot of buses circling the city empty.
The public transportation companies don't seem to like to have a mix of, say typical 15 passenger vans, plus large buses. Run the small vans on off-peak hours, and the big buses during rush hour.
Same thing for commuter trains. They are worthless if you don't have access. So the average ridership is low. Although, this would vary a lot from community to community. In many parts of the world, there aren't other "alternatives", and they also make schedules to try to keep the trains full.
One efficient "commuter" train system that I've been on was the Seattle Tacoma "Sounder"
http://www.soundtransit.org/x71.xml
What is unique about it is that it only has northbound trains in the morning and southbound trains in the evening (it looks like there are a couple more options now for reverse commuting). When I was on it, the train was packed for most of the trip. And it appears as if they've added several more trains in the last couple of years.
I assume they have "train barns" at either end so with the exception of the reverse commutes, most of the trains run one way twice a day, with perhaps one or two trains running 3 ways.
Sorry, I don't have actual ridership and efficiency figures for the Seattle Sounder system. It just seemed packed when I was on one of the trains a couple of years ago, and it appears as if the system has expanded since then.
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Thanks Clifford.
The one that's very significant is the "efficient hybrid" from the US Passenger Transportation in the Wiki page. If these figures are to believed, it's almost twice as energy efficient as commuter rail links in the US.
I do have a personal bias in favor of all forms of rail transport, but I suspect these figures don't even take into account the depressingly low capital utilization of commuter trains and rail infrastructure. Apart from rush hours, most of the stuff is grossly underutilized.
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Apart from rush hours, most of the stuff is grossly underutilized.
Which is why the Seattle-Tacoma trains only run during rush hour, and primarily in one direction.
And, in our "fast-food world", public transportation can often add significant amounts of time to one's commute.
To ride the train from Eugene to Portland... I have a 10 mile bicycle ride to the Eugene train station (other means of local commuting are inconvenient). It then takes 3 hrs on the train rather than 2 hrs of driving. And, once in Portland, I'm about 5 miles from my destination. And since there is no secure place to park a car or bicycle... I end up spending an extra $5 to take the bicycle on the train with me. The 2 hr drive to Portland suddenly becomes a half-day trip if planned well (the last time I ended up sitting in the train station for an extra 2 hrs).
Personally, I find flying so miserable that I would rather drive 8-12 hours than to fly. Bullet trains might help slightly.
I hate the ideas:Everyone pays different prices for the same flight.
You essentially get punished if you don't plan 1 to 3 months in advance.
Exorbitant prices charged for parking.
Airport access is inconvenient at best.
One is often stuck with a rental car at the other end.
In the past, I calculated that it was virtually identical in time to fly 250 miles between St. Louis and Kansas City as it was to drive between the two.
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Apart from rush hours, most of the stuff is grossly underutilized.
Which is why the Seattle-Tacoma trains only run during rush hour, and primarily in one direction.
Er, I think it's the other way around. The Seattle-Tacoma trains and the railway infrastructure are a grossly underutilized capital asset because they only run during rush hour. It's the same problem that all commuter railway systems suffer from. If commuters had much more flexible working hours, it might help to reduce the scale of the problem.
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"The problem is that for public transportation to be practical, there has to be access. I.E. A bus should go within 1/4 or 1/2 mile of every place in the city, and should do it from about 5AM to 2AM. "
No it doesn't.
Public transport IS practical. Just about everywhere has it. Practically none run that sort of schedule.
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"The problem is that for public transportation to be practical, there has to be access. I.E. A bus should go within 1/4 or 1/2 mile of every place in the city, and should do it from about 5AM to 2AM. "
No it doesn't.
Public transport IS practical. Just about everywhere has it. Practically none run that sort of schedule.
It depends on the place...
Fortunately I'm pretty close to a bus line. The nearest bus to my house (in Eugene, OR) is 4 miles one direction, and 5 miles the other direction. First "inbound" bus leaves at 7:10 AM with 4 buses a day. The last outbound bus leaves town at about 6:00 PM. So much for "late nights".
In Portland, Oregon.
The first Red Trimet Max Line leaves downtown at 4:02 AM.
The last Red Trimet train leaves towards downtown at 11:49 PM, and reaches the end of the run at 12:50.
The first connecting bus heading downtown that I could ride leaves around 5:00 AM, and arrives downtown at 5:30.
And the last connecting bus leaves downtown at 12:01 AM.
Since my primary use of public transit in Portland is to connect with planes & trains, it is always a pain to make sure I can catch the public transit connections.
In NYC, the trains run almost around the clock, but that is more like a different planet.
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Darn it [>:(] If you guys want to talk about trains all day, start a new thread!
[;)]
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Sorry.
I think we concluded that there was more hype than reality with the efficiency of public transportation.
Where were we?
I think the EPA testing often reports in PPM.
However, it also appears as if the standards are actually in either gm/HP-hr
or if they are expressed in gm/mile, they also include vehicle classifications.
So, in a sense, all vehicles should be treated equally.
However, it may depend on the actual implementation of the standards.
If the question is why there are different vehicles in Europe and the USA... I doubt it is due to the emission standards. They seem to be close enough that there must be a different explanation. My guess is that it has to do with the extreme redundancy in the testing and approval process. And, while one might think a company would just have to bring new vehicles to the USA, they also have to setup a support network which means a significant investment.
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I've heard that California has had particularly strict emissions standards (for smog reduction) for a number of years, but I don;t know whether they are (now) any stricter than other States, or in fact Europe. They may have over-pushed the pollutant standards (particularly NOx) to the (further) detriment of mechanical efficiency.
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I've heard that California has had particularly strict emissions standards (for smog reduction) for a number of years, but I don;t know whether they are (now) any stricter than other States, or in fact Europe. They may have over-pushed the pollutant standards (particularly NOx) to the (further) detriment of mechanical efficiency.
California pretty much set the pace that everyone else followed. Yes - they were so concerned about smog that they made catalytic converters essential, and they have to be fed a certain amount of fuel to keep them working at the stoichiometric point, so the combined thermal efficiency of the system drops. Initially I think this made quite a difference to fuel consumption, but I suspect that's no longer the case.
Concerning railways, let me just say ... OUCH! [B)]
No need to shove!! I'll have you know I've been thrown out of far better threads than this!
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Concerning railways, let me just say ... OUCH! [B)]
No need to shove!! I'll have you know I've been thrown out of far better threads than this!
Lol! [;D] I must be getting a Napoleon complex!
In reality, I like a good discussion on the Joy of Tracks as much as the next geek! [;)]
Good info on California - I often see that State's name appear on quite alot of articles summarising of pollution control history. Now I know why [:)] Do you honestly think that the days of paying Peter (efficiency) to rob Paul (air-quality) are past (what with modern ECU, valve-timing, etc)?
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Some of the early smog controls were a little counterintuitive, such as adding an air pump (powered by the engine) to pump fresh air into the exhaust manifold.
It probably served a minor purpose of oxidizing some exhaust gases.
In general, emissions control is about burning no more, and no less fuel than you need. It is a good idea, and should have no significant negative impact on the fuel efficiency.
The bigger complaint is that one doesn't necessarily get maximum power output with a "detuned" engine.
The DPF burnoff is different because it specifically sends unburnt fuel into the exhaust system. I don't remember the exact numbers, but the calculations I saw about fuel wasting seemed significant.
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Clifford, what's the DPF burnoff?
There must be quite a bit of energy wasted by the cat. They get really hot! We need to get BC to explain how this stoichiometric thing really works. All I know is that the O2 sensors are critical for maintaining it.
Peppercorn, I'm not confident about my view of the "state-of-the-art", but I don't hear people complaining about the power lost to emission controls the way they did twenty or so years ago. Also, the power per displacement values have gone up considerably, and they are probably exceeding the values that were typical prior to the institution of emission controls.
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Anyway, back at the topic.
Given the engine capacity, the RPM and the air temp and pressure you can convert from ppm to g/km anyway so who cares which one they quote?
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Anyway, back at the topic.
Given the engine capacity, the RPM and the air temp and pressure you can convert from ppm to g/km anyway so who cares which one they quote?
I don't think that was the question BC. By "driving cycle", I think the OP meant something other than constant power output.
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So?
You can still do the calculation. In both cases you would need to sum the result over the course of the driving cycle.
A peak just measures "how bad is this engine at its worst?" which isn't a bad thing to know.
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So?
You can still do the calculation. In both cases you would need to sum the result over the course of the driving cycle.
A peak just measures "how bad is this engine at its worst?" which isn't a bad thing to know.
That is true, but I'm not sure it's what the OP wanted to know.
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Our longer-distance trains in the UK must be well utilised (such as the East Coast Main Line). I've rarely managed to get a seat, whether it's Thursday lunchtime, Friday afternoon, or Sunday afternoon. It's always chock-a-block.
Despite our trains being twice the price of most trains elesewhere in Europe, they're now deliberately increasing prices to "manage" demand...
That said, the late-evening all-stopping trains from Liverpool St (London) to Cambridge often only have half a dozen people in a 4- or 8-carriage train when they approach Cambridge.
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Bored chemist. You said- "Given the engine capacity, the RPM and the air temp and pressure you can convert from ppm to g/km anyway so who cares which one they quote?" Maybe I missed the context, but the difference between ppm and g/km is that a small lightweight vehicle and a heavy overpowered vehicle can have the same ppm emission, but the actual amount of emissions are very different. The amount of emissions is what is important to air quality, and the standards don't even include CO2. Steve
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Our longer-distance trains in the UK
Shhhhhhh. Peppercorn gets all bent out of shape when we mention trains.
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Clifford, what's the DPF burnoff?
In 2007, a "Diesel Particulate Filter" (DPF) was added to most Diesel vehicles in Europe and the USA.
It is like a catalytic converter, but optimized to trap the fine particles in Diesel smoke. Although, there have been concerns that it just takes large particles and makes them smaller... and more invasive.
Apparently it is run somewhat cool, and periodically gets plugged, at which point unburnt fuel is injected into the exhaust stream to increase the temperatures in the DPF and burn off the soot.
Obviously this wastes an amount (not quite sure how much) of Diesel fuel that goes directly into the exhaust stream without generating power.
The early systems apparently reprogrammed the fuel injectors to give a burst of fuel during the exhaust stroke of a 4-stroke engine. This actually ended up causing problems with biodiesel causing oil dilution (slowly rising oil levels... if my car would only do that!!! [::)])
I think the problem with the late injection is central to how a Diesel engine is designed.
In the compression cycle, the engine compresses 100% air. Near TDC, the fuel is injected and burns rapidly.
If unburnt fuel is then added into the cylinder during the exhaust stroke, then some may get past the rings but probably not much (although the biodiesel may stick to the cylinder walls). But, we would have to assume that some of the unburnt fuel remains in the cylinder.
The next stroke would be another compression stroke. If any biodiesel remains in the cylinder, this hits it with high pressure, perhaps creating some blowby.
The biodiesel doesn't evaporate out of the oil like gasoline would with a good crankcase ventilation system, and the oil slowly becomes contaminated with biodiesel at the risk of polymerizing or causing other problems in the lubrication system.
Anyway, many of the manufactures are now doing post-cylinder burnoff cycle injection (still putting unburnt fuel into the exhaust stream, just not in the cylinders).
I believe that 2011 vehicles are now also adding a Urea tank. I forgot exactly what it is supposed to do, but the Urea agents are slowly consumed at a rate of about a gallon or so per fillup of fuel (for a large pickup). And, no, I don't think the manufactures encourage the use of biologic sources of urea. [xx(]
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the standards don't even include CO2. Steve
The standards do include CO2 as the amount of carbon dioxide is directly proportional to the amount of fuel consumed. As fuel standards change, so do the CO2 standards. Anything that doesn't go out the exhaust pipe as carbon dioxide would either being released as unburned hydrocarbons or carbon monoxide.
In Europe, they tax based on the fuel consumption/CO2 emissions with the 99gm/km vehicles having the lowest taxes in the UK.
The EPA tests usually give a fuel efficiency estimate, but I don't believe it is being used as a requirement, and it would be difficult to accurately measure without real-world driving conditions, although I suppose they could rapidly simulate acceleration and various traffic conditions.
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Clifford:
You will have to explain this further because it is my understanding that efficiently burned fuel has CO2 as a main component of exhaust. If CO is present, the fuel hasn't been completely burned and the engine would be less efficient. CO is a main component of wood gas that can be burned in an engine. I didn't think there was any way to burn fossil or bio fuel without creating CO2.
Steve
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Clifford:
You will have to explain this further because it is my understanding that efficiently burned fuel has CO2 as a main component of exhaust. If CO is present, the fuel hasn't been completely burned and the engine would be less efficient. CO is a main component of wood gas that can be burned in an engine. I didn't think there was any way to burn fossil or bio fuel without creating CO2.
Steve
Steve,
I believe you are quite correct. The mass of CO2 is largely proportional to the mass of fuel consumed, but, with spark ignition gasoline engines at least, there is some CO left in the exhaust, presumably because the combustion process is not perfect. If I remember correctly, the CO is burned off in the catalytic converter and does no work.
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That is what I said...
Gasoline is a mixture of different hydrocarbons, but for simplicity:
Say you were burning Octane... C8H18.
With perfect combustion, you would get:
C8H18 + (12.5)O2 --> 8CO2 + 9H2O
So, it wouldn't make any difference whether you counted the Octane (C8H18) that you put in, or the Carbon Dioxide (CO2) that was released. The numbers would be directly proportional in an 1:8 MOLAR ratio.
Different units may be convenient with the measurements, but it is still proportional.
If your engine wasn't running very well, and you had a rich mixture (too much gas, not enough air)... and you cut off the CAT... then you might get (for example):
C8H18 + (10)O2 --> 6CO2 + 7H2O + CO + CH4
In the second case, you are only getting a 1:6 Molar ratio of Octane to Carbon Dioxide, but only because you are getting other pollutants coming out the tailpipe. And, like you said, you probably would have a loss of power.
Interestingly enough,
Even though you began with a liquid (at Room Temp), and ended up with a gas (at Room Temp), you will be getting more weight in Carbon Dioxide than you originally had with Octane.
Molecular Weights:
H: 1
C: 12
O: 16
Octane: C8H18
12*8 + 18*1 = 114 grams/mole
CO2
12*1 + 16*2 = 44 grams/mole
But at the 1:8 ratio, you get:
114*1 grams Octane (per mole) --> 44*8 grams CO2 (per 8 moles product)
114 grams Octane --> 352 grams CO2
(note, I got the words "rich and lean" backwards... fixed)
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Woooohoo! Excellent Clifford.
That's the sort of detail that "chemically challenged" twits like me are lacking.
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Wow! I take my eye off this thread for a few days and it explodes! (Must be all that unburnt fuel hanging around [:D]) ... Not that I'm complaining - Most interesting stuff. Thanks all!
Bored chemist. You said- "Given the engine capacity, the RPM and the air temp and pressure you can convert from ppm to g/km anyway so who cares which one they quote?" Maybe I missed the context, but the difference between ppm and g/km is that a small lightweight vehicle and a heavy overpowered vehicle can have the same ppm emission, but the actual amount of emissions are very different. The amount of emissions is what is important to air quality, and the standards don't even include CO2. Steve
I agree and that was what I was hoping to discuss.
I do think that by now we've established that Standards across the world do limit by (or at least include) g/km (or equiv.) which should discourage the dirtiest vehicles, but does need them to have more and more 'involved' cats.
I'd be keen to see a standard that says only 'x' percent of pollutants can be stopped post-combustion - done over a standard driving cycle. In other words, can we move away from this 'run for performance, clean-up later (post-combustion)' mentality?
...
Additionally, with the mention of all this chemistry above, I'd like to know people's perception of what good-ol' Nitrogen means when we assess efficiency? I mean if we ignore NOx as a pollutant, doesn't it in some instances actually represent an increase in mechanical efficiency when it reacts with air (at post 1200degC I believe) - ie. more expansion via a endothermic reaction.
BTW, I'm not saying we should be encouraging it's formation.
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Clifford:
I am not responsible for my response to you because, apparently, my head was out to lunch yesterday and I don't have any idea what it was doing. I am concerned about any credit card bills that might unexpectedly show up.
Steve
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As far as Pre-CAT engine performance.
Here is an interesting article about retrofitting a Catalytic Converter into an older car that wasn't ever designed for it.
https://webshop.fiat500126.com/index.php/sites/view/57-1-exklusiv_g-kat.html
As this regulating process is so important, uncontrolled catalytic converters can only clean about 45% of the exhaust fumes, whereas computer controlled catalytic converter systems can clean 90-95%.
Anyway, so one can't just slap a Cat onto an older engine without more work. And, the engine tuning (and a dynamic oxygen/fuel mix) are vital.
My first car with a Catalytic Converter, an '84 Renault Encore, was probably running a little rich near the end of its days. I failed a smog test.. yanked the Catalytic Converter... There was absolutely nothing inside... Just a bare pipe. & no, it wasn't reamed. Either it was a faulty component from manufacture (unlikely). My interpretation is that I was burning oil or something... and it caused the CAT to run very very hot... which caused it to destroy itself.
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Odd!
The catalyst is supported on a substrate that is basically a rock. It would cheerfully sit there glowing red hot.
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Maybe it had a cataclysmic episode?
Or maybe somebody requisitioned it
http://www.edmunds.com/auto-insurance/in-under-two-minutes-catalytic-converter-theft.html?articleid=132109&
although I have to admit it was pretty clever of them to substitute a dummy so you wouldn't notice, so that seems a bit unlikely.
Are you sure it even had a cat? The thing you were looking at might have been some sort of fiendish French pre-muffler tuning thingy to smooth the gas flow after the manifold.
EDIT: It looks like an 84 Encore should have a cat, so it is strange. Perhaps the ceramic substrate shattered (I think they are fairly fragile) and the pieces ended up in the muffler.
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As far as the Renault...
That was a few years ago.
It was an 1984.
Should have had a CAT. They would have been required from about 1976 or shortly thereafter.
My parents bought the car new.
I got it with a bit over 100K miles.
I did the first SMOG test ever after moving to Portland around 1998, with close to 200K miles. The old CAT may still be sitting in Scrap metal somewhere... if so, I'll try to get some photos, but there was nothing inside (not even a hole blown through).
In the first 200K miles, it blew the original muffler, and had 3 replacements. 2 done by a "shop", and one by myself. Neither myself or my father would have intentionally had the CAT disabled.
The theory of "cat guts" in the muffler might explain the burnt mufflers.
I haven't seen any other worn out CATS, so I don't know what I should have expected.
The actual repair, in the late 90's was a pain to do, but less than $100 for the replacement CAT. With the replacement CAT, it barely passed SMOG testing, but that was all I needed.
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Nitrogen and NOx.
I left it out of the earlier equations (Page 2) because it is not really from fuel.
Air is about:
78% Nitrogen (N2)
21% Oxygen (O2)
0.93% Argon (Ar)
0.04% Carbon Dioxide (CO2)
So, in the engine, you have a mix of Gasoline or Diesel (hydrocarbons), Nitrogen, and Oxygen.
Your Gasoline does not contain significant amounts of Nitrogen, that comes from the air.
The reason it is called NOx is that it is a mixture of various Nitrogen Oxides (NO, N2O, NO2, N2O3, N2O4, N2O5, (HNO3 & NO3-)).
So...
N2 + O2 --> NOx (unbalanced)
It is supposed to be a slightly endothermic reaction (requiring energy), which is why there are only small amounts of it in the atmosphere. And it will break down to N2 & O2.
I believe that it is related to high combustion temperatures, advanced timing, and excess Oxygen.
There are notes that N2O will catalyze the formation of Ozone in the stratosphere. And, unlike low level O3 that apparently does not get up to the stratosphere, low level N2O may actually get up to the stratosphere to produce more Ozone.
Unfortunately, while NOx may be a benefit in the Stratosphere, it does cause respiratory problems down here on earth.
Notes also indicate that it may be related to the formation of the NO3- radical and HNO3 Nitric Acid. And thus Acid Rain. Actually, I see notes that Aqueous Nitric Acid (HNO3) will decompose into Nitrogen Dioxide (NO2) and Oxygen (O2).
Anyway, it might not be bad to minimize the environment that makes the Nitrogen Oxides.
Note, you have a fine balance on tuning, especially with the NOx.
Hotter Temps, More Oxygen, Advanced Timing --> better combustion, less hydrocarbons, less Carbon Monoxide.
Hotter Temps, More Oxygen, Advanced Timing --> Increased NOx.
So, what gives a "clean running car" for other pollutants, can be problematic with NOx, and visa-versa.
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Diesel vs Gasoline.
Diesel engines are the primary producers of Particulate Matter (PM). Black smoke from a gasoline engine indicates problems.
Diesel engines also produce higher NOx because of increased cylinder pressures, and leaner fuel/air mixtures.
Diesel engines consume less fuel, even when taking into account energy density, and thus also produce less CO2.
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Note, you have a fine balance on tuning, especially with the NOx.
Hotter Temps, More Oxygen, Advanced Timing --> better combustion, less hydrocarbons, less Carbon Monoxide.
Hotter Temps, More Oxygen, Advanced Timing --> Increased NOx.
So, what gives a "clean running car" for other pollutants, can be problematic with NOx, and visa-versa.
So, is more mechanical work made available from N2's reacting with O2's (absorbing some of the heat - endothermic) to make NOx's ? Through the resultant Oxides of Nitrogen taking up more room than in elemental form.
Hence:
I mean if we ignore NOx as a pollutant, doesn't it in some instances actually represent an increase in mechanical efficiency when it reacts with air (at post 1200degC I believe) - ie. more expansion via a endothermic reaction.
Also I was under the impression that having ignition timing set too advanced would be fighting the engines momentum, so to state this is more efficient is ambiguous.
As a counter-example:
An ideally set up genset engine (One with a very flat low torque curve - ie. All HP) would have an ignition leading to just the start of positive cylinder pressure at TDC. That is, as much of the expansion work is available to push the piston down. Of course, a compromise is made so that ideally all the expansion has occurred by the time the piston reaches the bottom of the stroke (this is where a true Atkinson cycle has an advantage).
Lean-burn is the situation where most concern has been focused about NOx formation - Here NOx is mainly brought about by the greatly reduced effect of charge cooling from fuel evaporation (less fuel to air mass). The slower flame speed in lean-burn mode can also cause burnt valves and valve-seats and this also feeds-back to create a peak temperature region in the cylinder head near the valve, which can cause additional NOx formation.
I have rambled a bit, but what I really want answered (slightly off-topic though it is, Tut-tut!): I still don't know for sure whether an engine producing high NOx counts has a better mechanical efficiency than one with next to none - ?
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I still don't know for sure whether an engine producing high NOx counts has a better mechanical efficiency than one with next to none - ?
As an Anecdotal Physicist, I would have to say yes on the grounds that cats were pushed heavily by California to reduce smog. As soon as they were introduced, everbody started complaining that their cars had no guts at all.
Further anecdotal evidence: The 1.6L Fiat 126 I had in the UK in 1982 would blow the doors off just about any smog equipped vehicle of similar vintage I ever drove in the US, some of which had far larger engines.
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Clifford,
I bet your Encore was a real "babe magnet" [:D]
A friend of mine bought a Chevrolet Chevette when he came to the US. The guys at work used to harass him with comments like -
"Oooo please Alistair. Can we go to lunch in your 'vette?"
(In case anyone doesn't know, in the US, 'vette is a common abbreviation for a Corvette, which has slightly better performance than a Chevette.)
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Clifford,
I bet your Encore was a real "babe magnet" [:D]
It was better than the "Pumpkinmobile" which it replaced... otherwise known as a 76 AMC Hornet "Sportabout"... nothing sporty about it though!!! Oxidized Pumpkin Orange!!! Why a stationwagon was called a "Sportabout" is beyond me.
As a real "rebel"... I tried the pedal to the medal on the Utah freeway with the AMC... I think I got up to about 75 MPH after a few minutes.
I believe the 76 AMC was the last non-catalytic model. It was supposed to take unleaded gasoline, but no CAT. The dealer told Dad how to cut out the little ring in the filler spout to allow any fuel nozzle (during a time before all stations carried Unleaded, and there was a significant price differential). It had other things like the air pump in the exhaust manifold... that either oxidized some Carbon Monoxide, or diluted it, nobody was quite sure.
Which is a good point with the "PPM" measurement..... how does the early air pump affect it?
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A friend of mine bought a Chevrolet Chevette when he came to the US.
D'ya mind! I learnt to drive in a 'vette! To be fair this was a Vauxhall Chevette and I was 16, so not that official!
On the other hand my brother was 13 and had to sit on an old chair cushion to see over the steering wheel [:D]
Luckily there was a handy bit of waste ground the other side of the railway where we lived to, erm, practice on [:P]
'Toto, I've a feeling we're not in Kansas any more' - That's how off topic it's becoming [:D]
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Note, you have a fine balance on tuning, especially with the NOx. ...
So, is more mechanical work made available from N2's reacting with O2's to make NOx's ? .... blah blah blah
I don't think making the NOx actually improves the performance.
For Nitric oxide (NO), you start with dimers and end with a dimer, so you end up with no net change in moles.
N2 + O2 --> 2NO
But, if instead you are making Nitrogen Dioxide (NO2), then you end up with fewer moles.
N2 + 2O2 --> 2NO2 (3 moles --> 2 moles).
And, thus the formation of NOx would actually reduce the energy.
Assuming it is mildly endothermic, that means lower temperatures, and less energy too.
Breaking down the NOx, would produce more moles of product, and more kinetic energy.
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For Nitric oxide (NO), you start with dimers and end with a dimer, so you end up with no net change in moles.
N2 + O2 --> 2NO
But, if instead you are making Nitrogen Dioxide (NO2), then you end up with fewer moles.
N2 + 2O2 --> 2NO2 (3 moles --> 2 moles).
And, thus the formation of NOx would actually reduce the energy.
Assuming it is mildly endothermic, that means lower temperatures, and less energy too.
Breaking down the NOx, would produce more moles of product, and more kinetic energy.
I'm sure your analysis is correct but is it purely a matter of counting moles for working out if there is an increase in volume? (I mean for a steady temperature that this is almost certainly not).
Can you also explain why, as mentioned earlier, advanced timing (in relation to a 'traditional' advance) will give a better, more complete burn?
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Uhhh....
It has been too many years since I've studied "Science" [xx(]
But, from the Ideal Gas Law:
pV = nRT
pressure * volume = moles * Constant * Temperature
R = 8.314472 J/K·mol
So...
I think the pressure is independent of WHAT it is, but only dependent on how much you have (in moles) and what the temperature is.
So, anything that would reduce the temperature (endothermic reaction) or would reduce the moles, would also reduce the pressure.
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I'm not an expert on things like Engine Timing.
I need to get one of those exhaust gas gizmos for playing with ;)
I think advancing the timing increases the time for combustion... and thus I would expect a more complete burn.
But, perhaps there are other influences.
I'm sure there is more technical info on the web somewhere.
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I think advancing the timing increases the time for combustion... and thus I would expect a more complete burn.
I believe that's it. The ignition timing is not fixed for that reason. It varies with engine speed. In ye olden days we had mechanical distributors that had a centripetal advance mechanism. Presumably these have been superceded by fiendishly complicated electronics (and firmware even!) to discourage people like me from doing my own repairs.
I changed the spark plugs on my car recently, and I was slightly surprised to discover that the entire operation took well over two hours! The actual removal and replacement of the plugs only took about fifteen minutes. The rest of the time was spent disassembling and reassembling a load of kit that looked like it belonged more properly in a CRT type TV set [:D]
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I think advancing the timing increases the time for combustion... and thus I would expect a more complete burn.
Maybe I was unclear in my inquiry. Perhaps if I were to ask why you think that, in traditionally set-up engine, having the timing set for a burn that ends later than the ideal - will reduce NOx formation.
Or is it more to do with purposely leaving some CO/HC to oxidize at the Cat and drive the thermal dissociation of NOx's?
In ye olden days we had mechanical distributors that had a centripetal advance mechanism. Presumably these have been superceded by fiendishly complicated electronics
Those old points systems do wonder pretty horribly around the timing though. Anyone who's ever used a timing-light on an old car, esp. with a few decades ware in the dissy will have seen this. As I'm sure you know really, electronic ignition has much to be said for it.
The rest of the time was spent disassembling and reassembling a load of kit that looked like it belonged more properly in a CRT type TV set
I'm sure there is an element of keeping the buyer from fixing their motor too easily (or at all!), but having coil-packs, etc is a really neat advance in autos IMO.
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Remember that NOx is a combustion byproduct that is essentially opposite from Carbon Monoxide (CO), Hydrocarbons (HC), and Particulate Matter (PM).
Think of NOx as too much oxygen, and too much combustion.
CO, HC, PM, are essentially too little Oxygen, and too little combustion.
Thus graphs of NOx often go opposite the others.
A quick web search indicates suggestions of advanced timing increases NOx, and retarded timing decreases it.
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A little aside,
NOx can also be used as an oxidizer.
So, if you took: Dinitrogen tetroxide, (N2O4)
N2O4 --> N2 + 2O2 (1 mole --> 3 moles). Also, one gets a higher oxygen/nitrogen mix than one would normally have in air. Being Exothermic, it would also increase the combustion temperatures (and also increase cylinder pressures).
So, while producing NOx in the engine and releasing it into the exhaust takes away power. Adding excess NOx to the intake increases power (and likely also causes a significant amount to be released in the exhaust). But, if your goal is maximum acceleration, adding some NOx into your intake might just give you the edge you need.
(all based on the Ideal Gas Law which should more or less apply).
pV = nRT
(Note for the "topic police". Sorry if we are rambling a bit. But a rough understanding of emissions is critical to any discussion of decreasing them, or otherwise managing the emissions.)
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Remember that NOx is a combustion byproduct that is essentially opposite from Carbon Monoxide (CO), Hydrocarbons (HC), and Particulate Matter (PM).
Think of NOx as too much oxygen, and too much combustion.
CO, HC, PM, are essentially too little Oxygen, and too little combustion.
Thus graphs of NOx often go opposite the others.
But too much oxygen is also a prerequisite of 'lean-burn'. Unfortunately localised high temperatures can be difficult to avoid with lower fuel vaporisation cooling of lean-burn and may lead to NOx formation.
A quick web search indicates suggestions of advanced timing increases NOx, and retarded timing decreases it.
I suggested the reason for this: 'Is it more to do with purposely leaving some CO/HC to oxidise at the Cat and drive the thermal dissociation of NOx's?'
So it is an indirect effect....