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Author Topic: Should limits on vehicle pollutants be averaged thru driving cycle, not max PPM?  (Read 20130 times)

Offline CliffordK

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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.
« Last Edit: 08/12/2010 03:23:22 by CliffordK »
 

Offline Geezer

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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.
 

Offline Bored chemist

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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.
 

Offline CliffordK

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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.
 

Offline peppercorn

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Darn it  >:(  If you guys want to talk about trains all day, start a new thread!

 ;)
 

Offline CliffordK

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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.
 

Offline peppercorn

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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.
 

Offline Geezer

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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!
 

Offline peppercorn

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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)?
 

Offline CliffordK

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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. 
 

Offline Geezer

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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.
 

Offline Bored chemist

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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?
 

Offline Geezer

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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.
 

Offline Bored chemist

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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.
 

Offline Geezer

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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.
 

Offline techmind

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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.
« Last Edit: 10/12/2010 00:07:57 by techmind »
 

SteveFish

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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
 

Offline Geezer

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Our longer-distance trains in the UK


Shhhhhhh. Peppercorn gets all bent out of shape when we mention trains.
 

Offline CliffordK

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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(]
 

Offline CliffordK

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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.

 

SteveFish

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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
 

Offline Geezer

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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.
 

Offline CliffordK

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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)
« Last Edit: 10/12/2010 23:21:03 by CliffordK »
 

Offline Geezer

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Woooohoo! Excellent Clifford.

That's the sort of detail that "chemically challenged" twits like me are lacking.
 

Offline peppercorn

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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.
« Last Edit: 10/12/2010 13:13:56 by peppercorn »
 

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