Smog test and octane
02-06-2009, 11:50 AM
#11
AudiWorld Senior Member
there are several paths to, and at least two different "octane rating" systems...
<center><img src="http://www.sunoco.ca/data/1/rec_imgs/114_PS_CR_1.gif"></center><p>Octane, t-e lead, and ethanol (amongst others) can all be used to that end. Obviously the use of these different chemicals, varies widely. See "Regional Variations" in article below.
Ethanol's RON is (129 (MON 102, AKI 116)), high enough that it is used to raise gasoline's octane <i>rating</i>.
Re: above illustration: "Up to 10% ethanol enhanced since 1996! I believe that that limit is only there, to protect some plastic components in some fuel systems in some old cars. See your owner's manual, this may also be Audi's reco'd limit.
We want a deftly controlled ignition by spark alone, not by compression, nor glowing deposit, because we want max. compression, because that gives the best power and economy. The highest OEM reco'd fuel is going to allow the ECM to give us that. This is because that <i>proper</i> fuel allows max. design ignition advance, <i>soonest</i>.
Running today's high-test where it is not required is wasteful, yes, but not because the high-test is slow-burning and therefore dirtier. It is because to get the same power delivered, you have to put your foot down farther, and that extra consumption trumps the lower cost of regular.
from: wikipedia.org:
"higher octane fuels have higher activation energies, it is less likely that a given compression will cause detonation.
It might seem odd that fuels with higher octane ratings are used in more powerful engines, since such fuels 'explode' less easily. However, an explosion is not desired in an internal combustion engine. An explosion will cause the pressure in the cylinder to rise far beyond the cylinder's design limits, before the force of the expanding gases can be absorbed by the piston traveling downward. This actually reduces power output, because much of the energy of combustion is absorbed as strain and heat in parts of the engine, rather than being converted to torque at the crankshaft.
A fuel with a higher octane rating can be run at a higher compression ratio without detonating. Compression is directly related to power"
As to emmisions, your 3-way cat has to work less, will last longer, and works best at delivering the cleanest power at stoichiometric, which is what your ECM is trying to give you, and what your O2 sensor is dithering about. Now-a-days, that system authority given to the O2 sensor in closed loop, its performance is what gives you the lowest and least harmful combo of unburnt HC, CO and the NoX's.
A really clean pass of an E-test requires those components to be working properly. A high HC result <i>also</i> means your throwing extra money <i>out</i> the tail-pipe unnecessarily.
Using a higher octane than specified for peak performance means your throwing extra money <i>in</i> the tank needlessly. If it where also dirtier for that reason alone, I'm sure you wouldn't be allowed to do it.
Notwithstanding the following:
"When the throttle is partially open, only a small fraction of the total available power is produced because the manifold is operating at pressures far below atmospheric. In this case, the octane requirement is far lower than when the throttle is opened fully and the manifold pressure increases to atmospheric pressure"
...the use of the highest OEM reco'd fuel for peak performance is probably going to <i>also</i>; give you peak mileage.
If your Audi 90 produces higher HC on todays higher octane rated fuel, (and frankly I do not yet understand why it would) I would think it requires, other attention.
There is no significant short-cut to a clean tail-pipe that would not also be good, every other day.
It just doesn't make sense that on one hand you want the engine fully warmed-up prior to the E-test, yet also say: put in a lesser (or a greater) than the recommended fuel.
I think that today's max. 10% ethanol blend fuels can't help but be cleaner than non E-blends. Ethanol is drinkable; gas or lead, not so much.
<img src="http://www.jagweb.com/aj6eng/af_effects.jpg">
Look (above) at the extremely narrow band within which the HC, CO, & NOx emmissions are minimized in. Note also how this corresponds to the best spots on the torque and fuel consumption curves. That alone, ought to be reason enough to get you motivated to want to be able to run clean every day. Regular or Premiium, regardless; if your car can't deliver those above conditions, it shouldn't pass!
IMHO, our ability to continue hot-rodding is probably quite contingent on how clean a fashion we can do it. Please note all the (currently voluntary) government programs whereby they will pay you to crush your >10 yr. old car and subsidize your buying of a new one.
From my cold dead hands.
Ethanol's RON is (129 (MON 102, AKI 116)), high enough that it is used to raise gasoline's octane <i>rating</i>.
Re: above illustration: "Up to 10% ethanol enhanced since 1996! I believe that that limit is only there, to protect some plastic components in some fuel systems in some old cars. See your owner's manual, this may also be Audi's reco'd limit.
We want a deftly controlled ignition by spark alone, not by compression, nor glowing deposit, because we want max. compression, because that gives the best power and economy. The highest OEM reco'd fuel is going to allow the ECM to give us that. This is because that <i>proper</i> fuel allows max. design ignition advance, <i>soonest</i>.
Running today's high-test where it is not required is wasteful, yes, but not because the high-test is slow-burning and therefore dirtier. It is because to get the same power delivered, you have to put your foot down farther, and that extra consumption trumps the lower cost of regular.
from: wikipedia.org:
"higher octane fuels have higher activation energies, it is less likely that a given compression will cause detonation.
It might seem odd that fuels with higher octane ratings are used in more powerful engines, since such fuels 'explode' less easily. However, an explosion is not desired in an internal combustion engine. An explosion will cause the pressure in the cylinder to rise far beyond the cylinder's design limits, before the force of the expanding gases can be absorbed by the piston traveling downward. This actually reduces power output, because much of the energy of combustion is absorbed as strain and heat in parts of the engine, rather than being converted to torque at the crankshaft.
A fuel with a higher octane rating can be run at a higher compression ratio without detonating. Compression is directly related to power"
As to emmisions, your 3-way cat has to work less, will last longer, and works best at delivering the cleanest power at stoichiometric, which is what your ECM is trying to give you, and what your O2 sensor is dithering about. Now-a-days, that system authority given to the O2 sensor in closed loop, its performance is what gives you the lowest and least harmful combo of unburnt HC, CO and the NoX's.
A really clean pass of an E-test requires those components to be working properly. A high HC result <i>also</i> means your throwing extra money <i>out</i> the tail-pipe unnecessarily.
Using a higher octane than specified for peak performance means your throwing extra money <i>in</i> the tank needlessly. If it where also dirtier for that reason alone, I'm sure you wouldn't be allowed to do it.
Notwithstanding the following:
"When the throttle is partially open, only a small fraction of the total available power is produced because the manifold is operating at pressures far below atmospheric. In this case, the octane requirement is far lower than when the throttle is opened fully and the manifold pressure increases to atmospheric pressure"
...the use of the highest OEM reco'd fuel for peak performance is probably going to <i>also</i>; give you peak mileage.
If your Audi 90 produces higher HC on todays higher octane rated fuel, (and frankly I do not yet understand why it would) I would think it requires, other attention.
There is no significant short-cut to a clean tail-pipe that would not also be good, every other day.
It just doesn't make sense that on one hand you want the engine fully warmed-up prior to the E-test, yet also say: put in a lesser (or a greater) than the recommended fuel.
I think that today's max. 10% ethanol blend fuels can't help but be cleaner than non E-blends. Ethanol is drinkable; gas or lead, not so much.
<img src="http://www.jagweb.com/aj6eng/af_effects.jpg">
Look (above) at the extremely narrow band within which the HC, CO, & NOx emmissions are minimized in. Note also how this corresponds to the best spots on the torque and fuel consumption curves. That alone, ought to be reason enough to get you motivated to want to be able to run clean every day. Regular or Premiium, regardless; if your car can't deliver those above conditions, it shouldn't pass!
IMHO, our ability to continue hot-rodding is probably quite contingent on how clean a fashion we can do it. Please note all the (currently voluntary) government programs whereby they will pay you to crush your >10 yr. old car and subsidize your buying of a new one.
From my cold dead hands.
02-06-2009, 12:24 PM
#12
Incredibly good write-up! Today I can pretty much tell by a visual...
<center><img src="http://pictureposter.audiworld.com/711/properaf.jpg"></center><p>
exhaust tips inspection how my A/F ratios are and to a lesser, albeit closer-than-before determination of emissions related crappola I'm putting out into the environment. Lean and clean does NOT in and of itself represent imminent threat, danger or even less power. Done correctly it simply wipes the floor power-wise with any/all black, sooty, puffy tailpipe deposits on an otherwise identical car. Don't believe it? Take a walk around the pits of ANY ALMS or SCCA national event and look closely at the exhaust tips of those cars in the pits. Yes, you can have your cake (more power) and eat it too (cleaner emissions). They don't "have" to be mutually exclusive!
Basically long as my exhaust tips look like the above pic when day-to-day commuting as well as after running a full day on the road course I'm happy. And getting those tips to look like that in ALL driving conditions I participate in may be the most expensive, challenging, complex and difficult thing I've EVER attempted with an Audi! Let alone an Audi with 104k miles on it!
exhaust tips inspection how my A/F ratios are and to a lesser, albeit closer-than-before determination of emissions related crappola I'm putting out into the environment. Lean and clean does NOT in and of itself represent imminent threat, danger or even less power. Done correctly it simply wipes the floor power-wise with any/all black, sooty, puffy tailpipe deposits on an otherwise identical car. Don't believe it? Take a walk around the pits of ANY ALMS or SCCA national event and look closely at the exhaust tips of those cars in the pits. Yes, you can have your cake (more power) and eat it too (cleaner emissions). They don't "have" to be mutually exclusive!
Basically long as my exhaust tips look like the above pic when day-to-day commuting as well as after running a full day on the road course I'm happy. And getting those tips to look like that in ALL driving conditions I participate in may be the most expensive, challenging, complex and difficult thing I've EVER attempted with an Audi! Let alone an Audi with 104k miles on it!
02-06-2009, 01:23 PM
#13
AudiWorld Senior Member
Thanks. What's up-stream of your tailpipe in particular, & that the resulting colour...
is possible, is one of the most interesting things I've learned here. Previously I just wanted to pass the damn test. Now I know exactly why I want the tester fellow to think his machine may not be working correctly, and that my car couldn't possibly be that clean.
IMHO on any given day lately, gas has historically never been so cheap, and what we are free to technically do with these old cars never more full of possibilities, yet for politics etc., that might not always be the case. We lucky few.
IMHO on any given day lately, gas has historically never been so cheap, and what we are free to technically do with these old cars never more full of possibilities, yet for politics etc., that might not always be the case. We lucky few.
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