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Old 04-24-2015, 11:27 PM   #61 (permalink)
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Old 04-25-2015, 08:23 AM   #62 (permalink)
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Quote:
Originally Posted by Cycle View Post
Quote:
Originally Posted by IamIan
BTU/Mile already does .. it includes both the amount of fuel and the fuel's energy density ... thus making it superior to the less information from just using gallons , liters, etc.
How so? What volume of fuel that comprises a single BTU will drive the car for a specific distance?
Explaining:
The specific volume (or weight) of fuel to get 1 BTU will vary with the energy density of the specific fuel.

Propane has a different energy density than gasoline .. different than Diesel .. different than hydrogen .. etc... But 1 BTU = 1 BTU.

The volume of the fuel will change with different conditions (temperature, pressure, etc) ... but the BTU contained in it does not change .. 1 BTU = 1 BTU.

Energy (BTU) is the capacity to do work (volume is not) ... if you want to know the capacity to do work .. you want to know the amount of energy (BTU).

Quote:
Originally Posted by Cycle View Post
Especially considering that different engines will have different efficiencies, some throwing away more of those BTUs than other engines.
Exactly.
What % of that previously sited 5% was due to engine differences alone (ie the portion that did not come from the propane itself.)

Quote:
Originally Posted by Cycle View Post
If we bought fuel by the BTU, his point would have more merit... but we buy our fuel by volume.
Energy is the capacity to do work (ie move the car) .. thus units of energy (BTU) is the best units to use to determine one's ability to do work (ie more the car).

Someone could sell it to me by the BTU .. by the kg .. by the barrel .. for chickens .. for milk .. etc .. etc.

How someone chooses to sell it to me does not effect it's capacity to do work .. thus back to the units of energy (BTU)

Quote:
Originally Posted by Cycle View Post
So it all comes back to volume... MPG.
Disagree .. see above.
Weather you personally like the BTU/mile method or not .. that is the method that was sited to you in the comments made above.

Quote:
Originally Posted by Cycle View Post
As for "it's too small a difference"...
No... It seems you misunderstood.

I'll try again.
How do you differentiate the efficiency BTU/mile effects of:

#1> The Fuel
from
#2> The modifications you made to the engine itself.
and
#3> What is the expected variation (noise) one's result must surpass to indicate a significant signal ?

For example of 1+2:
I can run my ICE with gasoline from gas station A .. get say 50MPG .. Than I modify my ICE to run in Lean Burn .. I buy gasoline from station B .. say I got 60MPG ... the fuel alone is not the only reason for the change in MPG .. The changes made to the ICE itself contribute.

Example of 3:
Same as previous example .. but say I made no modifications to the ICE at all .. is that same 20% variation in MPG from one trip to the next a large enough difference to surpass the 'noise' one would expect from different trips .. and be able to reasonable assume the difference was caused by different gasoline from Station A vs Station B.

Quote:
Originally Posted by Cycle View Post
what about "the amount of fuel per unit volume of air for propane is approximately twice that of gasoline just to reach that fuel's flammability range" and "propane has only ~73% of the energy content of gasoline on a per volume basis" yet "propane still exhibits a higher fuel efficiency than gasoline" don't you understand?
As explained previously .. on an energy basis (BTU/mile) .. the difference is soo small it can easily almost entirely be just from the modifications made to the ICE that produced it.
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Old 04-25-2015, 12:12 PM   #63 (permalink)
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Quote:
Originally Posted by IamIan View Post
Explaining:
The specific volume (or weight) of fuel to get 1 BTU will vary with the energy density of the specific fuel.

Propane has a different energy density than gasoline .. different than Diesel .. different than hydrogen .. etc... But 1 BTU = 1 BTU.

The volume of the fuel will change with different conditions (temperature, pressure, etc) ... but the BTU contained in it does not change .. 1 BTU = 1 BTU.

Energy (BTU) is the capacity to do work (volume is not) ... if you want to know the capacity to do work .. you want to know the amount of energy (BTU).



Exactly.
What % of that previously sited 5% was due to engine differences alone (ie the portion that did not come from the propane itself.)



Energy is the capacity to do work (ie move the car) .. thus units of energy (BTU) is the best units to use to determine one's ability to do work (ie more the car).

Someone could sell it to me by the BTU .. by the kg .. by the barrel .. for chickens .. for milk .. etc .. etc.

How someone chooses to sell it to me does not effect it's capacity to do work .. thus back to the units of energy (BTU)


Disagree .. see above.
Weather you personally like the BTU/mile method or not .. that is the method that was sited to you in the comments made above.


No... It seems you misunderstood.

I'll try again.
How do you differentiate the efficiency BTU/mile effects of:

#1> The Fuel
from
#2> The modifications you made to the engine itself.
and
#3> What is the expected variation (noise) one's result must surpass to indicate a significant signal ?

For example of 1+2:
I can run my ICE with gasoline from gas station A .. get say 50MPG .. Than I modify my ICE to run in Lean Burn .. I buy gasoline from station B .. say I got 60MPG ... the fuel alone is not the only reason for the change in MPG .. The changes made to the ICE itself contribute.

Example of 3:
Same as previous example .. but say I made no modifications to the ICE at all .. is that same 20% variation in MPG from one trip to the next a large enough difference to surpass the 'noise' one would expect from different trips .. and be able to reasonable assume the difference was caused by different gasoline from Station A vs Station B.



As explained previously .. on an energy basis (BTU/mile) .. the difference is soo small it can easily almost entirely be just from the modifications made to the ICE that produced it.
Let's break it down a bit more for you...

The fuel injector is triggered, squirting a bit of fuel.

In a gasoline engine, it squirts 1.4285% of the volume of the air to reach stoichiometric.

In a propane engine, it squirts 2.94 times as much to reach the level where maximum heat is produced (4.2% of fuel in air by volume).

In a propane engine, it squirts 1.68 times as much just to reach the lower flammability limit of propane (2.5% of fuel in air by volume).

That's not a small difference.

Now factor in that propane only has ~73% of the energy content of gasoline.

No amount of compression increase or timing advance will account for that much of a variation in the amount of fuel used on a per cycle basis.
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Old 04-25-2015, 04:38 PM   #64 (permalink)
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Quote:
Originally Posted by Cycle View Post
That's not a small difference.
You're incorrectly applying a response to the 'small difference' reference.

The 'small difference' that has been pointed out to you is not about volume .. nor is it about weight ... re-read above examples such as my 1, 2, 3 above in post #62.

Maybe you'll have better luck if you try and picture this concept with the normal MPG fluctuations seen from driving the same car with no modifications to the type of fuel or the vehicle itself ... the same type of 'small difference' that has been pointed out to you comes up there as well .. What is the standard deviation and how many σ you have of certainty of the significance the results are caused by A and not B ? ... ie ... How large does the difference (in BTU/mile) have to be to have a reasonable degree of certainty that the results are caused by the changes in the fuel and not the changes in the ICE itself ?

Quote:
Originally Posted by Cycle View Post
No amount of compression increase or timing advance will account for that much of a variation in the amount of fuel used on a per cycle basis.
You are incorrectly applying a response about the changes to an ICE.

The previous ICE changes comments described to you are not about fuel volume, nor fuel weight ... BTU/mile ... re-read previous explanation such as my 1, 2, 3 above in post #62 ... or my additional attempt above in this post.
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Old 04-25-2015, 10:41 PM   #65 (permalink)
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Interesting... chemically, stoichiometric for propane is 5:1 air:fuel, but all the sites I've visited said propane's stoichiometric ratio is 15.5:1.

And 100 - ((14.7 / 15.5) * 100) = 5.1613%

So that observed 5% difference in BTU/mile fuel efficiency may just be because propane burns leaner than gasoline. But that's only 1.3548% fuel to air by volume, well below the flammability limit of propane... so the only thing I can think is that during compression, the fuel and air are squished into a much smaller area, effectively raising the concentration of fuel per volume air, and thus bringing it into its flammability range.

As for the difference in combustion temperature, a propane flame burns at ~3596F, gasoline at ~1508F (of course, dependent upon intake air temperature and compression ratio, but from what I can find online, those numbers are typical). So the propane burning hotter would give greater thermal expansion of the air in the cylinder, thus more cylinder pressure.

But according to:
https://in.answers.yahoo.com/questio...7125444AA6w7wz
"We ran taxicabs on propane for many years. The problem is lower fuel mileage (about 15% +/-)."

So apparently the higher combustion temperature isn't enough to offset the lower energy content of propane vs. gasoline. Which makes it hard to believe it would have a higher BTU/mile in the first place.
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Old 04-26-2015, 02:06 AM   #66 (permalink)
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Quote:
Originally Posted by Cycle View Post
So that observed 5% difference in BTU/mile fuel efficiency may just be because propane burns leaner than gasoline.
Sense OEM gasoline ICEs have run up to 25:1 Lean Burn ... I doubt (haven't seen documentation supporting) that any further leaner would yield any significant (measurable) benefit (ie the 5%) in BTU/mile .. or in raw BTU/BTU energy efficiency.

Quote:
Originally Posted by Cycle View Post
But that's only 1.3548% fuel to air by volume
No.
A 5% improvement in BTU/mile does not itself tell you what the AFR was ... Only that is was in the range to still allow the engine to function.

Quote:
Originally Posted by Cycle View Post
So the propane burning hotter would give greater thermal expansion of the air in the cylinder, thus more cylinder pressure.
Always boils down the energy (BTU) ... which is the capacity to do work .. ie move the piston ... or move the air .. change the temperature of the air .. or move the car.... etc.

Changes in temperature without changes in the energy content (BTU) will not change the total capacity to do work ... even heating the air type of work.

Quote:
Originally Posted by Cycle View Post
Which makes it hard to believe it would have a higher BTU/mile in the first place.
Feel free to ask him for his records / references ... I'd suggest doing so nicely .. 'more flies with honey' as the saying goes.
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Old 05-22-2015, 12:02 PM   #67 (permalink)
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This sounds strangely like the Smokey Yunick Pontiac Fiero concept from the 1980's. I've seen a couple of dyno runs abot it a few years back.
What Ever Happened To Smokey's Hot-Vapor Engine? - Hot Rod Magazine
Looked legitimate back then, but it all comes back to emissions.
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Old 05-22-2015, 01:36 PM   #68 (permalink)
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Quote:
Originally Posted by IamIan View Post
I'll try again.
I admire your perseverance.

Quite frankly I'm sorry we don't see more references to BTU/mi or BTU/km in comparisons, both engine-to-engine and car-to-car. It might show more people the cost of the choices they make - though really it's generally nerds like us that are seriously interested in such details.
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Old 06-16-2015, 03:09 AM   #69 (permalink)
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Part of the reason i got looking into this is i was looking at how the fuel ratio's affected the combustion temperature in a car. What i found out is that when you lean out the car it burns hotter, and when you rich the mixture it cools down right.

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Like the chart above shows. however I then saw a chart that shows the temperature rise of gasoline and how hot it gets to the amount of fuel used.

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Like this! (ofcourse this is the wrong one but i'm trying to make a point!) It showed that the heat produced increases with the amount of fuel added(obviously!!). But then why does a combustion engine burn hotter when the ratio is reduced rather then when it's raised?? The answer I came up with is that the amount of fuel added is much higher then air. Imagine the chart i have above showing the temperature of the fuel as air is removed.

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About like this chart. then the temperature drops when more fuel is added or more air is taken away. I feel that this is a aspect of internal combustion engines that we don't take into account when thinking about fuel to air ratios. We worry too much about the schoimetric ratio and stuff like that that we don't look at how the air to fuel ratio in that internal combustion engine should really be. Meaning that if you add more fuel the temperature rises, and when you add less fuel the temperature drops. I really wonder just how far off internal combustion engines are if my charts above are truly "accurate" like i believe they are.

p.s if someone can find a chart like the last two i posted but for gasoline i would really appreciate it if you would post it for me here. I've been looking for it for days now but all i find are stupid charts about climate change to gasoline burning ratios and rates.
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Old 06-16-2015, 03:57 AM   #70 (permalink)
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I think the point here is that if propane gets 5% better economy than gasoline, and gasoline has 36% more energy than propane, it's obvious that if you evaporate gasoline you get something equivalent to propane, only that much more of it.

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