[Cycle]

Originally Posted by IamIan

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.