Does half a tank of 87 octane plus half a tank of 91 = a full tank of 89?
04-25-2011, 06:01 PM
#13
Join Date: Oct 2010
Location: CT
Posts: 37
Figured I would do a quick introduction to analytical chemistry here.
In a vacuum 1000 lbs of lead = 1000 lbs of feathers… but we don’t live in a vacuum do we? In analytical chemistry when high precision is required (via a balance or scale) you must factor in the difference in density between the scales internal balance and the item being weighed. Why? Simple, because a scale can only accurately measure the mass of an object that has the same density as the scales ‘internal calibration mass’.
In lay mans terms this means that if the scale used a brass internal weight the scale can only accurately measure the weight of brass. Any object you try to weigh with a lower density will give you a false low reading. Any object you try to weigh with a higher density will give you a false high reading. In chemistry when high precision is required we have to account for this.
So it is very likely that the density of lead is higher than a scales internal balance and the density of a feather is much less than the internal balance. Therefore if you were to put 1000lbs of lead into a box of neglectable mass and 1000lbs of feathers into a box of neglectable mass then weigh each box in a vacuum to give the true mass you would see that you had less than 1000 lbs of lead and more than 1000lbs of feathers. The feathers weight more.
also according to wikipedia (which isn’t always accurate)
it would seam that you could say 1/2 tank of 87 and 1/2 tank of 91 should be equivalent to (87+91)/2=89. But i highly doubt this is accurate. I’m sure there has to be some interaction in-between the different fuels that would effect the octane rating. I’m sure if you were to dig through some science books you could find a real answer but for sake of conversation I would just assume that 87 +91 = ~89 octane.
In a vacuum 1000 lbs of lead = 1000 lbs of feathers… but we don’t live in a vacuum do we? In analytical chemistry when high precision is required (via a balance or scale) you must factor in the difference in density between the scales internal balance and the item being weighed. Why? Simple, because a scale can only accurately measure the mass of an object that has the same density as the scales ‘internal calibration mass’.
In lay mans terms this means that if the scale used a brass internal weight the scale can only accurately measure the weight of brass. Any object you try to weigh with a lower density will give you a false low reading. Any object you try to weigh with a higher density will give you a false high reading. In chemistry when high precision is required we have to account for this.
So it is very likely that the density of lead is higher than a scales internal balance and the density of a feather is much less than the internal balance. Therefore if you were to put 1000lbs of lead into a box of neglectable mass and 1000lbs of feathers into a box of neglectable mass then weigh each box in a vacuum to give the true mass you would see that you had less than 1000 lbs of lead and more than 1000lbs of feathers. The feathers weight more.
also according to wikipedia (which isn’t always accurate)
The octane number of a fuel is measured in a test engine, and is defined by comparison with the mixture of 2,2,4-trimethylpentane (iso-octane) and heptane which would have the same anti-knocking capacity as the fuel under test: the percentage, by volume, of 2,2,4-trimethylpentane in that mixture is the octane number of the fuel. For example, petrol with the same knocking characteristics as a mixture of 90% iso-octane and 10% heptane would have an octane rating of 90.[1] This does not mean that the petrol contains just iso-octane and heptane in these proportions, but that it has the same detonation resistance properties. Because some fuels are more knock-resistant than iso-octane, the definition has been extended to allow for octane numbers higher than 100
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