Hybrid Car – More Fun with Less Gas

Vehicle Gas Consumption - Accurate? - Page 14

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Posted by Al Falfa on May 12, 2012, 12:30 am
"Elmo P. Shagnasty"  wrote in message

yeah, keep telling yourself that.

In the meantime, I will continue to buy specific volumes of fuel at
specific prices and have that fuel propel me a specific number of miles
down the road, and will be able to calculate (a) my number of miles per
gallon, and (b) my fuel price per mile--

--all without knowing OR CARING about the fuel chemistry.

Again, the numbers I calculate will *reflect* the fuel chemistry, but no
one needs to know the fuel chemistry in order to calculate those numbers.

Your insistence on calling that "wrong" tells me you're not paying

OK, look at it this way.  You buy 1 gallon of fuel A and go 50 miles.  You
buy 1 gallon of fuel B and go 49 miles.   Oh, wait, you are right.  The
energy content doesn't matter.

Posted by Al Falfa on May 12, 2012, 12:24 am
"Elmo P. Shagnasty"  wrote in message

So far so good.

It's not "calibrated" to anything like that.

An injector pulses X amount of gas.  X times the number of injector
pulses is the total gasoline used.  Calculate that against the miles
driven in that number of injector pulses.

This is just a fancy engine computer calculated version of the very same
thing people do when they calculate their mileage at the pump based on
how much gas they put in the tank and how many miles they drove since
the last fillup.

The energy content of the fuel is *reflected* in the final calculation,
but it is not *part* of the calculation.  It used THIS much gas, and
drove THAT many miles--period.  Lower energy content fuel will deliver
fewer miles per volume, regardless of whether you're measuring it at the
pump or the engine computer is measuring it at the injector.


The X amount of gas to which you refer will drive the piston with a force
related to it's energy content.  If it is E10, with a lower energy content,
it will take more gas to do the same work.

My point is that Toyota doesn't know the energy content of the gas they
meter, hence a small error is inevitable.

Posted by Elmo P. Shagnasty on May 12, 2012, 1:46 am

Exactly correct--and yet meaningless to the calculation of "how many
miles can I drive on X gallons of the fuel that I put in the tank".

I get a number, and yes, fuels with lower energy content will show lower
numbers.  As I said, the final calculated number will REFLECT the
varying energy content, but the energy content itself does not factor
into the calculation of the final number.

My point is that they don't have to, any more than the driver has to
know the energy content of the gas as he sits in his car after filling
up and calculates "I drove X miles on Y gallons of gas, I got Z miles
per gallon".

Posted by Elmo P. Shagnasty on May 15, 2012, 2:58 am
 In article

And, of course, the real problem is that people are calculating their
mileage at various pumps at various stations at various times of
day--which is inherently less than accurate.

Posted by Michael Dobony on June 17, 2012, 5:41 pm
 On Wed, 9 May 2012 00:32:59 -0500, Al Falfa wrote:

That is a contradiction. One gallon of 87 octane is the same volume as 87
E10 and the same volume as 89 octane. The octane does not change what a
gallon is.

OTOH, I am not convinced that the gallon count on the pump is accurate. I
filled a 5 gallon can with over 5.25 gallons and it already had some gas in
it. I strongly suspect that many pumps, verified or not, are charging for
inflated gallon figures.

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