Mileage calcs

[Marteney, Steven J.]

That's very interesting, hadn't heard that.  So, high vacuum in the intake
means less resistance to the fuel spray so more comes out.  HOWEVER, the
regulator at high vacuum reduces the fuel pressure so less comes out,
therefore compensating???  So, rating 22lb/hr injectors always at 22lb/hr is
the right way???  I know I've read, here I believe, to use the square root
of the operating pressure div by the rated pressure to adjust the flow rate.

Steve

-----Original Message-----
From: Bob Valentine [mailto:bob at tecmark.com]
Sent: Friday, June 15, 2001 10:13 PM
To: gmecm at diy-efi.org
Subject: RE: Mileage calcs


Isn't the vacuum referenced FPR to account for the fact that the business
end of the injector is exposed to intake vacuum, which would affect the
flow rating if not compensated for?  That's my understanding as to why TBI
units don't have a vacuum referenced FPR.

-> Bob Valentine
-> bob at tecmark.com

At 12:13 PM 6/11/2001 -0400, you wrote:
>Don't forget about vacuum controlled fuel pressure regulators.  One
>typically sets pressure for WOT (engine off of course) but on the road fuel
>pressures are ~5psi less.  Makes a >.5 change in my AFR calcs.
>
>Steve
>
>-----Original Message-----
>From: David Papworth [mailto:papworth at ichips.intel.com]
>Sent: Monday, June 11, 2001 11:10 AM
>To: gmecm at diy-efi.org
>Subject: Re: Mileage calcs
>
>
>Gasoline is a mixture of a number of hydrocarbons without rigidly
>fixed properties. One source gives an "as delivered" density range
>from 640 to 780 kg/m(3), with a mean of 730.
>
>There are 2.2 pounds per kilogram and 264 gallons in a cubic meter.
>So that gives us 5.3 to 6.5 pounds per gallon, with a mean of 6.08.
>The same source:
>http://www.users.qwest.net/~taaaz/AZgas.html
>points out that retail gasoline pumps are only accurate to +/- 0.5 percent
>and that the density of gasoline drops by 2% at 90 degrees vs. a
>"standard delivery temperature" of 60 degrees.
>
>As a check, I know that 100LL aviation gasoline was historically figured at
>5.83 lbs per gallon, with most flight instructors urging their students
> to "use 6 lbs per gallon" when doing a weight-and-balance calculation.
>
> The density of auto gas has crept up over the last 6 years or so, as the
>more volatile
>components have been removed to help in the reduction of urban VOC. Ethanol
>comes in at 789 kg/m(3) -- 6.6 lbs per gallon -- so 10% gasohol fuel would
>have
>a mean density of 6.13 lbs per gallon. MTBE, on the other hand, is 740
>kg/m(3);
>close enough to the mean of gasoline to have a negligible effect on
density.
>
>So a figure of 6.0 to 6.1 lbs per gallon seems like a reasonable starting
>point. It looks to me like getting +/- 0.5 "mile per gallon" accuracy
>out of a calculation based on weight is about as good as it ever will get,
>given the variable density, temperature issues, and gas pump inaccuracy.
>
>When you think about it, volume is simply not an accurate measure
>for a chemical like gasoline. Weight would be much better --
>and more reflective of the value (energy content)
>of what you are buying.
>
>This brings up the question of the accuracy of taking the ECM's idea of
>how much fuel is being used as the input to an MPG totalizer. The
>ECM cannot know about evaporative losses not recovered
>by the carbon cannister, or recovered during open-loop operation.
>
>If the 9th injector is used in your setup, the ECM does not know how much
>fuel is used for starting. These two factors would tend to make an MPG
>calculation read higher than reality.
>
>Open loop operation is accurate only to the extent that the fuel pump
>pressure is accurate and constant. As the injectors wear, they probably
>flow a little more at a given pulse width, so open loop operation gradually
>enrichens over time -- the ECM doesn't really "know" how much fuel
>the engine is getting without feedback. Again, your calculation will come
>out too high.
>
>I would think you could get very accurate instantaneous MPG readouts
>while the ECM is in closed-loop mode, assuming you take the BLM
>counts into account. Just integrating the grams/second number off the MAF
>and assuming stoichiometric operation might do it. But a long-term
>total miles per gallon calculation, including the effects of starting,
>open-loop,
>and evaporative losses seems more challenging.
>
>It's an interesting project -- what kind of accuracy are you actually
>seeing?
>
>
>
>----- Original Message -----
>From: "Gabe" <gellett at earthlink.net>
>To: <gmecm at diy-efi.org>
>Sent: Sunday, June 10, 2001 3:10 PM
>Subject: Mileage calcs
>
>
>> Doing some MPG calcs..  Going to play around with calculating MPG from
the
>> output of my 165 ECM...  Need to know what the weight of a typical gallon
>of
>> pump gasoline is (or a lb/hr to GPH conversion), and any other tips
anyone
>> has...
>>
>> So far I've found 6.1 lbs/gal on the web - anyone have a more precise
>> measurement or come up with different numbers?  My calcs with this factor
>seem a
>> bit liberal...
>>
>> Thanks
>> Gabe
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