Date:         Sun, 25 Nov 2007 08:29:33 -0800
Reply-To:     Michael Elliott <camping.elliott@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Michael Elliott <camping.elliott@GMAIL.COM>
Subject:      Re: Calculate fuel consumption when idling?
Comments: To: John Bange <jbange@gmail.com>
In-Reply-To:  <6da579340711250819n3d526bc6i6203d245a1e14c50@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

I somehow suspect you're messing with me here. But I'll bite: the ECU
works to keep the O2 sensor happy, which means that the mixture is close
to stoichiometric, meaning roughly 1:15 fuel to air mass ratio; and the
duty cycle needed to accomplish this is irrelevant. The bottom line is
that for every gram of air, we use one-fifteenth that in fuel. Roughly. If
I even have a clue. I never took auto shop. Those were the tough guys,
tattooed, smoking cigarettes behind the building, greasy fingernails.
Liked to beat up on little guys like me.

--
Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano
KG6RCR



On 11/25/2007 8:19 AM John Bange wrote:

> I don't think you've spent quite enough time on this. You need to tell
> us what the duty cycle of the injectors is at idle now.
>
>
>     Each piston will still suck in 475 cc of air/fuel per intake cycle. But
>     instead of the air being at normal atmospheric pressure, it sucks on the
>     intake manifold/plenum, which is at around 11'' Hg of vacuum, or
>     11'' Hg
>     less than the outside air pressure (Bentley's does not come right
>     out and
>     say that 11'' Hg is the normal vacuum inside the plenum but it can be
>     inferred from from several of their measurement procedures). Mean sea
>     level pressure is about 30'' Hg, so the plenum contains 19'' Hg of
>     pressure, which is about the same as being at 12,000 feet elevation
>     according to the online Density Altitude Calculator at
>     http://wahiduddin.net/calc/calc_da.htm -- if I'm using it right. 70F,
>     30''Hg altimeter setting, 40F dew point.
>
>     Under these conditions, air density is 62% of sea level air. So my
>     Junior
>     Engineer's cocktail napkin result of 1.6 gallons per hour of fuel
>     consumption when idling (below) needs to be reduced to 1 gallon per
>     hour.
>
>
> --
> John Bange
> '90 Vanagon - "Geldsauger"