Date:         Sun, 25 Nov 2007 08:19:40 -0800
Reply-To:     John Bange <jbange@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         John Bange <jbange@GMAIL.COM>
Subject:      Re: Calculate fuel consumption when idling?
Comments: To: Michael Elliott <camping.elliott@gmail.com>
In-Reply-To:  <47499C41.6010509@gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

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"