Date: Sun, 25 Nov 2007 08:01:05 -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?
In-Reply-To: <005601c82f3a$24089510$0a00080a@NewHomeHub>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Hmmm.
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.
--
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 12:06 AM John Connolly, Aircooled.Net wrote:
> but we have a throttle limiting the amt of air entering the engine (unless
> you have a diesel).
>
> John
> Aircooled.Net Inc.
>
> ----- Original Message -----
> From: "mike elliott" <camping.elliott@GMAIL.COM>
> To: <vanagon@GERRY.VANAGON.COM>
> Sent: Saturday, November 24, 2007 5:26 PM
> Subject: Re: Calculate fuel consumption when idling?
>
>
>> Do you win? Heck, I don't know. I'll take a shot at it. Watch me get
>> it spectacularly wrong.
>>
>> The 1.9L engine has 475cc displacement per cylinder. I think two
>> cylinders fire per revolution, so at 900 rpm we got 900 x 2 x 475 =
>> 855cc of air per minute being sucked into the engine. If the mixture
>> is a good stoichiometric one, we'd have about a 1:15 fuel:air mass
>> ratio. Air has a mass of 1.3g per liter, so that's .855 x 1.3 = 1.1kg
>> of air per minute, with being one-fifteenth of that, or 74g per
>> minute. At 60 minutes that's 4.4kg of fuel. Gasoline masses roughly
>> 740 grams per /liter, so that's 6 liters, roughly 1.6 gallons U.S. per
>> hour.
>>
>> Those are the numbers I come up with and I bet they're within an order
>> of magnitude of being right.
>>
>> Mike "Rocket J Squirrel" Elliott
>>
>> On Nov 24, 2007 3:52 PM, Matthew Snook <matt@snooksband.com> wrote:
>>> 0.9375? Is that right? Do I win?
>>>
>>> :)
>>>
>>> At 60mph, mine's turning @ 3200rpm. It will burn 3 gallons doing that.
> 3
>>> gallons per hour at 3200rpm. But it idles at 1000rpm. So that comes to
>>> 0.9375 gallons per hour at 1000rpm. Of course there's no wind
> resistance at
>>> that speed, so maybe less...
>>>
>>> Matthew Snook (@ ~3000 ft)
>>>
>>>
>>>
>>> -----Original Message-----
>>> From: Michael Elliott
>>> Subject: Calculate fuel consumption when idling?
>>>
>>> A properly-tuned 1.9L WBX engine would consume how many gallons of
>>> gasoline per hour when idling at sea level? Would this be significantly
>>> different at 6,000 feet?
>>>
>>>
>> !DSPAM:4748b1c081151569112627!
>>
>>
>
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