RE: [Chrysler300] New question on fuel tank sending units

["Bob Jasinski" <rpjasin@xxxxxxxxxxx>]

Mark,
 
Thanks for the feedback, that makes a lot of sense.  Evidently there is
never enough oxygen to sustain or allow the burn inside the enclosed tank,
even when it is near empty.  I did once see a guy put out a lit cigarette in
a small pan of gas outside in a controlled setting on a bet that it would
not burn.  He actually dropped (quickly) the lit cigarette into the gas and
nothing happened except to extinguish it.
 
Bob J
PS: don't try this at home!

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From: mrs954@xxxxxxx [mailto:mrs954@xxxxxxx] 
Sent: Friday, December 28, 2007 1:27 PM
To: rpjasin@xxxxxxxxxxx; Chrysler300@xxxxxxxxxxxxxxx
Subject: Re: [Chrysler300] New question on fuel tank sending units


Bob,
>From a firefighter's point of view, I don't think there is the correct
air-fuel mixture inside the closed gas tank to support combustion. There is
such a high concentration of fuel vapor above the surface of the gasoline,
also known as "rich" that the gasoline won't ignite. You need a lot of fresh
air that has at least 16% oxygen content to support the combustion. In
addition, petroleum products do not conduct electricity, therefore the
sending unit needs an external ground. You've probably heard this before,
but gasoline does not burn or explode. What burns is the vapor coming off
the surface of the liquid as it mixes with air. That vapor is actually
gasoline and air mixed together. You can take a dish of gasoline and toss a
match into it and it will rapidly burn, or seemingly explode.  What's
happening is the vapors igniting, and the heat generated draws the vapor up
off the surface so rapidly that it creates more vapor and thus burns that
vapor. Don't try this at home, but if you place a dish of gasoline on your
driveway on a windy day, you can throw a lit match into it and it won't
burn, the match will be extinguished by the gasoline liquid.  This is
because the wind is blowing the vapor away too quickly for the match to
ignite it.  
The function of the carburetor is to do just that. It mixes a little liquid
with a lot of air to create the volatile substance which is drawn into the
cylinder for ignition.


Regards,
Mark Souders



-----Original Message-----
From: Bob Jasinski <rpjasin@xxxxxxxxxxx>
To: chrysler300@xxxxxxxxxxxxxxx
Sent: Fri, 28 Dec 2007 3:56 pm
Subject: [Chrysler300] New question on fuel tank sending units


Since we're on the subject of fuel tank sending units, I thought I'd ask a


question that's been bugging me for years.  How is it that electric fuel


sending units are safe to use inside of a fuel tank?  Here we have a device


that has a voltage applied and conducts current through a sliding resistance


setup connected to a float.  It seems to me that it would be quite possible


for a spark to occur and ignite the gas vapors, yet I've never heard of that


happening.  What am I missing here?  Certainly there is oxygen within the


tank along with gas vapors, so the sending unit acting as the ignition


source could complete the fire triangle, but I've never heard of a problem,


even if the sending unit fails.  Any thoughts on this folks?


 


Bob J









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