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

[MRS954@xxxxxxx]

 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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