Diesel fuel evaporation

kevinj · Sep 29, 2005

I was in the fuel biz a few years back too. I think the term is "flash point" but I can't find my book to see what the number is. I do remember that fuel oil was "high flash" and gas was "low flash" In the boiler biz we deal with flash point and fire point with flash being the vapor temp and fire being the temp to sustain combustion on its own.

KJ

1962 · Sep 29, 2005

The flash point of diesel fuel is 100 deg. F. for type 1-D fuel. And 125 deg. F. for type 2-D fuel. And 130 deg. F for type 4-D fuel.

kevinj · Sep 30, 2005

Thanks for the info. At flash point you end up with enough evaporation or vapor to create a flash fire. I hope this answers the posters question about the temperature relation to evaporation.

DanMan1 · Oct 1, 2005

(
The vapor pressure is the amount of molecules that are vaporized at a given temperature,. )

Something doesn't look right here. If the term is 'vapor pressure ' then I would assume the number would be a 'pressure' number such as 'mm Hg' or 'atm' etc.., not a count of how many molecules?

SteveInMD · Oct 1, 2005

Diesel is a mix of many many compounds. When you spill some on your tractor the more volatile compounds partition into the air leaving behind the less volatile compounds. The hotter it is the more compounds will evaporate. Gasoline is also a mix of many compounds virtually all of which evaporate at normal outdoor temperatures.

Boiling point and vapor pressure are both valid terms here.

Vapor pressure describes the how easily the molecules go from a liquid to a gas (or evaporate). In liquid form the molecules of some compounds are more strongly attracted to each other than in others. If you put the same amount of two different liquids in two containers that are the same size and at the same temperature, then measure the pressure inside the containers, they will be different. The vapor pressure will be different because the number of molecules of gas above the liquid will be different (PV=nRT), mostly due to the difference in the intermolecular forces in each liquid.

PV = nRT is the "Ideal Gas Law"

Pressure x Volume = number of molecules x The Gas Constant x Temperature.

TMcD_in_MI · Oct 1, 2005

( (
The vapor pressure is the amount of molecules that are vaporized at a given temperature,. )

Something doesn't look right here. If the term is 'vapor pressure ' then I would assume the number would be a 'pressure' number such as 'mm Hg' or 'atm' etc.., not a count of how many molecules? )

You are of course right DanMan. In SkyPup's defense, a problem with this forum is that it's hard to know how technical to be with our terminology and explanations. If this were a chemistry forum, it would be a little different.

Tom

SteveInMD · Oct 1, 2005

( Something doesn't look right here. If the term is 'vapor pressure ' then I would assume the number would be a 'pressure' number such as 'mm Hg' or 'atm' etc.., not a count of how many molecules? )

Actually the term "Pressure" and "count of how many molecules" are pretty much the same thing here. More molecules in the gas is another way to say "more pressure" (at a given temperature). Pressure is simply a measurement of how many gas molecules collide with a given surface area at a moment in time.

Sorry if all that was too much chemistry. As to the original question, I'll try again ...

Diesel is made of a lot of stuff. Some evaporates easily. The stuff that doesn't is what's left on your tractor a few days after you spill it.

As far as gasoline goes, almost all of the stuff that makes up gasoline evaporates easily.

TMcD_in_MI · Oct 1, 2005

Diesel is made of a lot of stuff. Some evaporates easily. The stuff that doesn't is what's left on your tractor a few days after you spill it.

As far as gasoline goes, almost all of the stuff that makes up gasoline evaporates easily. 

Hey SteveInMD, I think you've got it! /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif

Seriously, if it sounded like I was complaining about the chemistry content, then I didn't communicate very well. I was just making a general comment about the nature of the group, although at this point in the thread, I'm guessing that we have been tuned out by the majority of readers. I speak chemistry, so you won't get a complaint out of me. Sorry if it sounded like it.

Tom