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  1. #1

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    Default Diesel fuel evaporation

    I have a rookie question. It seems when you spill diesel fuel it doesnít evaporate like gasoline. Like when I fill up the fuel tank. If some fuel spills on the paint and I donít wipe it it stayís wet until I wipe it maybe a few days later. Is this because of the higher oil content in diesel [img]/forums/images/graemlins/confused.gif[/img] [img]/forums/images/graemlins/confused.gif[/img]

  2. #2
    Gold Member TMcD_in_MI's Avatar
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    Default Re: Diesel fuel evaporation

    </font><font color="blue" class="small">( I have a rookie question. It seems when you spill diesel fuel it doesnít evaporate like gasoline. Like when I fill up the fuel tank. If some fuel spills on the paint and I donít wipe it it stayís wet until I wipe it maybe a few days later. Is this because of the higher oil content in diesel [img]/forums/images/graemlins/confused.gif[/img] [img]/forums/images/graemlins/confused.gif[/img] )</font>

    Sort of. Crude petroleum is made of hundreds of different compounds. Some of them have low boiling temperatures and evaporate easily. These are what you can find in gasoline. Others evaporate less easily and are used in kerosene, jet fuel, and diesel fuel, for example. They are thicker and feel a bit oilier. Still others evaporate very poorly and are oilier yet. We use those as lubes and call them oils. And then there are greases and tars.


    So to answer your question, it's not that diesel has a higher oil content, but that it's made of compounds that have oilier properties than gasoline. Oil itself is a different range of compounds, although I suppose you could think of diesel as a very very light weight oil.

    There are a lot more details to all this, but I hope this is an OK answer to your question.

    Tom

  3. #3
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    Default Re: Diesel fuel evaporation

    Going from memory here...IIRC, the vaporization temperature of #2 is something like 140F at amospheric pressure, so below that temperature it's going to take a LONG time to evaporate.

    That's the primary reason that diesel has a longer shelf life than gasoline.

  4. #4
    Gold Member TMcD_in_MI's Avatar
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    Default Re: Diesel fuel evaporation

    </font><font color="blue" class="small">( Going from memory here...IIRC, the vaporization temperature of #2 is something like 140F at amospheric pressure, so below that temperature it's going to take a LONG time to evaporate. )</font>

    cp1969, I guess I'm not familiar with the term 'vaporization temperature'. Maybe it seems like a dumb question, but could you explain what that is?

    Tom

  5. #5
    Elite Member SkyPup's Avatar
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    Default Re: Diesel fuel evaporation

    Different petrochemicals have different densties (the specific gravity of the substances vary), this causes the vapor pressure to vary as well. Lower density mixtures of hydrocarbons have a higher vapor pressure and higher density mixtures of hydrocarbons have a lower vapor pressure.

    The vapor pressure is the amount of molecules that are vaporized at a given temperature, heating up the molecules increases the vaporization of the substance. Just like heating up water molecules, the molecules go from the liquid to gas state more rapidly as the temperature increases.

  6. #6
    Gold Member TMcD_in_MI's Avatar
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    Default Re: Diesel fuel evaporation

    <font color="blue"> The vapor pressure is the amount of molecules that are vaporized at a given temperature, heating up the molecules increases the vaporization of the substance. </font>

    Thanks for taking a shot at answering my question, Skypup, but cp1969 had referred to something he called "vaporization temperature" and it was this term I was asking about. I'm OK with vapor pressure, but I'm not sure exactly what vaporization temperature might be.

    Tom

  7. #7
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    Default Re: Diesel fuel evaporation

    vaporization temperature = boiling point

  8. #8
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    Default Re: Diesel fuel evaporation

    Vaporization temperature.

    Probably the wrong terminology. What I was referring to is the point at which diesel begins to readily evaporate. IIRC, that is around +140F at atmospheric pressure, as compared to -70F for gasoline.

  9. #9
    Gold Member TMcD_in_MI's Avatar
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    Default Re: Diesel fuel evaporation

    </font><font color="blue" class="small">( What I was referring to is the point at which diesel begins to readily evaporate. IIRC, that is around +140F at atmospheric pressure, as compared to -70F for gasoline. )</font>

    Thanks cp1969. What confuses me is this: My understanding is that all liquids are constantly vaporizing, although some incredibly slowly, and the hotter they get, the faster they vaporize. So the idea of having a particular temperature that would be called the vaporization temperature sounded a little odd to me. I thought maybe there was some way that it was defined that I didn't know about and was just interested to know what that might be.

    MikePA - Thanks for your answer. If vaporization temperature = boiling point, that would be a definition of boiling point that I've never seen. I believe that boiling point is usually defined as the temperature at which the vapor pressure of the liquid equals atmospheric pressure.

    Anyway, I'm being guilty of hijacking the thread, and prolonging a discussion that doesn't have much to do with tractors. Sorry.

    Thanks to all who responded.

    With all respect.

    Tom

  10. #10
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    Default Re: Diesel fuel evaporation

    I wouldn't see how you're hijacking the thread, since it's title is, after all, Diesel fuel evaporation.

    You're right about liquids vaporizing all the time as a function of temperature. Obviously that is the case or we wouldn't be able to smell diesel at normal temps and pressures for humans. Not that the lack of odor proves something is NOT evaporating, but the presence of an odor, I think, proves that it is.

    But there is something special about diesel and 140F. I can't find anything to support this, but, from fuel hauling days, we were required to do vapor recovery when filling gasoline tanks, but not when filling diesel tanks. The air in a diesel tank was considered to be 'air' and not vaporized diesel. I wouldn't want to make a habit of breathing it regularly, but it must have been considered non-flammable and non-polluting or the EPA and OSHA would have been all over it.

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