Resulting vapor pressure from hydrocarbon mixing

[servaas]

I'm working on a (automotive) system whereby a mixing will take place between roughly 5CC of LPG (say: Propane in liquid state) and 50 CC of Gasoline(also assume liquid state).

Question is here: can I somehow calculate/estimate the resulting vapor pressure?

Background is that I Do not know if there is ideal mixing taking place between these two constituents but I have this idea that somehow a certain level of dilution of the LPG with gasoline should reduce the resulting vapor pressure of the mixture to a value below the max pressure head that the gasoline pump can deliver. If so; the gasoline fuel pump will be able to "take over" the fuelling and feed the gasoline into the high pressure pump(which was originally primed with LPG) mounted onto the engine.

I try to come up with a robust solution for "replacing" some 5CC of LPG inside a high pressure fuel pump's inlet tract with a fresh supply of gasoline whereby the maximum Gasoline pressure head(from gasoline low pressure pump) available is some 5 bar. See my problem?


i would be most grateful for any suggestions.

greetings, Servaas.

 

[IFRs]

Rault's law?

 

[servaas]

yes, Raoult's law should apply as fas as I can see. Thing is that I have no clue how close you have to get to ideal mixing in order to make valid use of this law.

greetings, Servaas.

 

[MortenA]

Vapour pressure is temperature dependant.

You need to know/consider the final temperature of the mix.

When the LPG is in the liquid state it will (normally) be at its boiling point at one atm. Once you mix it with the gasoline you have another temperature - the vapour pressure will then depen on the final composition AND temperature.

If you know composiotn and use a process simulator then you could get a faily accurate number up front - else - try it out.

Best regards

Morten

 

[dcasto]

lpg vapour pressure is 208, gasoline is about 14. 5/55 * 208 + 50/55 * 15 = 32 psi at 100 F.
The problem is the liquid lpg is going to have 10 to 15 bar pressure on the suction to the pump, the gasoline pump will to overcome that presure