Vapour Injected LPG

[Joe Chiasson]

Joe, Tony, GT and Justin by my opinion you are all correct.  It would be
more advantageous to inject as a liquid.  For the most part at normal
operating temperatures the lp would all vapourize in the cylinder before
the spark.  The deal is since this expansion is happening in the cylinder
it displaces more air than if vapourizing before injecting.  Also the
sudden expansion in the cylinder does significantly reduce the temperature.
 On a mass flow basis when compared to gasoline injecting liquid into the
cylinder will net you 5-10% more horse power, and vapour injection will
loose 10-15% horse power.   From a cost factor liquid is a lot more
expensive because of a need for a pump wether it be internal to the
cylinder or external (internal seems to work a lot better). Without a pump 
the lp suddenly expands to vapour at the tip of the injector freeezing it,
with a pump depending on the spray patern of the injector you can get a
nice pencil stream of liquid as it gradually expands to vapour.   
Joe from my experience I'm gonna have to say that this guy in his checy may
have had the old injector(s) and fuel rail present but he was running the
engine on vapour propane through the air horn (if this was an actual
conversion or was he just playing around with lp I may have misinterpreted
your mail).  If however he has injecting liquid through the stock gasoline
rail and injector(s) I would have to question how many vapour bubbles were
present in the fuel after passing through the fuel rail regulator, I would
have to question what temperature he was doing this at, and have to
question after he shut it off how long did he have to sit before he could
get the thing started again?
----------
> From: Justin Albury <jalbury at tpgi.com.au>
> To: diy_efi at efi332.eng.ohio-state.edu
> Subject: Re: Vapour Injected LPG
> Date: Monday, January 12, 1998 5:37 PM
> 
> Joe Boucher wrote:
> > 
> > I don't understand why expanding lpg to a gas before injecting it would
> > give big advantages.  In the elevated temperatures of a working engine,
> > even at high engine speeds , by the time the spark plug fires during
the
> > compression storke, lpg injected as a liguid would be completely
changed
> > to a gas.
> > 
> > I haven't done a thermal analysis of this situation, but I think it's a
> > good quess.
> > 
> > Joe Boucher
> > '70 RS/SS Camaro  '81 TBI Suburban
> 
> 
> cost factor!
> 
> think about it.... both my cars are delco efi & lpg......with vapour lpg
> i dont need a fuel pump in the lpg cylinder and im not running high line
> pressures in the engine bay.  so apart from that i love the thought of
> liquid injection but the tanks with pumps in em are very$$$$$$...that is
> unless you guys in the states run a different system ....say  take the
> lpg into the engine bay at tank pressure then regulate it to a lower
> pressure which even when the tank is low it will still give good
> pressure then inject it .......all i seem to have happen is injectors
> freezing .......ummm i spose you get that with lpg eh!???
> 
> any thoughts??
> 
> Justin