Propane injection (was Nitrus injectors (was Hydrothermal

[Raymond C Drouillard]

On Thu, 18 Jun 1998 08:30:48 -0500 "Joe Chiasson" <chiasson at hutchtel.net>
writes:
>> Someone posted a URL about injecting liquid propane.  They didn't give
>> too many details.  They implied that the propane was injected really
>> close to the intake valve.  On my AMC 360 engine (Jeep Grand
Wagoneer), I
>> would probablly end up injecting it right under the present throttle
>> body.  This would give it time to completely evaporate and get well
mixed
>> with the air.
>
>>From my point of view, injecting liquid anywhere besides right over the
>intake valve has no advantages.  Injecting over the intake valve you
cool
>the valve, you vapourize less before entering the combustion chamber =
more
>power.  Liquid propane has more energy per pound than gasoline, vapour
>propane less.   Injecting under the throttle all the liquid will be
>vapourized before entering the cylinders thus all the inherent
advantages
>of the liquid are gone.  Therefor it dosent make any sense to go through
>the heartaches of makeing a liquid system work (if you are going to
inject
>it near or into the throttle body).

One of the advantages of the injection of gasoline near the port is that
more of it enters the cylinder as a liquid.  That is not, however, what I
am trying to achieve with liquid propane.

First of all, the propane is going to vaporize so quickly once it hits
the low atmospheric pressure that trying to get it into the cylinder as a
liquid would be difficult.

Secondly, it isn't necessary, or even desirable.  As the propane
vaporizes, it absorbs heat from the air.  This decrease in temperature
will cause it to be more dense, allowing more to be sucked into the
cylinder.  Many engines use cold air intakes and intercoolers for this
reason.

What I want to calculate is how big this effect will be.  Will the heat
absorbed by the propane make the intake charge dense enough to compensate
for the 3-4% extra volume that is contributed by the propane?  When I get
the constants and the one formula that I need, I will be able to figure
this out.

At any rate, injecting it as a liquid will cool the intake charge
somewhat, giving a performance advantage over a system that uses a
propane mixer.

>
>> The web page displayed a diagram that indicates that they use an
in-tank
>> fuel pump.  An in-tank pump is used to pressurise the propane to well
>> above the vapor pressure of warm propane.  They use a return line -
just
>> the same as a gasoline injection system.  It makes a lot of sense to
pump
>> and pressurise the liquid because using the natural pressure of the
tank
>> would probablly allow bubbles to form in the line, causing the
injecters
>> to "spit".
>
>Definetly a pump intank or inline (less successful) is needed.  With the
>40-60 PSI boost over tank you will not freeze at the tip of the
injectors,
>loose that pump boost and they will instantly begin to freeze up.  In
most
>liquid systems the return line is there to allow vapour propane to
return
>to the tank under hot driveing conditions, but a major reason for it is
to
>allow the purging of the vapour form the lines when trying to hot start
the
>vehicle, if you have an oriface sized for liquid you will never get the
>engine started on vapour.
>
>> They had a computer that modifies the output of the standard ECM so
that
>> it will work properly with Propane.  I have a Holley Pro-Jection
system,
>> which can be programmed any way I want.  All I will need for the
liquid
>> propane system is the tank, pump, hoses, and injecters.  I would just
>> reprogram the ECM.  The only real annoyance with this system is that I
>> would have to load the appropriate program whenever I switch fuels.
>
>An intank fuel pump system will run you much money.  If you can
reprogram
>the computer you can either have an air sensor estimate the pressure in
the
>tank to adjust the trim on your injectors.  With the return line you can
>get higher pressures in the tank due to tank fuel temp than tank air
>temp.  Thus a pressure transducer (180 bucks) could be used to adjust
the
>trim on your injectors.

Rather than adjust the trim of my injecters, I would just regulate the
pressure at the injecters.  This is what the Holley system does (and
every other system I have looked at, for that matter).

>
>> The issue of freezing injecters is the only thing that worries me -
>> especially in cold Michigan winters.  Perhaps the tips would have to
be
>> electrically heated until the engine warms up.
>> 
>> Ray Drouillard
>
>If injecting into or near the T-body I still would go vapour, its
cheaper
>to build for the home builder, and you will have a costant pressure for
>injection systems.
>
>j.
>

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