Propane injection (was Nitrus injectors (was Hydrothermal

[Raymond C Drouillard]

On Sat, 20 Jun 1998 11:45:27 -0500 "Joe Chiasson" <chiasson at hutchtel.net>
writes:
>> 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.
>
>I agree you will cool the intake charge somewhat, however the farther
away
>from the cylinders you are the less effective it will be.  I don't know
>exactly how less effective it will be.  Injecting liquid into the
cylinder
>or near should gain 8-10% more power than gasoline lb per lb.  What is
the
>power gain by injecting liquid into T-body, i don't know.

Considering how much frost is generated around a propane leak, I would
imagine that the intake charge will be cooled considerablly.  Injecting
the propane upstream will allow the propane to completely vaporize, and
therefore extract as much heat as possible from the air.  (As I said
before) you want to keep gasoline in a liquid state until it enters the
cylinder because the gasoline vapor will just take up space.  Propane,
however, will absorb heat  as its evaporating, and thus cool the charge. 
We therefore want it ALL to evaporate.  That is, IF the cooling effect is
enough to make up for the volume of the added propane.


>What formulas and properties do you still need to perform your
calculation?

I found a list of the properties of Propane on the web (unfortunately,
it's at work right now).  I still need a list of the vapor pressure at
various temperatures so that I'll know how much the vapor pressure
changes with the temperature, and how much pressure I'll need to keep all
of the propane in a liquid state in the tubing that will be in the hot
engine compartment.

I need to know the specific heat capacity of air and propane (gaseous
state).

For ideal gases: P1 * V1 / T1 = P2 * V2 / T2

Assuming you know the variables on the left side of the equation, and
compress the gas to a specific volume, the gas will be hotter (T2) and at
a higher pressure (V2).

V2 / T2 = (P1 * V1) / (T1 * V2)

I want to be able to calculate T2 or V2 (If I have one, I can calculate
the other).  This assumes that no heat is exchanged.

I'll fiddle with the equations to figure out how much denser the cooled
air will be.

  In any event
>if its less than 2-3% gain it may not be worth trying to inject liquid
>(i.e. just the imense cost to have a pump in a pressure vessel, wether
it
>is in the tank or inline, protoyping a one-off could put somebody in the
>poor house.)

That's part of what I want to determine.  I need some injecters that'll
handle about 200PSI, and a pumnp that'll increase the pressure to 200
PSI.  A standard in-tank fuel pump might do the trick, since it'll just
be increasing the pressure from 150 PSI up to about 200 PSI - an increase
of only 50 PSI.  The only trick will be to either seal or pressurize the
motor so that it'll operate at an ambient pressure of 150 PSI.

> 
>> Rather than adjust the trim of my injecters, I would just regulate the
>> pressure at the injecters. 
> 
>Thats fine.  When you take a pressure drop in liquid propane (i.e.
regulate
>it) you are going to form vapour bubbles.  If you size your injectors
for
>liquid and vapour bubbles from the regualtion process enter the injector
>you will vapour lock.  Keep this in mind when you design your regulator
and
>return system.

The purpose of the fuel pump is to get the pressure above the vapor
pressure of the propane.  I plan on keeping the pressure constant, not
varying it to control the fuel.  The standard method is to let the pump
run wide open and restrict the fuel goinng to the return line.  That way,
the pressure at the input of the injecters is kept at a constant value. 
I plan on running the system at arount 200 PSI, but I need to see a table
of the vapor pressure of propane at various temperatures before I make a
final decision.

>
>> This is what the Holley system does (and
>> every other system I have looked at, for that matter).
>
>I don't know much about the Holley system, but are you telling me that
>nobody adjusts the trims on their injectors and its all done by
regulating
>pressure at the fuel rail or injector?  
>
>Regardless of that, if you have a liquid propane system, and have the
>ability to fully modify your fueling curves, then triming the curves
>relative to either a fuel temp sensor or a pressure tranducer will make
it
>a lot easier than trying to regulate.  I am not saying that regulating
is
>impossible,  i am not saying don't inject liquid at the t-body, i have 4
>years experience (not much but more than many people) with propane
systems
>and am just trying to relay some of the pitfalls I have encountered or
>witnessed.
>
>j.
>
>
>
>
>
>

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