All the non-DYI-EFI crap I've put up here

[Joe Chiasson]

Bi-fuel dual fuel, I'm always getting those mixed up, don't think I will
ever get it right.
Anyway thanyou for your reply, it sounds like a very interesting system, I
really hope it works.  I have been considering more of a dual fuel system
myself (gasoline and propane with propane being the primary and gasoline
being a back-up, main reason some places its hard to find establishments
which are licensed to fill motor vehicles.) Your bi-fuel system, as I said,
seems really interesting, perhaps out of my ball park (not a wiz with
controllers yet), but reading about your system may push me to go ahead and
work on a dual fuel system.

However, I hope that you do not mind some commentary.  Withdrawing vapour
off the top of the tank could hinder your system in two possible ways.  One
location of the tank is usually in a cool area when compared to the engine
compartment.  If you end up having to drive off the vapour injectors for
any extended period liquid propane will have to keep vapourizing to replace
the vapourous propane removed form the top of the tank.  This takes large
quantities of heat, which usually get extracted from the tank system
itself, cooling the tank temperature, reducing the pressure, with reduced
pressure less vapour will flow, thus you will starve your engine (all
depending on what pressure you were planning to inject with in the first
place).  Senario 80 F day, where tank temp was essentially 80 F.  15
gallons of fuel drained from a 51 (80%) gallon tank through a vapour port
at the top of the tank.  When all was said and done the finall tank
temperature was 4 F.  Now you are still 48 degress above freezing point of
propane but the vapour pressure is seriously reduced.  Just above 26 psig. 
But with a good lean burn system you would probably be regulating down to
this pressure anyway (maybe  less 17 psig).  This leads me to the second
problem,  cold starting and cold driveability. -25 F vapour pressure is
about 8 psig, not enough fuel getting to your engine.  My suggestion would
be to withdraw from the bottom for the vapour system and vapourize it under
the hood where there is plenty of heat.  But if you are only going to drive
it in the warmer weather, and withdraw vaopour for small periods of time,
then you shouldn't have to worry about the above.  As for a dry gas
regulator I have not heard of an automotive grade one, but there are
laboratory grade regs, and for all intesive purposes you should be able to
build one your self.

Its seems that you are going to have a good controll strategy which should
handle most engine fueling demands, however, if you are planning to have a
predictable amount of liquid propane you may have to enlist the services of
an in-tank pump (as in the chrysler liquid injection system) or an external
pump (tuthill???). Also, I don't know if you mentioned it, the liquid
system should have some way of returning the vapour, generated in it, to
the tank (return line to tank or perhaps a line to your vapour injectors).
Reason unless you can pump the liquid up to an enormously high pressure, or
completely isolate the lines from under hood heat, the liquid will flash to
vapour in your supply line.  This can cause a vapour lock in your system.
Main reason why the chrysler system uses bottom feed injectors. The oriface
used to pass the liquid into the system is probably going to be smaller
than the vapour injectors (liquid unregulated pressure > regulated vapour).
 Thus your controller will call for x lbs of liquid propane and only get 
.1x lbs of vaopour propane, or something to that effect.  If you have a
return line back to your tank you can continously pump fuel into your
liquid distribution system cooling it, purging out any vapour (which would
really accumulate under hot soak condintions) and thus get liquid when you
want it.

My apologies for being long winded.  Again good luck with this system. Its
looks very attainable with easy to aquire hardware and one seriously crazy
control stratgey. Keep us posted of you progress we all could learn a lot
here.

J.  
----------
> From: Robert Harris <bob at bobthecomputerguy.com>
> To: diy_efi at coulomb.eng.ohio-state.edu
> Subject: Re: All the non-DYI-EFI crap I've put up here
> Date: Saturday, September 13, 1997 11:34 AM
> 
> What I would like to do and am working out is correctly called a Bi-Fuel
system
> (i.e. using two fuels at the same time) rather than a Dual Fuel (using
either
> or system).
> 
> Fuel A  Timed port injection Vapor Propane.  A poster ran Methane on a 75
lb
> per hour Alcohol Injector at 80 psi and got 19 lbs per hour.  Another
mentioned
> Big Block Chevy Injectors run 75 lbs per hour and handle reasonable
pressure. 
> Using a dry vapor regulator off the top of the tank (still looking - any
clues)
> will plumb the regulated vapor to the injectors.  Looking for 15 to 20
lbs per
> hour. Getting info on any number of TPI EFI systems that can be used. 
Start,
> run, idle, low - mid range on Propane Vapor.
> 
> Fuel A prime.  Liquid Propane.  Think NOS spray bar or direct port.  Will
run
> line from bottom (liquid) line unregulated to NOS type Gas Solenoid at
spray
> bar. Sense RPM, throttle position and PW of injector (and other depending
on
> final EFI selection) to determine turnon.  Measure Tank Pressure and
apply
> curve for volume thru orifice correction.  Grossly adjust EFI - finely
regulate
> thru Oxygen.
> EFI selected must run closed loop at WOT as with propane, richening past
stoich
> RAISES temp's to meltdown range - not runs cooler.  Got to error on lean
side. 
> Each spray bar step will be power of two flowed so step two flows twice
of step
> one and strep three flows twice of step two.  This gives me 8 points with
the
> step
> approximately equal between the points.  May only wind up with 2 as this
covers
> a wide range with reasonable cost.
> 
> What I get at this point is an off the shelf injection system that is
tweakable
> by a Chris Johnson or other chip or programming package to be just happy
fine
> on Propane.  All the controllability of TPI with SIMPLE CIS for taking
> advantage of the high latent heat of evaporation.
> 
> Fuel B will be unleaded pump gas to use as a cheap extender fuel. 
Gasoline is
> cheaper than propane in most parts of the country and as this system is
going
> on an RV, would like to take advantage of it.  Also, if you can avoid
start,
> idle, and very light load, you avoid most of the problems.  Plan is after
> warm-up, and under cruise load, to switch the vapor injectors out and use
> gasoline thru small injectors located near the port.  This will be an
either/or
> situation - not both. Sizing the propane and gasoline injectors flow
similarly
> and using the gasoline primarily to trim or light moderate load portion.
May
> delay liquid propane steps till later in the pulse width to allow more
> gasoline. A hidden side benefit of gasoline this way is to extend engine
life
> even further.   The major wear point on a LPG/CNG engine is the uncooled
and
> unlubricated exhaust valve. Gasoline contains lubricants for the exhaust
valve
> and adding Instead of Lead would really eliminate the wear.  Could
probably get
> away with not using unobtainium exotic valves and seats.
> 
> I can now have a high torque, hi compression (efficiency goes up
startlingly
> with compressions over 9 to 1), very clean burning, very long life engine
that
> can pull heavy loads without detonating.  Gasoline has 20 percent more
energy
> per gallon (but less per pound) than Propane and using it in a propane
> optimized engine gives even greater economy.  Since the fuel switches to
higher
> octane, much colder liquid propane under load, I can forget about
gasoline
> detonation limits on a high compression engine.  Also note that gasoline
is a
> major player only under light moderate cruise loads where the extra
propane
> advance and higher compression really kick in.  If I experience light
ping, can
> run a solenoid valve from the regulated vapor to a central intake point. 
Set
> the hole size to supply most of the fuel for idle.  Now will have a 112
octane
> "trickle" that should kill the light ping dead like DI.
> 
> Fuel selection is Propane, or Both.  Limp home on gasoline risks the
China
> Syndrome or interstellar beginnings on a high compression big block.
> 
> As cost IS an object and Keep It Simple Stupid rules apply - I think I'm
> nearing the point when I can get it done.  Please note - if both
injectors flow
> the same amount of fuel in Pounds per hour, the EFI should be well within
trim
> range for either fuel.  Also, by limiting the range of control for the
timed
> injectors, I keep the cost way down without sacrificing any performance
or
> economy.
> 
> Also looking for moderate priced wide range O2 sensor as propane Likes to
run
> lean - up to about 18 to one and runs COOLER leaner.  Thiminking about
how to
> do this.
> 
> Usual disclaimer - just my normal wild ass guessing and dreaming
> 
> "When some one gets something for nothing -
>              some one else gets nothing for something "
> 
> If the first ingredient ain't Habanero, then the rest don't matter.
> Robert Harris <bob at bobthecomputerguy.com>
> 
>