Propane Motor Fuel Injection

[Jonathan R. Lusky]

dn writes:
> 
> Before you dismiss me as a crank, let me tell you about the advantages of 
> propane as a motor fuel:
> 
> 1. cheap - at least here in Canada, less than half the cost of gasoline

per gallon yes, per mile, not quite.  I don't remember the exact number,
but the energy content of propane is significantly lower than gasoline.

> 2. high octane rating - upwards of 125 combined octane rating - this allows
>    high compression engines with all their advantages.

I think you are getting propane confused with CNG here.  Propane is down
around 110 octane.

> 3. engine wear - since propane is a gaseous fuel, there is no washing down
>    of the cylinder walls as with gasoline, so cylinder and ring wear is
>    drastically reduced.

No argument here...

> 4. clean - both from an emissions standpoint and from engine internals, there
>    is much less carbon buildup with propane.

With respect to emissions, not really.  Gasoline 3-way catalysts don't
work particularly well with propane, so you generally end up with worse
emissions overall than a modern FI 3-way cat equipped vehicle.

> 5. fuel mixture - again since propane is a gas, there are no problems with
>    improper fuel distribution and fuel puddling in the manifold, nor 
>    problems with fuel vaporization at low temperatures.

Well, thats true about vaporization in the intake, but fuel distribution
with gaseuos fuels is actually more of a problem that with liquid fuels.
You can end up with pockets of unmixed fuel/air in your combustion
chamber.

> 6. simple - since the fuel is already under pressure, the system needs no fuel
>    pump.  Also, the carburetors are extremely simple devices. 
 
But for the most part the technology is really crude, and hasn't
advanced much in the past 20 years.  On, the other hand, if you know
what you are doing, you can get really spectacular mixture control
(open loop no less) out of some of those mixers...  with an OHG X450
(think that was the model #), i was able to get my fuel mixture
absolutely perfect across the board, and even got it to do deceleration
enleanment!  (spent a good bit of time machining the fuel valves).

> The system itself would be remarkably similar to a gasoline EFI system, but
> one as-yet insurmountable problem I have encountered is the fuel injector 
> itself.  Firstly, it needs to be able to handle a fuel pressure of about 150
> PSI. The other problem stems from the amount of fuel needed. Propane expands 
> something like 270 times from it's liquid state to it's gaseous state, so the
> injector would have to be accurate with very small volumes of liquid fuel in
> order to meter the correct amount for a given air fuel ratio, especially at 
> idle.  Unfortuneatly you can't simply regulate the fuel pressure down to a
> more manageable pressure, at least not by any means I am aware of, since
> there is nowhere for the unused fuel to go.

I believe BKM makes injectors (designed for CNG) that will handle 150psi
with no problems.  They may be too for what you want to do, though.
Keep digging around, because i know there is someone out there selling
EFI kits for propane.  You might see if Stewart-Stevenson has one...
they were one of the first people to come out with a complete TBI kit
for CNG.

> I haven't dyno tested it.  I think I could improve on this greatly, however
> with some decent fuel metering and a modified ignition system.  I plan on
> using an HC11 as an ECM core, firstly doing a timing control system, and
> gradually adding the EFI to it.  If anybody out there has any ideas on how
> to solve the injector problem, LET ME KNOW!!!.  

EFI would definately be cool, but I think you could get nearly the same
results with an OHG mixer (what are you running now, Impco?).  But for
ignition, computer control based on RPM, MAP, and coolant temp is the
ONLY way to go :).

-- 
Jonathan R. Lusky                        lusky at knuth.mtsu.edu
http://www.edge.net/~lusky/                 (615) 726-8700
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68 Camaro Convertible - 350 / TH350  \_/ 80 Toyota Celica - 20R / 5spd