On Sun, 04 Jan 2004 18:53:46 +0000, Stewart
wrote:

Because there's more to the internet than hits alone, Biker_Bry
wrote:


Some of you were looking at the ins and outs of Liquid Injecting Propane.
I'm a Yank, so sory my measurments are in English.


Problem solved - just for trucks and not for cars.
http://www.cumminswestport.com/products/blpgplus.php
The only other firm I know of with this capability is Viallie.

The difficulties to overcome LPEFI are as follows...
1. Propane cannot hold a liquid state at underhood temps (207deg F)

= about 97 deg C. Actually, I doubt thet it gets that hot under the
hood, though there may be hot spots where the local surface
temperature reaches that. The cooling system on my car operates at
around 80 deg C (which doesn't appear to leave much margin).

Oil temp? 120 deg C?
Cylinder head Metal temp 150+ deg C?
Exhaust manifold temp? 400+ deg C?

After switch off the temps of many parts go way above 100 deg C. The
fuel rail and injector components are attached to the inlet manifold
which is bolted to the head. Makes hot purge cycle critical. Not so
bad with plastic manifolds.

In a common fuel rail system, where the fuel is continually cycling
back to the tank, then the problem may be largely mitigated by a
sufficiently high flow rate.

2. Liquid must stay at the injector at all times while running (fuel pump
nessisary)

A common rail would achieve this.

3. Vehicle must complete a purge cycle before starting similar to a diesel
waiting on glow plugs.
(to rid the fuel lines of vapor).

That's also why the fuel pump on EFi runs for a few seconds after
switching on. It puts sufficient pressure in the fuel rail to squash
the bubbles of petrol vapor back into liquid.

Not sure about a pre-starting purge, but it occurs to me that the fuel
would need to keep cycling for a while after switch-off if the
under-bonnet heat is a problem.

Excess pressure in hot fuel rail vents back to tank though regulator.
Tank should be cool enough to recondense a few mg of propane vapour
with very little temperature rise. Not going to have the same coke
and varnish problem with LPG as you do with petrol.

4. Fuel Pump must be inside the tank, so how do you pass wires through a
fuel tank and have it safe?

Same way they do it for an in tank petrol pump, only the seal has to
withstand LPG tank pressure. LPG pumps are currently in use on trucks
in USA - Cummins Westport. Temperatures drop so low that tank
pressure has to be boosted to allow injection of liquid propane at
40psi. Also available in Italy not so much for pressure but to
maintain flow rate though pipe run.

I've often wondered about getting wires into the tank in order to make
an effective fuel guage sender a possibility. But in fact I don't
really think it would be an insurmountable problem. Probably quite
easy, in fact - a solid connector embedded in enough vitreous sealant
that passes through the multivalve.

But why must the pump be in the tank, anyway? To prevent cavitation?

Yes.

BTW
Mixing air/fuel *before* the cylinder breeds backfires and they will cause
serious problems.
Ask anyone tha has used an old Impco system.

Do you mean specifically in the case of *liquid* fuel injection? Why
would this be? ATM all LPG systems mix the fuel and air before the
cylinder.

He's taking about the old mixer valve systems - noted for ability to
backfire even in UK. Never to be used with plastic manifolds. Near
valve injection of propane vapour / LPG / liquid petrol does not incur
the same risk. The real loonies use an external vaporiser for petrol
- it gives better fuel consumption as there no need for a rich mixture
when starting and cold running. It goes bang big time.

LPi (Liquid Propane Injection) is available as a factory fit item. It
is unlikely to ever be available as a retro fit item. It is a key
technology that will put a supplier of LPG systems on to car makers
1st tier supply list. As a 1st tier supplier there is little point in
dealing with 100's of small troublesome customers with lots of one
offs. Firms that don't have it will have to run after the retrofit
market which as OEM systems become the norm will see a much reduced
market share like rust proofing firms of the late 70's (anyone seen a
Ziebart installer?).

LPG diesels are available using about 5% injected diesel as an
initiator. The LPG is fed in as vapor and won't burn until the timed
diesel injection takes place. A new development is a catalytic
coating to the cylinder head to start combustion in a CI 100% propane
injection engine.

--
Peter Hill
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