"Stewart Hargrave" wrote in message
...
Because there's more to the internet than hits alone, Peter Hill
wrote:

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

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


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?

None of these present much of a design challenge. Don't bolt the fuel
rail to the exhaust manifold, and make sure it's not submerged in oil.
Most designers could manage that.

The only part that the fuel system needs to be in contact with is the
inlet manifold. I've never stuck a thermometer onto my inlet manifold,
but I doubt it gets near the critical temperature - it is constantly
cooled by between several hundred and several thousand litres of cold
air a minute. And in fact the reported issue at this point of contact
is injector freezing.

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.

It really wouldn't take much to insulate the fuel system from all
parts likely to get hot. Some cars already keep the cooling system
active for a while after switch off. The only thing left is ambient
air temperature. And it has never seemed to me that opening the bonnet
is a similar thermal experience to taking the lid off a boiled kettle.
Of course this may be different in hot climates.



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.

Why 'even in the UK'?

I would contend that mixer conversions were still amoungst the most
common type done. It is not the fuel/air mix that causes the backfire,
but a weakness elsewhere, typically with the ignition system. But I'd
be interested to learn of additional factors that liquid injection
brings up.


LPi (Liquid Propane Injection) is available as a factory fit item.

It is? So all these problems are already overcome, then.


We await your prototype

On or around Mon, 05 Jan 2004 23:35:36 GMT, (QrizB)
enlightened us thusly:


... and 300 bar isn't an unreasonable pressure for an injection
system. Many modern diesels run at roughly ten times this pressure.

you sure? the figure quoted for the later TDi Land Rover engine is 300 bar.

3000 bar is a lot.
--
Austin Shackles. www.ddol-las.fsnet.co.uk my opinions are just that
"Quos deus vult perdere, prius dementat" Euripedes, quoted in
Boswell's "Johnson".

On Tue, 06 Jan 2004 12:37:27 +0000, Austin Shackles
wrote:

On or around Mon, 05 Jan 2004 23:35:36 GMT, (QrizB)
enlightened us thusly:


... and 300 bar isn't an unreasonable pressure for an injection
system. Many modern diesels run at roughly ten times this pressure.

you sure? the figure quoted for the later TDi Land Rover engine is 300 bar.

3000 bar is a lot.

GDI goes up to about 1000psi (50bar/750psi typical) and they don't
mess around with large excess flows to allow cooling. Pump is sized
so one pump stroke delivers just enough fuel for one injection at max
power at max power rpm. They are usually driven off the camshaft but
some new ones are electric.

One problem is lubrication. Propane and Petrol will seize a high
pressure pump in no time (put petrol in a diesel tank and you can get
away with a mile across town to have the tank pumped out but won't get
a very far down a motorway). Diesel has good lube properties and some
additives.

--
Peter Hill
Spamtrap reply domain as per NNTP-Posting-Host in header
Can of worms - what every fisherman wants.
Can of worms - what every PC owner gets!

On Tue, 06 Jan 2004 12:37:27 +0000, Austin Shackles
wrote:

On or around Mon, 05 Jan 2004 23:35:36 GMT, (QrizB)
enlightened us thusly:


... and 300 bar isn't an unreasonable pressure for an injection
system. Many modern diesels run at roughly ten times this pressure.

you sure? the figure quoted for the later TDi Land Rover engine is 300 bar.

3000 bar is a lot.

Well, Bosch quote 2000 bar, which is "roughly" ten times 300 bar :-)
http://www.boschautoparts.co.uk/pcDies1.asp?c=2&d=1
http://archives.tcm.ie/sligoweekende.../story6127.asp
As do Delphi:
http://www.delphi.com/pdf/e/eui.pdf

And 2200 bar is in the pipeline:
http://www.eworldresources.co.uk/lan...n/000002fd.htm

--
QrizB

I sound like I know what I'm talking about, but don't
be fooled.

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

As the UK infrastructure is in place now is the time to
move to 100% LPG fueled vehicles with OEM optimised engines and do
away with the dual fuel conversions.

Well I'm not going to hold me breath.

Once we start to get engines designed around the fuel, then it seems
liquid injection looses much of it's point, with not much, if any,
advantage over simpler gaseous injection.



--

Stewart Hargrave

Finally visible on www.hargrave.me.uk

I run on beans - laser beans


For email, replace 'SpamOnlyToHere' with my name

On Tue, 06 Jan 2004 21:39:11 +0000, Stewart
wrote:

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

As the UK infrastructure is in place now is the time to
move to 100% LPG fueled vehicles with OEM optimised engines and do
away with the dual fuel conversions.

Well I'm not going to hold me breath.

Once we start to get engines designed around the fuel, then it seems
liquid injection looses much of it's point, with not much, if any,
advantage over simpler gaseous injection.

Without liquid injection the compression can't be raised to take
advantage of the octane rating.

A change of compression ratio from 9.3:1 to 12:1 increases efficiency
by 12% (it also gives more power). Each increase in octane by 6 will
allow an increase of 1 in compression ratio. Petrol is 95 octane,
Propane is 111, this should allow the engine to run 12:1. BUT only if
the inlet temp stays the same. If inlet temp goes up you can't
achieve the same gain and an inlet temp rise (by feeding it hot vapor)
completely negates the possibility of any gains.

A normal petrol engine has it's inlet temp reduced by about 20 deg C
due to vaporisation of the fuel. Every 4 deg C lower inlet temp
results in 1% efficiency gain (hot vapour feed results in 5% loss!).
With liquid propane this reduction in inlet temperature will be closer
to 30 deg C (2.5% efficiency gain) as the LPG will vaporise completely
unlike petrol which goes in as an atomized mist and some vapor. This
reduced inlet temp will allow a further slight increase in compression
= a bit more efficiency.

Liquid propane injection should allow an increase of about 15% on
existing engine inefficiencies. So an engine that today runs at 33%
on petrol should give close to 38% efficiency when optimized for
liquid propane. This ignores the improved combustion efficiency due
to complete vaporisation - could give over 40%! A gain of just 9% to
36% would still make it worthwhile.

A hot propane vapor injected engine looses about 5%, it regains some
due to better combustion efficiency but at best can only just match
the petrol engine.

Propane burns cooler than petrol (1925 vis 2030 deg C) but propane
vapor engines run hotter due to loss of cylinder head and valve
cooling (as demonstrated by some engines valve seat problems). Liquid
injection gives higher efficiency = more power, better fuel
consumption, lower engine temps, longer life ..... but it costs more
and can't be designed and fitted by plumbers so the cheap option wins.

--
Peter Hill
Spamtrap reply domain as per NNTP-Posting-Host in header
Can of worms - what every fisherman wants.
Can of worms - what every PC owner gets!

On or around Wed, 07 Jan 2004 21:57:17 +0000, Peter Hill
enlightened us thusly:

Propane burns cooler than petrol (1925 vis 2030 deg C) but propane
vapor engines run hotter due to loss of cylinder head and valve
cooling (as demonstrated by some engines valve seat problems). Liquid
injection gives higher efficiency = more power, better fuel
consumption, lower engine temps, longer life ..... but it costs more
and can't be designed and fitted by plumbers so the cheap option wins.

yeah, all true, I don't doubt.

But, to do this lot, you need an engine made for the purpose. Any of the
manufacturers could do this, if there was thought to be enough market -
developing or adapting an existing injection system would be simple enough,
making a high-compression engine easy enough, if someone wanted to guarantee
a market for a couple of million of them I'm sure Ford et al would jump at
it.

none of that helps convert the millions of existing engines though, which
are stuck mostly with the design built into 'em, carburetters, low
compression etc., so a retro-fit liquid-injection system is relatively
unlikely - costs too much to be practical, I expect, bearing in mind that
you're talking about a whole new fuel system, near enough, even on a petrol
injection car.

Obviously you can go some way towards it, you can pick a high-compression
engine (my ford is 9.2:1, the latest V8 I have is 9.35:1, some of the more
modern car engines are not far short of the 12:1 you quote). But that as
you say is only part of the story. I doubt any conversion supplier can fund
the development of liquid-phase injection to the point where it can be
supplied as a kit to retro-fit e.g. my V8, and if it were, it'd doubtless be
expensive, and require a fair amount of engineering to fit, so not many
people would buy it.


--
Austin Shackles. www.ddol-las.fsnet.co.uk my opinions are just that
Beyond the horizon of the place we lived when we were young / In a world
of magnets and miracles / Our thoughts strayed constantly and without
boundary / The ringing of the Division bell had begun. Pink Floyd (1994)

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

Without liquid injection the compression can't be raised to take
advantage of the octane rating.

OK, I'll bite. Yes it can. You seem to be thinking only in terms of
induction density. What's wrong with changing the dimensions of the
combustion chamber?

A change of compression ratio from 9.3:1 to 12:1 increases efficiency
by 12%

12% of what? Do you mean that an engine will start returning in the
region of 35-40% overall efficiency, or do you mean the gain will be
12% of about 25% or so, giving something like 28%?

(it also gives more power). Each increase in octane by 6 will
allow an increase of 1 in compression ratio. Petrol is 95 octane,
Propane is 111, this should allow the engine to run 12:1. BUT only if
the inlet temp stays the same. If inlet temp goes up you can't
achieve the same gain and an inlet temp rise (by feeding it hot vapor)
completely negates the possibility of any gains.

I'm not convinced that your interpretation of figures accounts for all
considerations.

The effect you describe of cooling the charge, making it denser, has a
similar result to supercharging - both are ways of enabling more
charge mass to be packed into the combustion chamber during induction.

But there is another way, too. Increase the stroke. Although
volumetric efficiency will not be comparable, both can achieve much
the same thermal efficiency, which is, in the main, a function of how
much the charge, once inducted, gets squeezed.

The comparisons you give may be right for the same induction
temperature, but that is not the same as saying that induction
temperature has to be the same. We need to consider the nett result of
a specific mass of mixture compressed to a specific volume. My
understanding is that in a) a cooled, dense charge going into a
compression chamber (liquid injection), or b) an ambient, less dense
charge going into a higher compresion chamber (vapour injection),
thermal efficiency would be the same. But the relative power/torque
curves of mechanical output would not necessarily be so, and the
engines may have different characteristics.

A normal petrol engine has it's inlet temp reduced by about 20 deg C
due to vaporisation of the fuel.

In theory, (or so my back-of-envelope clacs. show) LPG that becomes
vaporous in the inlet manifold could reduce the charge temperature by
more than this. In reality, other factors would probably prevent it
from either achieving or sustaining this.

As well as improving volumetric efficiency, this temperature drop
would translate into some cylinder cooling resulting in lower
pre-combustion temperatures. But probably not as much as you may think
- there is a lot of heat capacity in the elements around the cylinder
compared to the relatively trivial capacity of the inducted charge. A
lower charge temperature could mean slightly higher compression
pressures could be run and thus better thermal efficiency. At the
moment I've run out of envelopes, but I'd be surprised if in practice,
lowering the temperature of the charge by a few degrees on a working
engine enabled much of an increase in TE.

Every 4 deg C lower inlet temp
results in 1% efficiency gain (hot vapour feed results in 5% loss!).

Are you talking about volumetric efficiency or thermal efficiency
here? VE figures are lovely to bandy about at dinner parties, but
don't necessarily equate to good TE. If you do mean TE, then do you
mean 1% of 100%, or 1% of 25%? And is this on a specific engine
configuration, or does it account for variations up to the compression
limit?

[..]
to 30 deg C (2.5% efficiency gain)
[..]
allow an increase of about 15% on
[..]
an engine that today runs at 33%
[..]
should give close to 38% efficiency
[..]
could give over 40%! A gain of just 9% to
[..]
36% would still make it worthwhile.
[..]
looses about 5%, it regains some
[..]
burns cooler than petrol (1925 vis 2030 deg C)

Where does your prolific abundance of figures and statistics come
from? Just out of interest, like.




--

Stewart Hargrave

Finally visible on www.hargrave.me.uk

I run on beans - laser beans


For email, replace 'SpamOnlyToHere' with my name

On Fri, 09 Jan 2004 02:37:50 +0000, Stewart
wrote:


Where does your prolific abundance of figures and statistics come
from? Just out of interest, like.

The internet seems to work quite well - yields stuff like FAQ on
gasoline, turbo charger tuning sites, LPG sites, chemical properties,
NACA research papers.

--
Peter Hill
Spamtrap reply domain as per NNTP-Posting-Host in header
Can of worms - what every fisherman wants.
Can of worms - what every PC owner gets!

SimonJ wrote
Damn, and there was me thinking we used Centigrade TIC

And I thought it was celcius!

The official SI name is "Celsius". See the SI website:
http://www1.bipm.org/en/si/derived_units/2-2-2.html