Propane/water/alcohol injection and O2 sensors

William Shurvinton shurvinton at orange.net
Wed Apr 10 23:39:00 GMT 2002


Not totally mixed up ( I hope), just ineloquent with the bits I am unsure
about and a few holes in my thermo theory. Badly taught thermodynamics is a
very dull subject. I should pick up my text books again and have another go.

Also bear in mind that my toy car has a Wankel engine which has some odd
requirements I still don't fully understand and seems to like slower burning
fuels. There is also little opportunity (in NA form) to raise compression to
take advantage of some of propane's burn characteristics. And this is where
the confusion often catches me. High octane fuels are often faster burning
than low octane. But also sometimes slower. A RON number isn't always useful
:-(

Petrol in UK is over $5 a gallon, Propane 1/3 that so it is well worth
thinking through. Losing 5% power due to cruddy vapouriser technology is a
high price though.

I need to think through why calorific value should force propane to be less
powerful. Surely it's related to AFR. propane has a lower stoichometric
ratio than gasoline (9:1?) so should be capable of the same power or more.
You just use more of it as the energy density is lower? But I fully agree
that benefits are mainly related to the fact that you are combusting a gas,
not a cloud of globules.

It would appear that practicalities would drive an efficient implementation
to be direct injection as you say. Thinking about it this makes a lot of
sense. This would be doable in a rotary and you would get a significant
injection time during the compression stroke. It's just injector cost that
could be a killer. I'm guessing they are not cheap.

Well worth more investigation, if only for curiousities sake. Some
interesting trade potential trade-offs.

Bill
----- Original Message -----
From: Perry Harrington <pedward at apsoft.com>
To: <diy_efi at diy-efi.org>
Sent: Wednesday, April 10, 2002 8:27 PM
Subject: Re: Propane/water/alcohol injection and O2 sensors


> I think that you all are being mixed up.  There is one fundamental that
> you cannot escape:  Propane is 95,000 BTU per gallon, Gasoline is
something
> like 114,000.
>
> Propane will always provide less thermal energy than Gasoline.
>
> Any gain in HP is entirely due to phase, temperature, and residual
efficiencies
> of atomization.
>
> Propane has less energy than Gasoline.
>
> All the commercial Propane injection I've seen puts the injector in the
intake
> elbow of the air path, shortly after the air cleaner.
>
> I had a friend with a Propane powered Caballero, he said it was less
powerful
> than when it ran on Gas.
>
> It makes sense that liquid Propane would make more power than gas, because
of
> the density of the liquid and the neccessary state change to a gas in the
combustion
> chamber.  Instead of losing all that thermal efficiency in the intake,
where it
> makes a low efficiency cooler, you get it directly inside the combustion
chamber.
>
> But cooling the intake charge extremely is counterproductive to
combustion, and so
> is the higher octane of Propane.  Unless you need the extra octane, you'll
get less power.
>
> So, to sum up:  Propane has less energy per lb than Gasoline.  It has a
higher RON
> than pump Gasoline.  Therefore it has less energy and a slower combustion
rate than
> pump Gasoline.
>
> Any advantages are NOT attributed to the cumbustible properties of
Propane.
>
> --Perry
>


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