[Diy_efi] LPG injection

[Derek]

> There is a bog problem with adding methanol to gasoline.  The o2 sensors
> that are on the cars are trying to maintain a stioch mixture for gasoline.
> When you add the meth, the car is a bit lean at 14.7.  This is BAD for
> detonation suppression.  I live in California where they have introduced 10%
> meth into the gasoline and I could not get the darn thing to stop detonating
> even at low boost.  Luckily they do not add meth to the 100 octane.  That is
> all I run.

Gotta address this. Common mistake. When you use a AFR number for gasoline, like
14.7, it is just a translated lambda number, which is a general indication of
fuel leaness/richness. If you have a mixed fuel but continue to use a wideband
sensor that reads in gasoline numbers, the number you are seeing is NOT a actual
indicator of fuel/air ratio in mass anymore.

Example: On a pure methanol car, a gasoline wideband will read 14.7 when the
actual ratio with the methanol is 6.45. Why? Because 14.7 is stoich for
gasoline, 6.45 is stoich for methanol, but both are really just 1.0 lambda.

Generally you shoot for the same observed number, on any fuel. Propane,
methanol, or gasoline. Methanol can generally be run a little richer than
gasoline or propane and still pick up power, but you do NOT try to get your
gasoline wideband to read 6.45 when you use methanol.

Now, the problem with mixing methanol and gasoline is the stoich mass of
fuel/mass of air ratio changes. This is because of the different ratios. On a
90% gas/10% methanol mix:

(14.7*.9)+(6.45*.1)=13.875
14.7/13.875=1.059

You would need 5% more mass of fuel to get the same actual lambda air fuel
ratio. Which works fine, so long as you do that. You were detonating because you
were running 5% leaner than before.

> An engine will make more power on methanol than propane.......I think you
> will need to put your money where your mouth is on that one. If you meant
> that vapour phase propane produces less power than methanol I would believe
> you  I am also happy to believe that you have never come across a propane
> engine tuned to the maximum. Don't mean it hasn't been done

Allow me to quote DRW Transmission page, which has a section that explains this:

"The heating value (BTU) of a fuel is how much heat energy is released by
burning the fuel. The more heat released, the higher the potential power output
from the fuel. Now lets bring up SE. The specific energy of methanol is slightly
higher than gasoline. The SE of a fuel is obtained by dividing the fuel's
heating value by its stoichiometric air-fuel ratio. This represents the amount
of heat energy a fuel can deliver for a given amount of air drawn into the
engine. In other words, how much heat energy a given amount of fuel can deliver
when it burns in exactly as much air as necessary. SE ratio is a useful measure
to compare fuels. It represents the ratio of the SE of a sample fuel to that of
a reference fuel, usually iso-octane, which is similar to commercially available
gasoline. SE of gasoline is 2.9, methanol is 3.08."


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