Hi Damon,
Just looking at the potential energy in the fuel is only part of the story. Like you alluded to, the efficiency of using the fuel brings in a number of other factors.
In just a few minutes, it's pretty easy to find out that virtually all gasoline to propane conversion kits claim a power/efficiency reduction of only 10-15% in carbureted engines. This is probably because the propane is already in a gaseous state and some percentage of gasoline travels through almost any engine in a liquid, not vapor state. This has been known for 30 years, per my earlier post about propane coversions being 85-90% efficient compared to the same engine with gasoline. I believe that this conversion factor will be more helpful in making comparisons.
What would be even more helpful is if the manufacturer of this particular propane outboard published their measured efficiency figures. I would think that any potential customer would want to consider this when thinking about purchasing the motor.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, Damon Lane <damon.andrew.lane@...> wrote:
>
> Comparisons between energy sources need to consider cost per unit of energy
> and efficiency of conversion to useful service (light, heat, motion, etc).
>
> Propane contains 24.75 kWh per gallon
> Gasoline contains 33.41 kWh per gallon
>
> So propane, with 27.6% less energy, would cost 27.6% less if all else was
> equal and we were really just buying the energy.
>
> I don't know about the efficiency of gasoline vs propane, but would guess
> gasoline engines, being so widely used for so long, would be quite
> efficient. This needs to be known to determine which engine/fuel combo is
> more economical. It's the same comparison that can make a diesel vehicle
> cheaper to operate than gas even if diesel is more per gallon, because a
> gallon of diesel contains more energy than a gallon of gasoline and a
> diesel combustion engine is more efficient than a gasoline engine. Of
> course "how much more?" in each of those comparisons makes all the
> difference.
>
> Damon
>
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