pietenpol2002 wrote:If you've read Mr. Sharkey's teatise on propane fumigation you'll recall that a camper bottle of LP lasted him 60 miles with full-time use on his 1.6L VW. If you're engine is 1/3 the displacement of his, it would last 180 miles. When used as on-demand roughly 20% of the time, it would last 900 miles. Camper bottles can often be found on sale for about $3.00 making the cost $.03/mile. Do I have that right??
Let's calculate cost per driven distance on full power - that's more honest an indicator. Of course that bottle would last longer than 240 miles total because full power is not always needed, but exact "mileage" could vary each day drastically depending on whether one chooses/has to scoot around town or rattle down the highway...
Doesn't Alex have a 400ccm engine on his bike, BTW? So a fourth of the VW's displacement. 240 miles. A wee bit more than one cent per mile, a buck and a quarter per 100 miles, or 86 cents per 100 kilometers - on constant full propane "boost". Not bad at all considering that Mr. Sparkey calcultimates around 10% power increase.
We have, though, to yet take into account the actual supercharging (Sparkey's pusher had none), i.e. +5 hp in the case of a 400 ccm Yanclone so the goal of 75-80 MPH can be reached. With supercharging, you can squeeze out that much more power, but it will come at the cost of that much more LPG consumption to keep the diesel combustion efficient - say, if he were to boost the engine to gain yet five more additional HP (assuming he did the necessary mods such as shimming the head or delaying the injection), he'd get an additional propane cost of roughly one buck and three quarters per 100 miles at 15 hp instead of 10, and that cost is probably still underestimated. Starts getting hairy, innit? And we have not yet calculated in the cost for the additional diesel fuel.
At which point, using a proper propane tank instead of camper stove cartridges becomes imperative because it is cheaper to refill propane than to buy the cartridges, and here we run into the other problem you mention:
The risk is related to utilizing a fuel vessel that's not DOT approved. The fine is rather stiff. But since you'd naturally be painting your camper tanks to match the bike, I don't know that if stopped, the officer would even recognize it as being propane. Not that I'm promoting such practices you understand. If however you chose to engage in such practices, you'd likely want the tank well protected within the frame and not one of the first things to be creating sparks when you go down.
And that is without taking into account that propane is gaseous and spreads pretty fast in all directions, unlike a liquid that would only drop or flow downward - like alcohol, which is also harder to get to burn with sparks under atmospheric pressure than a gas.
In contrast to propane, you can store ethanol in all sorts of plastic tanks that ARE DOT/TÜV/MOT/... approved - oil tanks for self-mixing two-stroke bikes and scooters come to mind. Again, these are easier to tuck into the frame where they are safe from grinding against the tarmac should one come to fall with one's bike, and light enough to allow you to carry your fumigation fuel in sizeable quantities.
Also, I would wager there is more of a power gain to be had from alcohol fumigation than propane - because it keeps its liquid state longer and evaporates later, thus taking away less air from the combustion of diesel fuel (remember how all propane/CNG converted gassers lose some power unless the LPG/CNG is injected into the cylinder directly which costs an arm and a leg? That's because when on LPG/CNG, the engine inhales a fresh charge where the fuel is completely gaseous and takes up so much volume that would otherwise be available for the air), and also itself needs less oxygen to burn - meaning you can inject more of it to gain more power!
. Or possibly even while still riding :-\
