Re: Propane Powered
Since propane has fewer BTUs per gallon than gasoline a given engine will produce less horsepower on propane than it will on gasoline. If an engine is properly set up for propane this lower BTU/gallon disadvantage can be largely offset due to the higher octane rating of the propane. At 110 octane propane allows running a higher compression ratio and advanced ignition timing. Since the higher compression generally requires a wider plug gap and stronger spark an improved ignition system is often required. The engine must be designed to handle the higher pressures of the increased compression ratio or early mechanical failure may be expected. Lack of any lubricating additives or valve seat protection dictates that hard valve seats and Stellite exhaust valves be used.
Depending on the type of fuel system the engine has, carbureted or injected, the fuel may enter the air stream as a liquid or vapor. If the liquid is injected just ahead of the intake valve it vaporizes and cools, there by condensing, the air stream entering the cylinder. This vaporization is completed after the intake valve closes which allows more oxygen to have entered the cylinder and boosts the compression pressure. The resulting HP increase is significant over the vapor fed engine.
When vapor is fed thru the intake manifold the two methods usually employed include vapor from the tank and liquid fed to a vaporizer and then regulated into the intake air stream. Using this method the vapor displaces considerable intake air and results in less oxygen being taken into the cylinder. While less expensive to produce, and somewhat easier to maintain, this method is inferior to the injection method for engine efficiency and HP output but much more common to find in use.
Vaporizers commonly used are liquid heated, from the engine cooling system, and air heated. I've seen vaporizers that used the heated air from the cooling system on air cooled engines but have also seen a couple that had a heat collection system from the exhaust manifold. Both methods were thermostatically controlled and seemed to work well.
The tank vapor systems I've seen were used on stationary engines and fed from large tanks with sufficient surface area to allow heat absorption sufficient to supply the engines needs.
Personally I like using propane as a fuel source when the engine has been properly set up for this purpose. Seldom have I seen engines that were thus set up being used on small equipment. The efficiency, and cost effectiveness, of propane on a "conversion" that has had only the fuel system changed is highly questionable.
Just my opinion on all this of course, your milage may vary.
A gun and a parachute are much the same. When you need one nothing else will really suffice.