Quote:
Originally Posted by GeorgeWiseman
Propane is typically vaporized before being fed into the airstream going into the engine.
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Some additional thoughts that may help people who already have propane fuelled engines.
First, make sure your propane is actually being vaporized. A lot of pre-heaters are insufficient to raise the temperature of the propane high enough to assure the liquid turns to vapor (flash boils) once it is metered into the airstream. If some of the propane is still liquid, it will suck the heat out of the air trying to become vapor. Less heat (enthalpy) in the air will reduce the efficiency of combustion.
You aren't likely able to do much about increasing cylinder pressures (maybe turbocharger?) or change valve timing but you can be sure that the ignition timing is optimized for propane. Some engines will allow the ignition curves to be modified. Sorry I can't be specific, my reference books are in storage 2500 miles away, but such information should be available online and from propane fuel system experts.
Be sure your propane fuel tank stays 'warm' (but no more than 90°F or it could over-pressurize). As propane is removed, the remainder of the propane cools down, as it cools down, the tank loses pressure that your fuel system may be depending on to maintain a correct air:fuel ratio. The tank usually reheats by gathering heat from the ambient air, but sometimes fuel draw can cool the tank faster than it can recover. Just something to watch for.
I've also noticed that quite a few propane powered vehicles use too much fuel, making a stinky exhaust. Properly combusted fuel has almost no smell (at least for me
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In any case, a careful study of your fuel system and how it works can often turn up a few places where efficiency upgrades can be made.