Take a look at my post about my experience with propane in this forum under the topic ...

let's try this alcohol thing again

Post Name : BlueFace

Right now (March 30 2005), here in Canada, it is more expensive to run a vehicle on propane than gasoline.

As far as power is concerned, with propane, if you are pulling a heavy load you will notice there isn't as much power as with gasoline. Without a load, there is no noticable power difference. Although the power difference is not noticable, the engine consumes more fuel ... which means propane gets worse gas mileage than gasoline in order to maintain power. So, if propane is 70 cents (USD) a gallon it will cost you (in my guess) about 20 per cent more in 'gallons' to drive 100 miles, thus, the effect is you will be paying 84 cents a gallon for propane. Again I need to say the 20 percent number is a guess on my part but, the important thing here for me is to help you undetstand you will burn more gallons of propane to go the same distance with gasoline.

I considered using natural gas as a fuel. Here is the big difference between it and propane. When a propane tank is filled to its maximum allowable limit, the pressure in the tank is around 100 psi (there is a built in safety valve that blows at about 300 psi). With natural gas, the pressure is 2400 psi (if I remember correctly), with gasoline the pressure is zero. With propane and natural gas, if the tank is ruptured in an accident, fuel is instantly sprayed and likely ignited. If the fuel line is cut, the fuel sprays out and there is no way to stop it. With gasoline, it may drip out of the line and stop, or you can turn the key off to stop the fuel pump from pumping ... with propane and natural gas the entire contents of the tanks will be emptied everytime. In short, you will have to literally run for your life.

When a propane tank is filled, the propane is in liquid form as it sits in the propane tank. When a natural gas tank is full the nautral gas is still a gas ... it doesn't become liquid under pressure like propane does. This means that 1 cubic foot of liquid propane has far more power in it (because it is liquid) than 1 cubic foot of natural gas (because it is a gas). What this means, is, you need a MUCH larger natural gas tank to go the same distance as propane and gasoline. As I remember, the range for my van on natural gas would have been something like 100 miles. Buses are big vehicles and thus have the room to handle larger tanks, that's why (I think) they can use natural gas more effectively.

Because natural gas is stored at 2400 psi it means it takes a lot longer to fill the tank. The fuller the tank gets, the higher the pressure and the harder it is for the pump to force the gas into the tank. If there are 3 vehicles in front of you at the filling station count on 30 to 45 mins before your tank is full.

With natural gas, if you run out of gas, no one can bring you a 'gas can' of 2400 psi fuel ... this means you will have to be towed to the nearest gas station.

With natural gas, I don't think there is a "gas gauge" per se ... it is a pressure gauge ... so you have to know that 973 psi means 34 miles to go (or whatever). Propane is in liquid form in the tank and the gas guage actually measures the number of gallons in the tank.

Because natural gas is stored at such high pressure, it means the fuel tank must be thicker thus heavier than a propane tank. The extra weight may be a consideration for you.

For propane to turn into a gas it needs heat. At -40f propane will not turn into a gas ... and your vehicle will not start ... period. With natural gas, the 'magic' temperature is something like -450f ... so natural gas has the edgde (smile).

A buddy of mine had a propane vehicle. He said he used to be a mechanic (right), and as he started to 'adjust' the air\fuel on the vaporiser (carburator) I told him not to mess with it because he will burn out his valves. Of course 6 weeks later I asked him what the ticking noise was in his engine, and he said GM has a problem with their valves cupping, and sold the vehicle. I think he screwed it up by playing with the mixture.

With propane, if you adjust the air\fuel mixture, and lean it out, the leaner it burns, the hotter the flame temperature in the cylinder ... the quicker you burn out the valves. BUT there is absolutely no difference in engine performance as you lean it out ... it has the same power as a rich mixture ... thus you cannot tell by listening to the engine if the mixture is too lean or too rich ... this means you need a CO2 detector to measure the exhaust to set the mixture properly ... and once it is set ... DON'T CHANGE IT. (see my buddy's story above).

Lean propane burns at a MUCH higher temperature than lean gasoline does, and thus propane can burn valves much easier. I know that todays valves and seats are 'hardened' and resist burning but you can still burn them.

If I were to build an engine to run on propane, I'd find out how what the maximum compression rating is for the octane rating of propane (103 to 110 I think), then build to those specs for maximum compression.

Does anybody know what the maximum compression would be for an octane rating of 110?