I own a small fleet of trucks with 454's. I am considering converting them to run on propane. Now, I know propane has less BTU's per gallon than gasoline. How much more propane is needed to go the same distance as gas? Right now, for example, gas here is about $2.10/gallon and propane is still at $1.85. Is it still cheaper to run propane?

density of liquid propane is .54 kg/litre

calorific value is 46.3 MJ/kg

gas is .74 and 42.7 respectively.

You'd be losing money hand over fist. Propane has to fall below 80% of the price of gas, per gallon, to break even.

Cheers

Greg Locock

I believe you can get propane cheaper by buying a large storage tank, and buying it from a distributor. I just picked up the phone and found it $0.20 cheaper than at the gas stations.

Now if you were to have engines optimized for propane (12:1 compression), you would gain quite a bit of mileage/BTU, and power, which would make it worth it for sure.

In Texas vehicles that run propane pay an annual fee of about $200 and then they do  not have to pay any taxes on the propane, so they price per gallon on propane becomes very competative.  Engines running on propane will last much longer and your oil will be changed much less.

Dcasto;
In Texas, you will pay an annual State road use tax based on vehicle weight and estimated miles driven.  For a 4000 lb vehicle at 10,000 miles, you will pay the about $85 USD, then a Federal imposed price per gallon of 13.5 cents.
http://www.window.state.tx.us/taxinfo/fuels/lg.html
Then at 162.305:
http://www.capitol.state.tx.us/statutes/docs/TX/content/htm/tx.002.00.000162.00.htm

With the prices of gasoline soaring, LPG is competitive, pity there arent many autos taking advantage of it.  The EPA has strict guidelines on vehicle conversions, tailpipe emissions, and the general public demands bullet proof conversion systems, something which the OEM's tried then finally gave up on.  There are a very few GOOD aftermarket systems that perform well, and these are NOT the old bolt on yourself systems.  Conversions now cost around $6500 USD, which buys an EPA compliant system, multiport fuel injected and OBD II compatible.

Franz

Anybody mention the valve wear/valve seat recession issue with propane?

You'll have to save a huge amount on fuel to pay for the valve jobs, IMO.

The valve and seat wear issue with propane is the same as with any unleaded fuel. If you have the correct seats and valves for unleaded, or if you run leaded fuel ocasionally, or if you use the correct additive as lubricant, you will have no problems

Regards
pat   pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

In regards to valve seat recession, Pat is essentially correct.  Since the use of unleaded gasoline fuel, the incidents of seat recession are few and far between.  Remember the properties of propane, it has an octane of 104, meaning that in addition to other characteristics, the fuel has a long burn duration.  If the ignition sequence is not initiated at the proper time, the combustion is still occurring when the exhaust valve opens, superheating the valve.  This can cause tuliping of the valve, and once it breaks the valve seat seal, the seat can recede.
A properly set up engine, compression, valve timing, and ignition system, will show no adverse reaction to using propane as a motorfuel.
Franz

Sorry franzh

I presumed correct tune.

I hate dual fuel conversions for that reason, and I really like the idea of going to forced induction at the same time as changing fuel, so you optimise the use of the 104 octane, and get both an economy and performance boost.

I really wonder that when car companies make Taxi specials with factory LPG, why they don't put in big tanks, one fuel only and high compression head or pistons (say 11:1) so that they can tune to optimise the result from the fuel.

Maybe they do elsewhere, but they don't here. Our LPG is an inconsistent mixture of Propane and Butane, so 11:1 is about as high as you could go with the worst brew you might get.

Regards
pat   pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.