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Is propane always used in gas form or could one inject liquid propane instead of gasoline in a DISI engine. i know propane is a liquid at sub zero temperatures and vapor lock might be an issue. also is propane corrosive-both gas and liquid? i would not expect it to be as there is no oxygen in the propane molecule.
if propane is such a clean fuel why arent we using it in abundance? is the volumetric efficiency decrease so high?

RE: Propane

In Australia liquid petroleum gas is widely used in both OEM and aftermarket conversions for cars and light trucks.

LPG is a mixture of butane and propane, but the proportions vary wildly. I believe it is often 100% one or the other.

It is not corrosive as a liquid or as a gas, at least as far as 'normal' engine components go. It is actually a very easy fuel to use in its gaseous form. Most aftermarket conversions are set far too rich, but the OEM cars are easy to calibrate to normal standards.

DI of liquid propane would be a bit tricky, the nozzle would get very cold and you might get icing up. That sounds solvable.

The volumetric decrease when used as a gas is only 5% or so. In an installation that is designed to use this fuel that is such a piffling loss (easily made up by upping the capacity of the engine) that I would not expect anyone to got to the trouble of DI to get around it. Retrofitting DI to an existing SI engine sounds much too hard.

The main reason it isn't used more in Australia is that it is a 'waste' product from our oil-fields. If significant amounts of it are being used then the price will increase - it has doubled in the last 4 years since OEM cars became available. This rather destroys the immediate economic advantage. 4 years ago petrol was about 70c/litre, LPG was 19 c/litre. One litre of LPG gets you roughly 70-80% as far as a litre of petrol (roughly). Off the top of my head we charge about 800 bucks for a factory fit LPG single fuel installation, rather more for a dual fuel rig.


Greg Locock

RE: Propane

thanks greg!

RE: Propane

Gaseous fuels (Natural Gas and Propane) is my field of study, hobby, occupation, and addiction!

Vapor fuels have been widely used, and is the worlds most common alternative fuel.  Propane leads the field here with more than 5 million vehicles worldwide.  Fuel quality varies as to its purity and concentration.  Greg Locock is correct with Australia being one of the pushers for gaseous fuels, and a lot of the worlds leading technology originates there.  I envy the price differences, here in the US, propane is close to gasoline in fuel cost per mile.

In the US, propane must (should) comply with the fuel standard HD-5, roughly meaning that fuel marketed as LPG should be at least 90% propane, traces of ethane, propylene, normal and iso butane, and other minor fractions gasses.  In other parts of the world, higher percentages of butanes are allowed, up to 60%.

Propane has 104 octane, allowing for easy use in engines with compression ratios in the 10:1 range without much worry.  Propane is non corrosive and reverts to a zero pressure liquid at –44 Deg F.

Liquid injection is in existence, to a limited extent here in the US, but more widely in Europe and Australia.  There are few, if any, generic installation kits, as most of them are highly developed and calibrated for specific applications.

Vapor fuel carburetion is common, but volumetric efficiency suffers, reducing power often in the 15 to 20% range mentioned already.  Liquid injection vastly improves this by increasing the charge air density (as the liquid propane is metered into the intake manifold, just above the intake valve, it drops temperature tremendously, increasing the density of incoming air).  Some tests have shown Liquid Propane Injection power levels equal to gasoline.

Direct in-cylinder injection is a bit away, but I personally know of some projects with LPDI.

RE: Propane

hi franzh!!

thanks for your reply. but i still dont understand that why we dont abundantly use propane then. good octane rating, low emissions and comparable cost. the volumetric efficiency deficit can be avoided by using liquid propane in PFI engines, right?

how is liquid propane prevented from vaporizing in a PFI engine rumming on liquid propane?
also as the octane rating is higher comapred to typical pump gasolines can the engine be run at higher compression ratios? that will maybe offset the volumetric efficiency deficit.


RE: Propane

Propane will vaporize almost instantly as it reaches the absolute pressure (manifold vacuum) present.  Quick thought would place propane back into the liquid state as it is compressed during the compression stroke, but the ambient internal temperatures present inside the combustion chamber keep it in vapor state.  With a port fuel injected engine, we want it to vaporize to absorb the latent heat of the incoming air.  Liken this to the air conditioning system with an expansion valve.

Why isn’t propane used more by the OEM’s?  Look at the Fortune 500 top ten, Exxon/Mobil & General Motors.

The public has also some to blame; they don’t want to try something new.  Remember the unleaded gas introduction during the mid 1974 model year?  All sorts of blame was placed on the fuel, forgetting that autos always need service, and still do after a new fuel is introduced.

Ford had the Granada w/LP as an option in 1981, but very poor sales and a lousy engine combination ruined that chance.  Ford also has the F-700 up to 1997 then discontinued it.  Ford released a hybrid F-150 in 1996 that was a flop, then re-released an LP option in 1999.  It is still in limited production, and is not too bad an option.  GM and Chrysler never released a factory LP option.

Increasing compression to take advantage of the octane works well, as long as we stay out of the NOx region.  This places the engine performance right at the equal of gasoline, but gasoline can NEVER be used in this engine!

There is plenty of propane to go around, and it is mostly produced in the US, minimizing import oil and complying with the EPACT law of 1992.  Wish everyone would consider it, its actually fun to play with, within reason!

RE: Propane

Some thoughts on why propane likely is not used over gasoline:

In terns of fueling infrastructure, Propane fueling facilities are not as numerous as gasoline fueling facilities.  Propane fueling is also more difficult because it is stored under pressure to store as a liquid.  Gasoline is not pressurized in the storage tank.  Because of the pressurized storage for propane, the fuel storage system is more costly, and more dangerous when refueling and incase of impact/puncture.

Vehicle range is also lower than for gasoline.  Although the heating value / mass is the same as gasoline, the density of liquid gasoline is 50% higher than liquid propane.  A higher compression ratio will help, but not enough.

I have nothing against propane, except these short comings versus gasoline.  I used to work on natural gas engines.  These never took off for similar reasons, but of a higher magnitude.  I do know that Cummins offers (or at least did offer) a 5.9L LPG engine for heavy duty vehicles.

RE: Propane

I generally agree with Firelovers observations.  As a staunch advocate of gaseous fuels, I strongly encourage their use and additional research into non traditional applications.  One recent development is using propane as an energy source for fuel cells!

I was a consultant during the design and prototype development of one of the 5.9B series Cummins and other Propane and Natural Gas engines.  It is in wide use in airports as a shuttle engine, in forklifts and generator applications, school buses, city trolleys, dump and garbage trucks, delivery vehicles, and transit vehicles.

True, vehicle range is less per gallon than gasoline, about 15 to 20%, and yes, power is a bit less than gasoline, about 15% with modern engine controls.  BUT, with today’s technology, a gaseous fuel engine can produce transparent operation and emissions lower than gasoline.  Its simple chemical structure is more conducive to lower emissions.

Also true that propane is stored in pressurized containers, but groundwater contamination is not a problem if a propane leak were to develop, propane and natural gas vapors are non-toxic and not carcinogenic if breathed.

All things equal, if an engine were developed exclusively for propane use (compression, piston and chamber design, camshaft profile, and ignition timing) its power production can almost equal that of gasoline of the same displacement.  There is no cylinder wall whetting, almost no carbon buildup, no piston/ring washdown, no oil contamination, good cylinder fuel/air homogenization, relatively consistent combustion processes, etc.

In Texas, there are over 700 propane facilities that sell fuel to the public.  Propane is the third most used fuel in the world.

I am not a marketer of Propane, but am highly involved in research and training with gaseous fuels.  I strongly feel that with the correct incentives and applications, gaseous fuel vehicles can make a significant impact on domestic economy and reduce foreign oil imports, while reducing emissions and improve air quality.

Time to get off my soapbox.

RE: Propane

the other problem is that here in the UK nearly all new pick up trucks are only available as a DIESEL at least in 2000 when I bought one. And on a pick up truck theres room to put the tank with propane at  45c a litre and Diesel at $1.05 a litre I know which I would prefer  to run on but the manufacturers prevent this option being available in the UK.

RE: Propane

  I just attended the Bologna Motor Show which had a special section on alternative fuels, especially LPG. FIAT, among others, is selling bi-fuel vehicles with liquid propane injection as an option for about $2000.
 Someone I spoke with mentioned a Swiss and an Italian company as well as Bi-Phase here in the US as manufacturing liquid systems, but only for OEM aps.
   Is liquid propane injection available in the US from anyone other than Bi-Phase? I am interested in exploring the technology as a magazine tech feature, but their website paints them as less than friendly, and their system is not bi-fuel. Many thanks.

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