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"Notes from the Unit Shop"

Kevin O'Connor's advice for the beginning small scale live steamer

 

What is the Best Fuel for my 

Gas Fired Gauge One

 

The best fuel for a gauge one gas fired locomotive is the one that is safe to use, performs best over a wide range of temperatures, and is available at the lowest cost.  I have arbitrarily decided not to consider propane (Pn) as a fuel for gauge one locomotives because of its dangerously high container pressure at any reasonable temperature.  All manufacturers of gauge one locomotives specifically caution against the use of propane as a fuel in their locomotives.  I am fully aware that some model engineers have had great success with propane as a locomotive fuel, but that has been in locomotives specifically engineered to accept the very high pressures inherent in the use of propane as a gauge one model locomotive fuel. 

 

Temperature performance is important because the liquid gasses that are used in gauge one locomotives are dependent on temperature in order to vaporize properly at a pressure high enough to be useful in the locomotive's burner.  If the temperature drops too low, vaporization slows down and the pressure at the burner's nozzle drops.  In the case of butane (Bn) this drop can be so great that the burner refuses to burn much below 60 F without additional heat in the form of a hot water bath in the tender or a cab mounted gas tank that absorbs heat from the locomotive's backhead.  Even if the outdoor temperature is above 60 F the vaporization of the liquid gas in its storage tank will cause it to lose heat energy.  If the storage tank is too well protected from the outside air, and little additional heat energy can reach the tank, the gas pressure will drop until some steady state of reduced temperature vs. pressure is reached.  This condition explains why many locomotives start off their running pulling strongly only to slow down or struggle by the end of the run.  It has nothing to do with the supply of liquid gas in the container, but it has everything to do with the temperature of the container as it affects the gas pressure at the nozzle.

 

Most of the liquid gas containers that are used to fuel gas one locomotives are really designed to fuel camping stoves, illuminating devices and heaters for campers, backpackers, hunters, and other outdoor users.  The manufacturers who cater to this market have a problem similar to the one that plagues gauge one locomotives - outdoor temperature.  Liquid gas evaporation is just as important to the proper operation of their appliances at it is to the burner jet in gauge one locomotives.  As the out door temperature drops, the efficiency of their products fall off and, in days past, the cold weather outdoorsman turned to gasoline and kerosene fuels when the weather turned frosty. 

 

The liquid gas appliance manufacturers look for a gas that would perform better at lower temperatures, and the petroleum industry responded by developing isobutane (Bi) liquefied gas to replace the butane liquefied gas then in service.  Isobutane is an isomer of butane.  That means that it is has the same number of hydrogen and carbon atoms, but that they are rearranged in a different order within the molecule.  This change results in a product that exerts more pressure within its container at any given outdoor temperature than regular butane.  Although isobutane boosts the performance of outdoor appliances it has one drawback and that is price.  The petrochemical industry changes more for isobutane than for butane because of the cost involved in juggling the atoms of hydrogen and carbon. 

 

It had been long known in the petrochemical industry that it was possible to mix two related gasses together (such as butane and propane) and to produce a hybrid gas having a container pressure somewhere between the two, depending on the ratio of one gas to another.  This approach had a problem insofar as the combined liquid gasses would not remain in a homogeneous state, but would disassociate themselves over a short period of time.  In effect what remained was a container half full of propane and half full of butane.  This meant that instead of having a container of liquid gas at some median pressure it would revert to the pressure of the propane for the first portion of the use and drop to the pressure of butane for the remainder of the use.

 

I am told that the push in the United States to free the atmosphere of of Freon products used as propellants in aerosol containers convinced the petrochemical industry to revisit the blending of various liquid gas products.  They saw a potential market for these products as a replacement for the soon-to-be-banned fluorocarbons, but the problem of disassociation still loomed. 

 

At this point the science of cryogenics entered the equation.  Cryogenics is the study of the behavior of substances at super low temperatures - somewhere down around absolute zero.  It was found that if two liquid gasses were blended at a very low temperatures, somewhere around their freezing point, that when they were allowed to heat up to room temperature they would remain stable and exhibit pressure characteristics proportionate to the ration in which they were mixed. 

 

The result of the work was a new family of aerosol propellants and the first of the propane and butane liquid gas products for the cold weather outdoorsman.  There is one caveat.  Cryogenically blended liquid gasses will, over time, disassociate them selves in the container storing them is subjected to temperatures below 20 F for extended periods of time.

 

These blended products are now available for use in gauge one locomotives, but they tend to come in containers that do not accept the standard screw-on decanting valve that is used on the butane or isobutane containers.  There are exceptions, regional in nature, such as the imported containers from England.  I have been told of mixtures as high as 40% propane to 60% butane, but I have never seen them.  I suppose that their performance is superior to isobutane, but I suspect that their cost is higher per unit of measure.

 

Jim Hadden, who regularly steams all winter in Utah, has been using a liquid gas product sold under the brand name Gaz™, which consists of a 20% propane and 80% butane mix.  I started using it last winter here in Sacramento.  The advantage of using Gaz over isobutane is two fold; it works better in cold temperatures because of its higher container pressure (see figure one) and it is far less expensive to purchase per unit of measure. 

 

I pay 1 cent per gram for Gaz (1# container) vs. 1.5 cents per gram for isobutane in my local outdoor supply store.  Unfortunately, the Gaz container is one that has now screw threads and it will not accept the standard decanting valve.  Both Jim and I were using a Rube Goldberg setup to milk the Gaz container, but we felt that the process was too dangerous (frozen fingers) for publication.  There is now a decanting valve available for the Gaz container. 

 

My hope is that this discussion of liquid gas fuels for gauge one locomotives sheds some light on the folklore that seems to surround them in conversation at steamups. 

 

 

 

(This article was originally published in "Steam in The Garden," Vol. 6, No. 4, Issue No. 34, July / August 1996)  Appreciation to both Kevin O'Connor and Ron Brown for permission to to post this feature on the Southern Steam Trains website.)

 

 

 

 

 

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