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A flammable liquid in its liquid state
will not burn. It only will ignite when it vaporizes into a gaseous state.
All flammable liquids give off vapors that can ignite and burn when an
ignition source such as a lighted cigarette or spark is present. How easy it
is for a liquid to vaporize can be determined by looking at its flash point.
The flash point of a liquid is the temperature at which a particular
flammable liquid gives off vapors (vaporizes) and therefore can ignite. The
flash point differs for each type of flammable liquid. Kerosene has a flash
point of 110 degrees Fahrenheit. Gasoline has a flash point of -40 degrees.
This means that at 110 degrees or higher kerosene gives off flammable vapors
and can ignite. However, gasoline requires a temperature of only 40 degrees
to vaporize to cause an explosion or fire. This means that when the
temperature is freezing, gasoline still vaporizes and can cause an explosion
and/or fire. At the same temperature, kerosene cannot ignite. Liquids such
as gasoline with a flashpoint below 100 degrees are called flammable
liquids. Kerosene and other liquids with a flash point above 100 degrees are
referred to as combustible liquids.
The vaporizer coil raises the
temperature of the liquid fuel to above its flash point so that the fuel is
vaporized. Originally Stanley used gasoline for both the pilots and burners.
The Stanley’s selected gasoline due to its molecular structure giving it the
property to vaporize easily. There were other flammable liquids that they
could have selected form but gasoline was plentiful, produced a lot of heat
per unit volume burned, and could be easily handled with the simple plumbing
hardware available at that time.
As more and more Stanley cars were
produced the use of gasoline to fire the burner had to be rethought.
Gasoline’s low flash point also made it too hazardous for use with an
semi-open flame burner design and the Stanley’s moved to using kerosene to
fire the burner. This change necessitated a longer vaporizer coil because of
the additional heating needed to vaporize kerosene over gasoline. Thus in
1913 the change to kerosene was made for the burner while the pilot
continued to use gasoline for fuel. Another advantage of kerosene fuel is
that is provides about 12% more heat per gallon as compared to gasoline.
More heat means more steam and faster steaming per gallon of fuel carried by
the car.
A 3/8" diameter pipe
is commonly used for the burner vaporizer. The proper length and
positioning of the vaporizer is important to the proper vaporization of the
fuel. If the gas leaving the nozzles is essentially clear it is being
properly vaporized. If the gas leaving the nozzles has a foggy
appearance then it is considered "wet" in that it contains a high degree of
liquid in the vapor. If the gas leaving the nozzles is totally
transparent it might be an indication that the gas is too hot and possibly
being superheated. Ideally when the vaporization is correct the gas
leaving the burner nozzle should have the appearance of a very faint haze.
If the vaporizer tube is too short
all of the liquid fuel will not be converted to gas and the result will be a
very wet gas flow from the nozzles. This wet gas flow will not only
waste fuel it will also cause the burner to back-fire (ignite the air-fuel
mixture in the mixing tubes which will quickly damage the mixing tubes and
grate). If the vaporizer tube is too long then the gas will become
superheated and carbon deposits will form on the inner wall of the vaporizer
tube. These carbon deposits will break free and travel to the small
orifice of the burner nozzle and plug it up. Generally an optimum
length for the vaporizer tube is around eight feet.
Proper positioning of the burner
vaporizer coil above the burner grate is also important. The vaporizer
coil should be located about an inch or so above the top of the grate so
that it receives maximum heating from the fire. As in the case of the
length of the vaporizer coil, the position of the vaporizer coil in the
flame will contribute to the gas being either wet or superheated.
Often if the gas leaving the nozzles is wet or there is a tendency for
carbon to choke the burner nozzles the repositioning of the vaporizer coil
in the fire will correct the situation and it won't be necessary to lengthen
or shorten the burner vaporizer tube.
Vaporizer coils are exposed directly
to the heat of the fire and therefore should be made of material which will
not only withstand the extreme temperature but also will not deform under
the 140 PSIG pressure of the fuel entering the vaporizer coil. A
vaporizer is generally constructed of 1/4" pipe.
Heavy-walled seamless, Schedule 80, 304 stainless steel pipe is often chosen today as the material of
choice for making a vaporizer tube.
To held distribute
the heating effects of the vaporizer tube on the fuel flowing through the
coil a stranded length of wire is inserted in the end of the vaporizer coil.
This length of wire should fill at least 2/3rds of the length of the pipe
although some Stanley owners have cable the full length of their vaporizer
coil. The outside diameter of the vaporizer wire should be very nearly the inside
diameter of the vaporizer pipe.
Type 316 Stainless Steel Wire Rope, 7 X 19 Strand Core, 3/16"
diameter is often chosen for this application. To prevent fraying the
ends of the cable are TIG/MIG welded together making sure that the weld
doesn't increase the overall diameter of the wire so that the wire still
will slide freely into the vaporizer pipe.. For
Stanley burners the cable is generally inserted in the nozzle end of the
vaporizer tube while for Cruban burners the cable is inserted in the fuel
supply end of the vaporizer tube.
If the proper length of vaporizer
tube is used and it is positioned optimally in the fire there will be little
carbon build-up on the interior of the vaporizer tube and on the surfaces of
the wire. However, in time carbon will collect and the wire will need
to be pulled from the vaporizer tube. The burner nozzles are also
removed to allow for cleaning of the vaporizer tube. The tube can then
be flushed with fuel (by briefly opening the fuel valve) to wash it clean of
loose carbon deposits (this is obviously done when the car is cold and there
is no flame around). Air can be used to blow the fuel out of the
vaporizer tube before the wire is replaced.
Some owners have
chosen to connect a steam line, often referred to as a "steam enema", to the
fuel supply line for the purposes of cleaning the vaporizer tube.
Before blowing down the car the vaporizer tube wire is removed along with
the burner nozzles. A steam supply valve is opened and the steam rushing
through the vaporizer tube quickly cleans it. Once the car has cooled
the wire can then be reinstalled along with the nozzles.
Another cause of vaporizer carbon
build-up is a leaking steam enema valve. If the steam enema is leaking
the steam rapidly cools the superheated fuel before it vaporizes and carbon
black is formed. The carbon black deposits quickly plug the vaporizer
and a lack of fuel flow results. An easy tell-tail that the steam
enema valve is leaking is a continued wisping of what appears to be
vaporized fuel exiting the burner nozzle(s). When the burner is shut
down using the burner valve on the car's dash, any residual vaporized fuel
remaining in the vaporizer coil should bleed off in a minute or so and the
burner nozzles should not display any "leakage". If there is a
continued flow of "gas" from the nozzles 5 minutes after the burner is shut
down then checking to see if the leakage ignites will determine if the fuel
valve is leaking or the steam enema valve is leaking. In either case
prompt corrective action is needed before the car is operated.
Occasionally some bad fuel can cause
the vaporizer to actually choke nearly solid with carbon and other deposits and block the
flow of fuel. In a like manner if the vaporizer is improperly
positioned and superheats the gas such that carbon is readily formed, the
vaporizer tube can become choked. When this occurs it is necessary to
remove the burner nozzles and pull the vaporizer wire (pulling the wire can
be difficult if the carbon buildup is especially bad). The burner
should be dropped from underneath the boiler and the vaporizer tube removed
to an outdoor area for burning out.
Using an oxygen-acetylene torch (a
propane torch or similar isn't hot enough) the end of the vaporizer tube is
heated cherry red for a three to four inch length (be careful not to melt
the tube!). When the tube is glowing red hot turn off the acetylene
flow to the torch and place the nozzle end of the torch into the end of the
vaporizer tube so that the oxygen will flow through the tube. The
oxygen flow will cause the carbon to burn vigorously and you may observe a
shower of sparks and burning bits of carbon jetting out the opposite end of
the vaporizer tube. For really bad carbon deposits one can watch the
progress of the burning carbon as it will heat the vaporizer tube cherry red
at the flame boundary within the pipe and the cherry red zone will moved
along the length of the pipe. When all sparks and flame cease coming
from the vaporizer tube it is an indication that all the carbon has been
burned out. The vaporizer coil can be allowed to cool and then
reassembled to the burner and the burner returned to the underside of the
car. |
