Steam tractors could be
described as the ultimate in alternative fuel tractors. They’d run on almost
anything that would burn, including wood, sawmill slabs, sawdust and shavings,
“hog” fuel, coal, coal slack, kerosene, oil, heavy oil and even straw (the
burning of which was highly developed and quite popular out West from the late
1890s through about 1915).
But for all that versatility
that lowered a steam engine’s fuel cost, other operational costs far
overshadowed those savings, so when internal combustion engine tractors
achieved reliability, steam tractors quickly faded into obsolescence. The
internal combustion engine has ruled the ag power market ever since, but not
always as a gasoline burner.
By 1910, refining technology
still produced only a limited yield of gasoline from crude oil, and its growing
demand as automobile fuel kept gas prices high compared to that of kerosene and
heavier fuels. For that reason, many early tractor operators, particularly
those with large machines, searched for tractors capable of consuming heavy,
cheaper fuels. Efficient kerosene burning made for great advertising copy; just
look at Rumely OilPull ads from that era.
At first, the most common
alternative fuel was kerosene, which was produced from both crude oil and coal.
It cost a fraction of gasoline yet, when burned efficiently, produced
approximately the same horsepower hours per gallon as gasoline. (Horsepower
hours/gallon is a fuel conversion efficiency value that eliminates engine size
from consideration, thus making the result from a 100 hp engine comparable,
straight across, to one from a 10 hp engine.)
But kerosene has its
drawbacks. Mainly, it does not vaporize as readily as gasoline, and it has a
much lower octane content. That usually meant intake air and the intake
manifold had to be heated to improve vaporization, the combustion chamber had
to be carefully designed and kept clean to prevent knock, and for some engines
(Rumely OilPull and the early John Deere D, for instance) water was injected
into the cylinders to moderate combustion so as to further prevent combustion
knock. These engines do not “burn” water, as some people think. The addition of
water merely moderates the combustion rate to reduce knock and prevent engine
damage. The trade-off, though, is that water injection reduces overall engine
Each solution to these fuel
considerations came with its own drawbacks, increasing engine complexity and
requiring more skill and attention from the operator. As oil-refining
technology improved, gasoline yield increased and gasoline prices fell in
comparison to prices for kerosene and oils. Soon, the extra complexity of
operating on kerosene no longer made sense financially, and kerosene faded as
an ag fuel.
The first tractor tested by
the University of
Nebraska Tractor Test Laboratory
in 1920 was a kerosene-fueled John Deere Waterloo Boy Model N. The last
kerosene tractors tested, in 1934, were both International Harvester models: a
Farmall F-20 and a W-12. Kerosene remains, however, the dominant fuel powering
jet aircraft and turbine engines. You can sometimes smell it on airport
Distillate and tractor fuel
produced from crude oil are similar to kerosene, and like kerosene and stove
oil, distillate/tractor fuel requires air preheat and ongoing manifold heat to
vaporize properly for spark-ignited engine combustion. Lower compression than
with gasoline is required to prevent combustion knock and potential engine
damage. A lower compression ratio inherently reduces engine efficiency, which
explains why multi-fuel engines tend to have more thirst for gasoline than
straight gas engines in the same tractor model. Like kerosene burners, these
tractors have both a main fuel tank and a smaller (gasoline) tank for starting
The University of Nebraska
tested distillate (multi-fuel) tractors from 1947 through 1956, the earliest
being John Deere Models B and G, and the last being Deere Models 420, 520 and
Stove oil/no. 1 heating oil
Also produced from crude
oil, these fuels are roughly equivalent to no. 1 diesel (except they are dyed
red and you will be fined if the authorities catch you burning this fuel —
which is exempted from highway fuel taxes — in your on-road vehicle). Like
kerosene and distillate/tractor fuel, stove oil/no. 1 oil requires intake air
preheat and ongoing manifold heat to vaporize properly. Lower compression than
with gasoline is required to prevent combustion knock and potential engine
Heavy fuel (distillate,
tractor fuel and heating oil) consumption in spark-ignition engines dwindled in
the mid- to late-1950s as gasoline prices continued to fall and diesel engines
Liquefied Petroleum Gas (LP
or LPG) refers to butane or propane refined from well gas, or a mix of the two.
Earlier, the term referred primarily to butane, but it later swung to propane.
Today, butane is seldom mentioned in the market.
Both butane and propane
rapidly turn to vapor at normal temperatures and atmospheric pressures. That
means it must be shipped, stored and handled under pressure. As a result, leaks
are dangerous in closed buildings and propane should only be handled by trained
personnel. An inadvertent spray of LP, for instance, can cause immediate and
A second drawback is that
propane tends to collect in low areas, raising the potential for fire and
explosion. Additionally, each gallon of LP contains only 70 percent of the
heating value of gasoline: It takes almost 1-1/2 gallons to do the work of 1
gallon of gasoline, and fuel tanks must be 50 percent larger to get the same
amount of work done. Accordingly, propane is cheaper per gallon, even today.
Because LP tanks must be
cylindrical, getting enough tank capacity positioned under a tractor’s hood was
a challenge. Most LP tanks laid flat and bulged out through the hood, although
some were placed behind the driver’s seat (such as with a large Case tractor)
or ahead of the radiator (as in John Deere “New Generation” tractors).
Propane/LP has higher
equivalent octane content than gasoline, so for best efficiency it requires a
higher compression ratio than gasoline, usually one point higher (for example,
8.5 vs. 7.5:1 in Continental-built Massey Ferguson
engines). Running LP in an engine with gasoline compression ratio does no
damage, you just won’t get good fuel economy. Additionally, propane engines
usually require hardened valves and valve seats to give valve life equal to
that of gasoline engines.
Market shifts drive change
Beginning in the early
1950s, LP became readily available at prices that made its drawbacks easy to
overlook. In oil-producing areas where LP was particularly inexpensive (like Texas, Oklahoma and the
southern Midwest), farmers rushed to convert
existing tractors to LP and purchase factory-built LP burners.
Minneapolis-Moline advertised LP tractors as early as 1950. By the mid-1950s,
most tractor manufacturers offered LP-powered tractors. Of the major
manufacturers, Minneapolis-Moline probably produced the highest percentage of
their tractors as LP burners. The first four-wheel drive tractor over 100 hp
was the Minneapolis-Moline G706, available in both LP and diesel, but not
gasoline (also sold as the Massey Ferguson MF-97 FWA).
By the mid- to late-1960s,
though, propane prices had risen and diesel engine technology had improved
(solidified by the advent of turbocharging) to the point where LP provided
little, if any, economic advantage to offset its disadvantages. Its usage waned
as the new turbocharged diesels took over.
Today, LP-fueled engines are
most commonly used in forklifts, warehouse tractors or other machines (such as
floor buffers) operating inside buildings. Properly tuned propane fueled
engines produce no carbon monoxide, and unlike diesel engines, no soot.
Bottom line demands
The historical use of
alternative fuels in farm tractors illustrates farmers’ ingenuity and
willingness to cut operating costs whenever fuel prices and equipment
technology made a change feasible. Turbo-diesels may dominate ag power today,
but what will become the fuel of choice tomorrow? FC
Chuck Lyons is a retired mechanical engineer living
near Spokane, Wash.
He is a self-described “equal opportunity collector” of steam tractors, trucks,
cars, crawlers and all colors of wheel tractors. Call him at (509) 276-6366 or