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 efficiency.
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 runways.
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 and warm-up.
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 620.
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 damage.
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 gained popularity.
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 severe frostbite.
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.
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.
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 email: firstname.lastname@example.org.