Brazil's Diesel Fuel Alternatives

Brazilian researchers explored a number of diesel fuel alternatives in the late 1970s/early 1980s, including ethanol and vegetable oil.
By the MOTHER EARTH NEWS editors
July/August 1980
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A small percentage of the Sao Paulo city bus fleet has been operating on alcohol as a diesel fuel alternative since last year with excellent results ... and far fewer toxic exhaust emissions.

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Not long ago, two of MOTHER EARTH NEWS' editors returned from Brazil, where they had been investigating that country's massive effort to replace virtually all of its presently imported petroleum fuels with homegrown energy in the next decade or so. Clearly, the forward-thinking South American nation sees the "shape of things to come" ... and has chosen to take a positive course of action rather than merely fret about the future.

One of the major concerns of the Brazilian people is the availability of diesel fuel, since 80% of that country's goods (and most of its commercial passengers) are transported by heavy trucks and buses. Because even less diesel oil than gasoline can be gleaned from a barrel of crude petroleum, it's easy to understand why efforts are being made to look for viable domestic diesel fuel alternatives.

Appropriately enough, Mercedes-Benz (which supplies much of South America with diesel vehicles) of Brazil has been busily engaged in researching alternative fuels since early in 1973 ... and as of September 1979 has been testing its experimental fleet commercially, in the field, with excellent results.

Naturally, because Brazil has been so heavily involved in what they refer to as the "pro-alcohol" program, engineers at M-B have been primarily interested in running their diesel engines on ethanol ... but they've also been actively working with two other types of fuels that show great promise: a combination of diesel oil and gasoline, and a mixture of vegetable oil and diesel fuel.

How They Did It

Standard diesel fuel has specific properties that make it suitable for use in self-firing internal combustion engines. The "liquid energy" provides needed lubrication, ignites easily, flows freely, burns with a minimum of residue, resists pre-ignition, and is relatively nonpolluting. Ethanol meets all these requirements but two: It doesn't have the lubricative qualities of petroleum distillates, and its cetane number (which is used to indicate the ability of a fuel to ignite quickly after being injected into the combustion chamber) is only about 10. (A diesel engine requires a fuel with a minimum rating of 45.)

In order to provide the necessary lubrication to the engine's injector pump, the Brazilian scientists merely routed an additional oil line from an existing fitting in the block, then on to a filter, and then into the pump itself. At the same time, the researchers installed a return tube to allow the pressurized engine oil to drain back into the crankcase.

The system not only furnishes lubrication to the pump components, but because a small percentage of oil (less than 0.1 % of total fuel volume) is introduced into the liquid alcohol, the injector plungers also get a friction-reducing "bath." (Since the volume of oil in a diesel engine crankcase is great and because such powerplants normally receive frequent oil changes, there's no danger that the minute amount of lubricant "borrowed" from the oil sump would ever drain the "host.")

In addition to setting up a system to supply lubrication to the pump, the Mercedes experimenters also enlarged that mechanism's control jet a simple "one wrench" adjustment in order to provide 50% more alcohol to the engine (which is necessary because of the difference in heat values between ethanol and diesel fuel). Extended tests indicate that the fuel distribution system doesn't suffer deterioration or cavitation (though some of the assembly's zinc coated parts were recovered with tin as a precautionary measure). And engine durability is, studies indicate, unaffected ... because although horsepower and torque are increased as much as 20% when burning ethanol, the additional stress is well within engine design limits.

Once the powerplants were modified to accept homegrown fuel, the only area left for the South American scientists to research was the composition of the mixture itself. To cure the cetane problem, engineers decided to try adding "diesel ignition improvers" to the ethanol in an effort to reach a happy medium between good performance and reasonable cost. The research bore fruit: Not only did every cetane number raiser perform well with alcohol, but better yet, several of them (butyl nitrate, isoamyl nitrate, diethylene nitrate, and ethylene glycol nitrate) can be extracted directly from domestic sugar cane at an acceptable price.

Two Other Alternatives

Besides working wholeheartedly on an alcohol-based diesel fuel substitute, the Brazilians have been giving considerable attention to the other pair of liquid energy choices mentioned previously. Because there is—believe it or not—an excess of gasoline in Brazil (directly due to the success of the nation's pro-alcohol program), energy officials have been stretching their diesel fuel supplies by blending in the lighter volatiles at the refineries. This has the direct result of slightly lowering the flash point and heat value of the Brazilian-style truck fuel, but by the same token it increases the nation's diesel reserves by nearly 20% ... and, fortunately, vehicle powerplants needn't be altered to burn the mixture.

Perhaps even more important—because renewable liquid energy resources are involved—is Brazil's vegetable oil fuel research. Mercedes Benz has been running a mixture of 70% diesel fuel and 30% soybean oil in factory stock engines, with promising results. Another series of tests indicates that many types of domestic vegetable and plant oils—when refined—can be used directly in diesel engines ... possibly without additives (though some of the organic fuels yield greater than normal amounts of carbon residue, which would result in more frequent engine maintenance).

Today Brazil... Tomorrow ...?

Although the research being conducted on the above-mentioned fuels is by no means complete, experimental Sao Paulo city buses have chalked up a collective total of nearly 20,000 miles to date, and test engines at the Mercedes factory have logged the equivalent of over 300,000 miles ... in each case with no problems. In the near future, another 200 ethanol powered motor coaches should be put "on line" in the city.

What this all boils down to, of course, is that Brazil is working steadily and successfully toward energy self-sufficiency ... and there's no reason why we can't do the same!

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