Drink Up! Alcohol as Motor Fuel
Soon after 1907, riders at Britain’s Brooklands Speedway discovered they could make more power on alcohol than they could on gasoline. At first this seems odd: gallon per gallon, alcohol yields only two-thirds as much energy as gasoline.
Where does the increased power come from? When alcohol evaporates it has a powerful refrigerant effect which cools the alcohol-air mixture so much that its density increases well beyond a gasoline-air mixture. Thus, the extra power gained from alcohol comes not from more energy in the fuel, but from the increased weight of extremely cold mixture that can fit into an engine’s cylinders.
Related: Adding Up the Octane Numbers
Alcohol’s Cooling Effect
That extreme cold also explains another beneficial feature of running racing engines on alcohol: they run much cooler than on gasoline. When a chemically correct fuel-air mixture burns, its temperature jumps up some 2,600 degrees Celsius above its original temperature. A mixture of gasoline and air, lacking alcohol’s extreme heat of vaporization (a measurement of how much energy is required to transform a quantity of a given liquid into a gas), may enter the cylinder at the temperature of a hot summer day and then be further heated by compression. On the other hand, an alcohol mixture enters at many degrees below zero. As a result, the peak temperature reached by the alcohol mixture is hundreds of degrees cooler than that of gasoline. This is how those strange alcohol-burning speedway engines, with their crew-cut head and cylinder fins, could survive: They were fuel-cooled.
This reduced temperature has the added effect of safely allowing an alcohol-burning engine to use a much higher compression ratio, which further increases power and torque. The onset of detonation or engine knock, an abnormal form of combustion that can be highly destructive, limits compression ratio in spark-ignition engines. (Fear not, ye owners of late-model bikes, as many have automatic knock detection and prevention.) Back when 10:1 was high compression for an air-cooled engine, riders could safely boost that to 14:1 for operation on methanol. Raising compression, by increasing peak combustion pressure, increases engine torque; the old rule of thumb is that peak combustion pressure in pounds per square inch is the compression ratio multiplied times 100.
Beginning in 1926, racers at the Isle of Man TT were required to use gasoline as fuel. Before that, alcohol was widespread, especially in record-setting attempts where its higher consumption was not a disadvantage. Alcohol’s use as a racing fuel continues to this day, especially in Australia.
Riders switching from gasoline to alcohol were advised to not only jet up to flow about 2-1/2 times more fuel, but to ensure adequate plumbing all the way back to the fuel tank. Thus, a 300 main jet would become roughly a 750.
Related: How Gasoline Has Changed Through The Years
Blended Alcohol Fuels
Today, it’s typical to see something like “contains 10 percent ethanol” on the pump at your local gas station.
Why does it say that, and what does it mean?
First, some basics: Methanol and ethanol are two different kinds of alcohol. Methanol is a partially burned molecule of methane gas, which consists of one carbon atom bound to four hydrogen atoms. The alcohol methanol is a methane molecule, one of whose hydrogen atoms has been replaced by an OH group. Methanol is poisonous to us humans, and is synthesized from methane or other petroleum hydrocarbons. Its common name is “wood alcohol,” and it is not being added to US transportation fuels.
Ethanol is a partially burned molecule of ethane, another colorless, odorless gas, and consists of two carbons bound to six hydrogen atoms. In ethanol, one of the hydrogens is replaced by an OH group. Ethanol is the alcohol in beer, wine, and spirits, where it is the subject of a lot of novel writing.
Now for the background. Back when the EPA was first given the mission of clearing up air pollution over US cities, a major perceived problem was the presence of many old-technology cars equipped with carburetors. In many carburetors, part-throttle mixture is controlled by tapered or stepped metering needles, working in orifices. As such autos aged, their metering needles and orifices rubbed together, causing the needles to become more slender, the jets to become bigger, and the resulting fuel-air mixture to become richer. This released unburned hydrocarbons into the air, which then acted as the raw material for photochemical smog.
I can vouch for the enriching effect of such wear: In the early 1980s, roadracer Nick Richichi drove a V-8 Chevy van that was returning terrible fuel economy and running poorly. I looked up the needle and jet part numbers, he bought and installed them, and with only that change his van ran as if it were 10 years younger.
Related: A Real World Look at Alcohol in Your Tank
MTBE, E10, and Today’s Gasoline
The EPA knew that most people weren’t going to identify, buy, and install new carburetor parts, so they decided to lean out these rich-running carbureted engines by adding lower-energy fuels to pump gasoline. The material they originally chose was MTBE (methyl tertiary butyl ether), and special plants were built to produce it. Adding 10 percent MTBE (which, like alcohol, also has two-thirds the energy content of gasoline by volume) caused the overall mixture to become a bit more than 3 percent leaner. Raising the MTBE content to 15 percent brought the enleanment to 5 percent.
As soon as MTBE was established as a pump-fuel component, it was discovered in groundwater and in drinking-water systems, having leaked from older underground tanks. Next, it turned out that soil bacteria didn’t metabolize MTBE, so it persisted. A moderate but manageable scandal ensued. MTBE was then replaced in pump gasolines by 10 percent ethanol, what we know today as E10.
This moderate enleanment didn’t hurt rich-running older cars with carburetors, and later-model vehicles with closed-loop fuel systems easily self-corrected their mixtures. The engines at risk were those jetted for maximum power on normal gasoline; on the new fuel these would be running lean.
As parts of the US added higher percentages of ethanol the effect became worse.
Some owners claim that their engines have been damaged by lean operation on gasoline/ethanol blends. On the one hand, we can argue that gasoline users should inform themselves about recent changes to fuel and read the ethanol content messages on gas pumps. On the other, we are creatures of habit. In the past, distracted motorists (“We’re all so busy now…”) would on occasion pull up to an unoccupied pump and unwittingly fill their tanks with diesel instead of gasoline. A change to the fuel-filler dimensions ensures that diesel pump nozzles will not physically fit into a gasoline-burning auto now, protecting us from ourselves.
Water, Corrosion, Morals
Another potential problem of alcohol in gasoline: so-called “water bottoms” may form in storage tanks as a result of alcohol’s ability to absorb moisture from the air. If a slug of water gets into your tank, it may cause unexplained erratic running as the heavier water slides around on the bottom, occasionally sending a bit into your fuel line. The next time you’re at your local airport, watch the light-aircraft pilots take samples from their fuel tank drain cocks to check for water during their preflight checks. Nasty to have your engine conk just after takeoff.
Yet another potential water-related problem caused by ethanol or ethanol-water mixtures in older engines is fuel-system-component corrosion.
A further possible objection to the addition of ethanol to pump gasoline has to do with morals and ethics. About 40 percent of the US corn crop now becomes ethanol for use in transportation fuel. Should we burn food when some of the world’s people haven’t enough to eat?
It might be nice if life were simpler, but it’s not going to happen.
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