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Making Alcohol Fuel

Mother’s Alcohol Fuel Seminar
© The Mother Earth News, 1980

Alcohol as an Engine Fuel

Before you begin to convert your automobile or truck engine to use alcohol, it's important that you understand the properties of - and the differences between - the two fuels.

Gasoline is a complex mixture of hydrocarbons ... substances comprising just hydrogen and carbon atoms. These hydrocarbons can appear in all forms (as a gas, liquid, or solid), but for our purposes, we're concerned with the fuel in its liquid state.

To derive various hydrocarbon fuels, the industry merely refines crude oil (made many millions of years ago as a result of geological and biological cycles) and draws off the desired product at a certain temperature and pressure. Hence there are the lighter, gaseous fuels such as butane, propane, and ethane ... the liquids like octane, pentane, and hexane ... the heavier, oily liquids such as kerosene and fuel oil ... and so on all the way down through waxes and finally solids.

Gasoline as we know it is a combination of octane, benzene, toluene, various other aromatics, tetraethyl lead, detergents ... and compounds of sulfur, phosphorus, and boron. Because of this complex mixture of ingredients - and because the refineries vary the blend to suit climate, seasonal changes, and altitude - it's difficult to choose a "representative" sample of gasoline for comparison purposes. Nonetheless, the figures that are given in the "Properties of Gasoline, Ethanol, and Methanol" chart which follows are fairly typical of average high-test automotive gasoline. [Chart not included.]

Alcohol, on the other hand, has to be manufactured ... in our case through fermentation and distillation processes. Because of the steps involved in its manufacture, alcohol has always been more expensive than gasoline to produce. But now, with dwindling crude oil supplies, the price of gasoline is skyrocketing ... and soon gasoline itself will probably have to be synthetically manufactured, at a cost far greater - since the production process is much more complicated than that of alcohol.

Alcohol compounds are also hydrocarbons ... but in alcohol, one of the hydrogen atoms has been supplanted by a hydroxyl radical (hence the OH symbol), which is an oxygen atom bonded to a hydrogen atom. Alcohols, too, take many forms and have various levels of complexity, but we're concerned mainly with ethanol (grain-derived alcohol) and - just in passing - methanol (wood- or cellulose-derived alcohol).

These two alcohols are the only practical alcohol fuels ... and of the two, ethanol is more economically feasible on a small scale. (The raw material used to make methanol - wood chips, garbage, or cellulose matter - is relatively inexpensive, but the manufacturing process necessary to produce methyl alcohol is economical only on an industrial level.)

On the surface, the difference between alcohol and gasoline might appear relatively minor: Alcohol contains oxygen, while gasoline doesn't. In reality, however, the dissimilarities are far more complex than that. Additionally, under compression - as is the case in an engine's combustion chamber - things get even more complicated ... but we'll get more into detail on these points later.

Regardless of the inherent differences between gasoline and alcohol, though, the fact is that alcohols make ideal motor fuels. The first practical internal combustion engine - patented by Nikolaus Otto in 1877 - ran on alcohol (gasoline had not been "discovered" yet), and the Model A Ford, produced from 1928 to 1931, was designed to burn a variety of fuels ... alcohol being one of them. In addition, Studebaker trucks built for export in the 1930's (and various domestic tractors sold both in the U.S. and abroad) were offered with either gasoline or alcohol fuel systems. (Indeed, at the start of the "motorized era", alcohol was just as common as - if not more so than - fossil fuels. But as time went on, the petroleum industry - which was organized and thus more powerful than the independent, often farm-based alcohol producers - lobbied successfully for the wholesale use of "superior" gasoline fuels. Strangely enough, in areas where petroleum had to be exclusively imported, or during time of war when gasoline supplies were rationed, alcohol suddenly became an excellent motor fuel again ... and was touted as such by the petroleum distributors who were selling it!)

Be that as it may, alcohol has characteristics that make it a natural engine fuel: [1] It has a high “octane" rating, which prevents engine detonation (knock) under load, [2] it burns clean ... so clean, in fact, that not only are noxious emissions drastically reduced, but the internal parts of the engine are purged of carbon and gum deposits ... which, of course, do not build up as long as alcohol is used as fuel, [3] an alcohol burning engine tends to run cooler than its gasoline-powered counterpart, thus extending engine life and reducing the chance of overheating.

At this point, we can detail exactly how these and other characteristics of alcohol affect engine performance.


Actually, when referring to alcohol fuels, the word "octane" does not apply, since octane (in its pure form) is merely the hydrocarbon in gasoline which is assigned the numerical value of 100 for fuel-rating purposes. The octane number given automotive fuels is really an indication of the ability of the fuel to resist premature detonation within the combustion chamber. (Premature detonation, or engine knock, comes about when the fuel/air mixture ignites spontaneously toward the end of the compression stroke because of intense heat and pressure within the combustion chamber. Since the spark plug is supposed to ignite the mixture at a slightly later point in the engine cycle, pre-ignition is undesirable, and can actually damage or even ruin an engine.)

Because a high compression ratio in an engine results in more power per stroke, greater efficiency, and better economy, it's easy to see why a fuel that resists pre-ignition even under high compression conditions is especially desirable ... and alcohol is, on the average, about 16 points higher on the research octane scale than premium gasoline.


The heating value of a fuel is a measure of how much energy we can get from it on a per-unit basis, be it pounds or gallons. When comparing alcohol to gasoline using this "measuring stick", it's obvious that ethanol contains only about 63% of the energy that gasoline does ... mainly because of the presence of oxygen in the alcohol's structure. But since alcohol undergoes different changes as it's vaporized and compressed in an engine, the outright heating value of the ethanol isn't as important when it's used as a motor fuel.

The fact that there's oxygen in the alcohol's structure also means that this fuel will naturally be "leaner" in comparison to gasoline fuel without making any changes to the jets in the carburetor. This is one reason why we must enrich the air/fuel mixture (add more fuel) when burning alcohol by increasing the size of the jets, which we'll discuss further in another section.


The volatility of a fuel refers to its ability to be vaporized. This is an important factor, because if vaporization doesn't occur readily, the fuel can't be evenly mixed with air and is of little value in an engine. Some substances that are highly volatile can't easily be used as a motor fuel ... and others, which have excellent heating value, aren't volatile enough to be used in an engine (such as tars and waxes).

Another point to keep in mind is that a very volatile fuel is potentially dangerous, because of the chance of explosion from heat or sparks. This is one reason why alcohol, with a higher flash point than gasoline, is a much safer automotive fuel ... especially considering that the average car's storage tank is really quite vulnerable.


Latent heat of vaporization is the phenomenon that results in an alcohol-powered engine's running cooler than its gasoline-fueled counterpart. When a substance is about to undergo a change in form (from a liquid to a vapor, in this case), it must absorb a certain amount of additional heat from its surroundings in order for the change to take place. Since alcohol must absorb roughly 2-1/2 times the amount of heat that gasoline does, and the heat naturally is taken from the engine block, the engine should operate at a much lower temperature ... in theory, that is.

What happens in reality is that the alcohol/air mixture doesn't have time to absorb all the heat it could during its short trip through the engine manifold. So instead of running 2-1/2 times cooler on alcohol than it does on gasoline (which, by the way, would not be desirable ... since an engine must retain a certain amount of heat to run efficiently), the engine operates at temperatures only slightly cooler - about 20-40 deg F lower, depending on the specific engine when using alcohol fuel.


When gasoline is burned in an engine, it produces carbon monoxide and other poisonous fumes ... mostly because of the fact that the fuel never combusts completely, and also because it's subjected to extreme temperatures and pressures. In addition, as we mentioned before, gasoline is a complex mixture of many substances ... and some of those substances are lead, sulfur, and other noxious materials. These, too, add to the contaminative effects of the engine's exhaust fumes.

Alcohol, on the other hand, burns much cleaner. Even though it, too, never combusts completely, the volume of noxious fumes is drastically reduced in an alcohol-burning engine ... because alcohol contains oxygen in its structure (which means more thorough combustion) but doesn't contain all the other pollutants necessary as additives in gasoline.

For comparison purposes, MOTHER's researchers ran tests on a 1978 Chevrolet taxicab ... which, operating in New York City, was subject to some of the most stringent pollution controls in the nation. (In order for cabs to be licensed, they must undergo - and pass - four scheduled EPA tests a year for carbon monoxide and hydrocarbons emissions.) Naturally, the taxi that MOTHER's crew tested was a lot less polluting than the average American automobile, but even in perfect tune it just "squeaked by" the tests using gasoline ... registering nearly a 1-1/2% CO and a 200 parts per million HC exhaust content (both just under the legal limit).

With alcohol fuel, however, the test results improved enormously. Even with all pollution controls removed from the engine (except for the PCV valve), the cab registered a mere 0.08% CO and only 25 PPM of HC ... the equivalent of 95% less CO and 87.5% less HC, or a total of about 92% cleaner!


As we all know (some of us from experience), water and gasoline don't mix. The gasoline tends to float to the top of the mixture, leaving the water to settle below it. In a car's fuel tank, this can be disastrous, particularly during the winter season.

Alcohol, however, mixes quite well with water: The water particles distribute evenly within the mixture. As a result, not only is the winter freezing problem solved, but pure alcohol is not necessary for fuel purposes. This is very important to the small-scale alcohol fuel producer, since nonindustrial stills are generally not capable of producing more than 192-proof (96% pure) alcohol.

As far as its use in an engine is concerned, MOTHER's researchers have had excellent results with various strengths of alcohol, from 160 proof to anhydrous (200 proof). Additional water added beyond the 20% limit causes the engine to hesitate and idle roughly ... hence that practice is not recommended. As an extra benefit, the water in the fuel helps cleanse and "lubricate" the internal parts of the engine, including the valve seats, piston head surfaces, and combustion chamber.


The fuel economy of an engine is directly proportional to how rich the air/fuel mixture is ... and that, of course, is dependent upon how large the main jet in the carburetor is. Alcohol requires a richer air/fuel mix than does gasoline (9-to-1 as opposed to 15-to-1), but that difference is not reflected proportionately with respect to economy ... partially due to the fact that alcohol has a higher "octane" rating and can be utilized more efficiently.

By experimenting with orifice sizes (diameters) of the carburetor's main jet, it is possible to reach a happy medium between power and economy in a standard auto engine using alcohol. Referring to the "Economy" chart that follows, you'll see that a 40% increase in diameter over the standard jet size in MOTHER's truck resulted in a loss of only 12% of the total fuel economy ... as compared to burning gasoline and using the standard jet (the truck was fully loaded in both cases).

With a step-by-step decrease in jet size - down to 19% larger than the original - only about 5% was lost when compared with the unloaded truck using gasoline and its normal jetting. When that test was made comparing both fuels in the fully loaded vehicle, the alcohol-powered version actually showed an increase in mileage ... by a whopping 16%. This is because an alcohol-powered vehicle - partly as a result of the fuel's high "octane" rating - will maintain its economy even under extreme loads, unlike most gasoline-powered cars. The figures given above were recorded when MOTHER's 1/2-ton pickup was pulling over 2,200 pounds ... and only improved slightly when the load was removed. In comparison, when the weight was removed from the truck in its gasoline mode, mileage improved substantially ... as indicated in the chart.

It should also be noted that an increase in engine compression ratio will improve alcohol mileage considerably ... to the point where loaded or unloaded, any vehicle should equal or better its gasoline fuel mileage.


An engine powered by alcohol - if converted correctly - will have performance equivalent to, if not greater than, the same powerplant burning gasoline. This is because of the fact that alcohol has a higher "octane" rating (hence the timing can be advanced slightly), and it can stand much greater compression ratios.

Even without changing the compression ratio, an alcohol-powered engine with fairly low compression (MOTHER's pickup has a ratio of 8.5-to-1) still holds its own against its gasoline-burning counterpart. And, if the timing is advanced safely short of the "knock" limit, the torque range is broadened considerably, allowing the vehicle to pull under load exceptionally well ... in fact, it does much better under such conditions than the gasoline version does!

Mother Earth Alcohol Fuel

Chapter 1
Introduction to a Farmer's Fuel ... Alcohol
Introductory Overview of the Alcohol Production Flow Chart
A Short But Complex Story About Enzymes and Their Functions

Chapter 2
Farm Crops for Alcohol Fuel
Raw Materials
More on Raw Materials
Feedstock Handling and Storage

Chapter 3
Basic Steps in the Production of Ethyl Alcohol
More On Conversion and Fermentation
Fermentation Addendum
Alcohol Yield

Chapter 4
Control of Infection by Planned Sanitation in the Production of Fuel or Gasohol Alcohol

Chapter 5
MOTHER's Mash Recipes for Alcohol Production
Important! Read Before Making Mash
Preparing a Mash From Saccharide-rich Materials
A Handy Hydrometer Jacket

Chapter 6
Distiller's Feeds
By-product Utilization
Animal Feed By-product
More Information On By-product Utilization

Chapter 7
How the Distillation Process Works
Packed Column
Perforated Plate
Bubble Cap Plate
Solar Stills
The Reasoning Behind MOTHER's Still Design
Still Operation
Making Your First "Run"
"Economizing" Your Alcohol Production

Chapter 8
Six-Inch Column Still Plans
Three-Inch Column Still Plans
Bill of Materials

Chapter 9
Two Low-cost Backyard Stills

Alcohol as an Engine Fuel

How To Adapt Your Automobile Engine For Ethyl Alcohol Use

Ron Novak's Do-It-Yourself Water Injection System

MOTHER's Waste Oil Heater

Biofuels Library
Biofuels supplies and suppliers

Make your own biodiesel
Mike Pelly's recipe
Two-stage biodiesel process
FOOLPROOF biodiesel process
Biodiesel processors
Biodiesel in Hong Kong
Nitrogen Oxide emissions
Biodiesel resources on the Web
Do diesels have a future?
Vegetable oil yields and characteristics
Biodiesel and your vehicle
Food or fuel?
Straight vegetable oil as diesel fuel

Ethanol resources on the Web
Is ethanol energy-efficient?

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