BIOFUELS

LIQUID BIOFUEL PRODUCTION

LIQUID HYDROCARBON FUELS:
One of the main problems facing man is long term supply of liquid hydrocarbon fuels. Liquid hydrocarbon fuels provide a high energy density that is essential for long distance transportation (eg. aircraft), portable power tools (eg. chain saws) and remote and emergency standby energy supply applications (eg. portable generators). However, the cost of liquid hydrocarbon fossil fuels is rapidly increasing due to: resource depletion, increasing cost of production and taxes intended to discourage use of fossil fuels that increase the atmospheric greenhouse gas concentration.

In the USA there is a movement to convert plentiful coal into liquid fuels. However, that movement is a huge mistake because the consequent CO2 emissions to the atmosphere will cause many billions of dollars in climate related damage in the USA alone and will almost certainly provoke armed conflict with many other countries. Instead the US industrial capacity should be directed toward displacing fossil fuels with electricity and with more efficiently produced liquid biofuels.

LIQUID BIOFUELS:
In urban applications liquid fossil fuels can usually be displaced by electricity obtained from nuclear and renewable energy. However, in long distance transportation applications and in portable and remote applications the appropriate replacement measure is to replace liquid hydrocarbon fossil fuels with liquid hydrocarbon biofuels. Liquid biofuel production should use non-fossil fuel energy to convert biomass and water into a high energy density liquid hydrocarbon such as butanol without net emission of greenhouse gases.

Present industrial biofuel production processes sacrifice more than half of the carbon contained in the biomass feedstock to convert carbohydrates into alcohols or light oils. This sacrifice is made because biomass is still relatively inexpensive, in part due to government agricultural subsidies. However, in the future the limited supply of biocarbon will make full utilization of the available biocarbon more important. Hence the conversion of carbohydrates into liquid biofuel should use electrolysis rather than carbon sacrifice to supply the energy required to convert carbohydrate into an alcohol or oil.

Liquid biofuels are not prime energy sources because production of a liquid biofuel requires an amount of prime energy in excess of the energy contained in the liquid biofuel.

One of the significant cost components of liquid biofuel production is transportation of biomass from the location where it is grown to the location where it is converted into a liquid biofuel. In order to make liquid biofuel production economic distributed nuclear heat sources are required to provide steam heat for biofuel production on major farms.

MICRO FUSION:
The main projected application of Micro Fusion is supply of distributed base load heat for on-farm production of liquid biofuels without combustion of fossil carbon, without burning biomass feedstock and without depleting farm soil.

NITROGEN FERTILIZER:
Sustainable large scale biofuel production requires ongoing replenishment of soil nitrogen via fertilization. Production of the nitrogen fertilizer requires production of ammonia. Production of ammonia requires energy, heat and hydrogen. Energy can come from wind, hydro-electric power or a nuclear reactor. Heat of the required temperature can come from a sodium cooled nuclear reactor. Hydrogen can come from electrolysis of water or from the thermally driven copper chloride process that is presently under development at the University of Ontario Institute of Technology (UOIT). This process also requires heat at a temperature consistent with use of a soduim cooled nuclear reactor.

PHOSPHORUS FERTILIZER:
Sustainable large scale biofuel production requires ongoing replenishment of soil phosphorus.which is a key component of plant cell walls. The phosphorus is a waste product leftover from the biofuel production process. However, it has to be physically transported and injected back into the soil to sustain large scale biomass production.

SUNLIGHT AND FRESH WATER:
Large scale biomass production is limited by simultaneous availability of both sunlight and fresh water. Lack of either prevents natural formation of biomass carbohydrate.

PRACTICAL BIOFUELS:
Practical liquid biofuels include alcohols (ethanol and butanol) and oils (biodiesel) that are produced using plant biomass as the only carbon containing feedstock. Ethanol and biodiesel have the advantage that they are simple to make. However, butanol has physical and chemical properties that are important for displacement of liquid fossil fuels in transportation and remote energy supply applications. Total liquid biofuel production is limited by the amount of carbon contained in the biomass feedstock less carbon loss via CO2 emissions from the biofuel production process and carbon loss via biomass feedstock residue.

In tropical countries such as Brazil ethanol is produced using only sunlight as a source of prime energy. However in Canada the average sunlight is not sufficient to be the sole source of prime energy for large scale liquid biofuel production. Additional prime energy from other sources is required.

FUEL ALCOHOLS:
Pure butanol (C4H9OH) and E85 (nominally 85% ethanol (C2H5OH), 15% gasoline), can both be used as substitutes for gasoline in internal combustion engines that are fitted with suitable fuel systems. However, in the winter E85 may actually be 70% ethanol and 30% gasoline in order to provide reliable spark ignition starting at low temperatures. Butanol can be used at 100% concentration year round.

Butanol has about a 25% higher energy density than ethanol and is not miscible with water. These two properties give butanol a major advantage over ethanol in practical transportation, rural heating and standby electricity generation applications. Hence this web page focuses primarily on production of bio-butanol.

Advantages of butanol over ethanol are:
1. Higher energy density;
2. Non-corrosive to steel pipes and steel storage tanks;
3. Compatible with aluminum fuel system components;
4. Does not need to be mixed with fossil fuels for use in spark ignition engines;
5. Not suitable for human consumption.

Disadvantages of pure butanol as compared to pure ethanol are:
1. Not suitable for use in high compression (diesel) engines.

In order to understand the role of Micro Fusion in bio-butanol production it is essential to understand how agricultural butanol is produced.

AGRICULTURAL BUTANOL PRODUCTION PROCESS:
The main steps in agricultural butanol production are as follows:
1. A plant feedstock (biomass) is grown that contains a high percentage of starch, sugar and/or cellulose. Ideally the biomass is highly uniform and has a relatively low water content.
2. The biomass is mechanically harvested and is transported to a nearby butanol production facility.
3. The biomass is mechanically chopped and then ground into small pieces.
4. The chopped biomass is loaded into a sealable tank and is compressed.
5. Sufficient hot water is added to completely exclude air and other gases.
6. A high temperature (~120 degrees C) aqueous chemical treatment is used to further fracture the biomass, to partially convert cellulose into glucose, to remove the lignin and to kill unwanted micro-organisms.
7. The hot water is cooled to about 35 degrees C. Heat is recovered for use elsewhere in the process.
8. The biomass is biochemically converted into the sugar glucose;
9. CaCO3 in water is added to absorb CO2. The temperature is again increased to 100 degrees C to sterilize the tank and its contents.
10. The hot water is cooled to about 35 degrees C. Heat is recovered for use elsewhere in the process.
11. Laboratory cultured micro organisms are added that ferment the sugar solution into butanol via a two step continuous extraction process. During the fermentation approximately half the mass of sugar is converted into carbon dioxide. This carbon dioxide is absorbed by the CaCO3 which converts to water soluble Ca(HCO3)2. The fermentation tank may be kept under metnane (CH4) pressure to block biochemical pathways that yield methane (CH4). The choice of cultured micro organism and operating temperature affects the butanol yield because the various sugar isomers behave differently, depending upon the micro organism and the temperature. It is important to not produce ethanol and acetone as production of these chemicals will cause the butanol output to decrease.
12. Practical butanol production requires two bichemical reaction vessels, one to produce butyric acid and the other to convert the butyric acid into butanol.
13. When the butanol concentration exceeds 9% the butanol solution is saturated and additional butanol tends to float on top of the process water. As butanol is produced it is continuously decanted off the top of the second step reactor vessel.
14. The butanol that is decanted off contains some water. The butanol is concentrated using a distillation/membrane diffusion process known as pervaporation and/or a molecular sieve. In order to make fuel alcohol it is necessary to concentrate the alcohol to about 99.5% by removing almost all the water.
15. The residue biomass may contain a high fraction of cellulose. This cellulose can be broken down into sugar using high temperature steam, superheated water or micro-organisms similar to those in the stomach of a cow. This sugar is fed back into the process at step #8.
16. The carbon dioxide that was emitted during the fermentation process is released from the Ca(HCO3)2 by heating the Ca(HCO3)2 solution to about 90 degrees C in a tank that is vented to the atmosphere. The left over CaCO3 will form scale in this tank. In a closed agricultural system such as an algae facility the vented carbon dioxide can be recycled to enhance carbohydrate formation.
17. In order to minimize transportation costs the butanol should be produced close to the location where the plant carbohydrate is grown.
18. The remaining biomass residue can be broken down by pyrolysis to release methane (CH4). The methane is used in efficient convertion of butyric acid to butanol. This pyrolysis process also prevents natural decay of the feedstock residue releasing methane to the atmosphere.
19. The resulting carbon residue contains a large fraction of phosphorus. This residue should be reburied as a soil fertilizer and remediation agent.
20. The butanol production process requires heat. The amount of this heat is comparable to the chemical energy contained in the resulting butanol. If the required heat is obtained by combustion of fossil fuels instead of a nuclear source the agricultural butanol production may cause net production of greenhouse gas.
21. The butanol production process can be greatly improved by obtaining the required heat from a Micro Fusion Unit. Then there is no release of fossil carbon dioxide or particulate matter to the atmosphere. Since the Micro Fusion unit can be located on or adjacent to a major farm, farmers are able to minimize their transportation costs and can easily bury feedstock residue, thus returning phosphorus and trace fertilizing elements to the soil to prevent soil depletion.
22. Typically an ammonia based fertilizer is used to replace soil nitrogen. The ammonia is produced at a central facility using energy derived from a nuclear power plant.

Step #1 requires energy for plowing, seeding and crop irrigation;
Step #2 requires energy for harvesting the carbohydrate feedstock;
Step #3 requires energy for chopping the carbohydrate feedstock;
Step #4 requires energy for loading and compressing the feedstock;
Steps #5 and #6 require heat;
Step #7 recovers some heat;
Steps #8 requires little heat or energy;
Step #9 requires heat;
Step #10 recovers heat;
Steps #11, #12 and #13 require no heat or energy;
Step #14 requires heat;
Step #15 requires more heat;
Step #16 requires heat;
Step #17 requires no heat;
Step #18 requires heat:
Step #19 requires energy for carbon residue distribution and reburial;
Steps #20 and #21 are comments that involve no additional energy or heat;
Step #22 requires heat and energy for producing ammonia.
Thus the cost of liquid butanol produced without reliance on fossil fuels is strongly dependent on the costs of electricity and nuclear heat.

BIOFUEL FEEDSTOCK:
Growing plants use sunlight to combine water (H2O) and carbon dioxide (CO2) to form a class of chemicals known as carbohydrates. Common carbohydrates are isomers of C6H12O6 (starch and six carbon sugars), isomers of C5H10O5 (five carbon sugars) and cellulose (C6H10O5)n (long chain molecules). These materials have the net formation reactions:
6 CO2 + 6 H2O + sunlight = C6H12O6 (solid) + 6 O2 (gas)
5 CO2 + 5 H2O + sunlight = C5H10O5 (solid) + 5 O2 (gas)
n (6 CO2 + 5 H2O) + sunlight = (C6H10O5)n (solid) + n (6 O2) (gas)
Also present in biomass at 25% to 33% by weight is a complex phosphorus containing organic polymer known as lignin. Lignin forms plant cell walls which guide water flow, provide compressive structural strength and protect the cellulose from microbial attack.

LIGNIN:
Dry biomass is a porous low energy density solid which is not a suitable fuel for vehicles. Dry biomass is bulky and is expensive to handle and transport. Dry biomass contains significant amounts of nitrogen, phosphorus, potasium and trace elements that are chemically bound in the lignin. Lignin is the substance that forms a protective coatings around cellulose fibers. Plants take up these elements via water soluble chemical compounds contained in the soil. Agricultural biofuel production is sustainable only if there is a mechanism for returning these elements to the soil in water soluble form.

Nitrogen in the soil can be replaced via crop rotation with a nitrogen fixing plant type or via an ammonia or nitrate type fertilizer. Phosphorus, potasium and various other elements can be returned to the soil by using residue from the biofuel production process as a fertilizer.

PRETREATMENT:
Dry biomass must be chopped and ground into small pieces to expose enough surface area to obtain a satisfactory biofuel production rate. To permit biochemical processing the biomass must be sterilized to kill unwanted micro-organisms and chemically treated to remove the lignin.

DECOMPOSITION OF CARBOHYDRATES:
CARBON PRODUCTION:
If biomass is heated in water to over 180 degrees C an exothermic process known as hydrothermal carbonization takes place. The chemical reactions are:
C6H12O6 = 6 C + 6 H2O + heat
C5H10O5 = 5 C + 5 H2O + heat
(C6H10O5)n = n (6C + 5H2O) + heat
The resulting solid carbon is suitable for soil remediation but is not easily converted into a liquid fuel. Note that this process does not cause formation of a gas other than water vapor. Hence this thermal decomposition can proceed in a sealed pressure vessel if there is a process for heat removal. Onset of hydrothermal carbonization sets a practical upper limit of about 160 degrees C on the temperature used for initial aqueous processing of biofuel feedstock. This temperature limit applies to the lignin removal process. After the available plant sugars are removed from the biomass hydrothermal carbonization of the feedstock residue can be used to prevent the residue decaying to form methane and carbon dioxide.

METHANE PRODUCTION:
Carbohydrate in water can be broken down at a relatively low temperatures (30 C to 40 C) and low methane and carbon dioxide partial pressures (~0.5 bar) via anaerobic digestion using the biochemical reactions:
C6H12O6 = 3 CH4 + 3 CO2
2 C5H10O5 = 5 CH4 + 5 CO2
(C6H10O5)n + H2O = n (C6H12O6) = n (3 CH4 + 3 CO2)
The reaction products are the gases methane (CH4) and carbon dioxide (CO2). This gas mixture is easy to transport via a pipeline but, due to its low energy density, this gas mixture is unsuitable as a vehicle fuel and is unsuitable for direct injection into the North American natural gas distribution system. This anaerobic digestion process occurs in both municipal sanitary sewage treatment plants and in municipal waste land fills. To optimize liquid biofuel production it is generally necessary to prevent methane production by killing methane producing bacteria and by imposing a high partial pressure of methane. However, some methane may be required to convert acetone into butanol.

GLUCOSE PRODUCTION FROM COMPLEX SUGARS:
A chemical step that is crucial to efficient biofuel production is conversion of complex sugars into the simple sugar glucose. The net chemical reaction is:
C12H22O11 + H2O = 2 (C6H12O6)
This reaction is quite slow.

GLUCOSE PRODUCTION FROM STARCH:
A chemical step that is crucial to efficient biofuel production is conversion of the starch polymer (C6H12O6)n into the sugar glucose (C6H12O6). The net chemical reaction is:
(C6H12O6)n = n (C6H12O6)
This reaction is triggered by various enzymes.

GLUCOSE PRODUCTION FROM CELLULOSE:
A chemical step that is crucial to efficient biofuel production is conversion of cellulose into the sugar glucose. The net chemical reaction is:
(C6H10O5)n + n (H2O) = n (C6H12O6)
This process by itself is very slow. However, there is a biochemical pathway such as occurs in the stomach of a cow that can accelerate this process. It is a tandem process with some glucose decomposition that releases methane. The glucose decomposition provides the energy required to accelerate the cellulose breakdown.

ETHANOL PRODUCTION:
Carbohydrate in water can be biochemically broken down at a relatively low temperatures (30 C to 40 C), high methane pressure and low carbon dioxide pressure (< 1 bar) to form ethanol (C2H5OH) via anaerobic digestion using the reactions:
C6H12O6 = 2 C2H5OH + 2 CO2
3 C5H10O5 = 5 C2H5OH + 5 CO2
(C6H10O5)n + n (H2O) = n (C6H12O6) = n (2 C2H5OH + 2 CO2)
The first of these biochemical reactions is known as fermentation and is extensively used in the beer, wine and liquor industries. The third reaction is accomplished using proprietary organisms that have been developed specifically for cellulostic ethanol production. These biochemical reactions use about one third of the available non-lignin biocarbon to form carbon dioxide (CO2), which removes oxygen from the plant carbohydrate. Hence only two thirds of the non-lignin biocarbon is available to form ethanol. When the lignin biocarbon is considered, less than half of the feedstock biocarbon actually goes into the biofuel.

To prevent formation of methane (CH4) the anaerobic digestion should take place within a closed rigid pressure vessel that is completely filled with water, so that a high partial pressure of CH4 quickly forms. There should be sufficient powdered CaCO3 present to fully absorb the CO2 via the chemical reaction:
CaCO3 + CO2 + H2O = Ca(HCO3)2
Note that CaCO3 is insoluble in water whereas Ca(HCO3)2 is soluble in water. After the ethanol (C2H5OH) formation is complete the Ca(HCO3)2 solution can be heated to release the CO2 and convert the Ca(HCO3)2 back into CaCO3 + H2O.

ACETIC ACID PRODUCTION:
In the future, when increasing demand for biofuels leads to a shortage of plant carbohydrate feedstock, the dominant biofuel production method may be to biochemically convert plant carbohydrate into dilute acetic acid (CH3COOH) and then to electrolyse that dilute acetic acid to form ethanol.

Provided that the oxygen liberated by the electrolysis process is not permitted to contact the ethanol, acetic acid biofuel production does not form CO2 and hence maximizes the amount of biofuel produced per unit of biomass feedstock consumed. However, acetic acid biofuel production requires more non-solar energy per unit of biofuel produced than does present ethanol production. Acetic acid biofuel production may eventually become important as a dispatchable load for effectively using surplus unconstrained wind generation.

One way to break down plant carbohydrate at low temperatures (30 C to 40 C) is via the anaerobic digestion biochemical reactions:
C6H12O6 = 3 CH3COOH
2 C5H10O5 = 5 CH3COOH
(C6H10O5)n + n (H2O) = n (C6H12O6) = n (3 CH3COOH)
These reactions are favored if there are high partial pressures of both CH4 and CO2. These reactions produce dilute acetic acid (CH3COOH) aka vinegar. Note that there are no gaseous reaction products. The first of these three reactions can be realized using anaerobic bacteria of the genus Clostridium. The second and third of these reactions need additional biochemical investigation. The third reaction is important because it is energetically probable. With a suitable microbe direct conversion of cellulose to acetic acid should occur relatively quickly.

One of the problems with this anaerobic digestion methodology is that it operates only in dilute acetic acid solutions, so to enable the process the acetic acid must be removed as it is produced. The acetic acid is removed by converting it into ethanol and physically separating the ethanol (a heat intensive process).

Another issue is that converting acetic acid (CH3COOH) into ethanol (C2H5OH) requires hydrogenation by electrolysis, which is energy intensive. The oxygen released by electrolysis must be continuously extracted to prevent the oxygen reacting with the ethanol.

Note that the anaerobic digestion should take place within a closed rigid pressure vessel that is completely filled with water, so that high partial pressures of both CO2 and CH4 quickly form to prevent gas emitting carbohydrate decay processes occurring. There should not be any CaCO3 present that can reduce the CO2 partial pressure via the chemical reaction:
CaCO3 + CO2 + H2O = Ca(HCO3)2

The high CO2 and CH4 partial pressures increase the mechanical complexity of selective oxygen extraction.

HYDROGENATION:
Hydrogenation of acetic acid is performed by electrolysis of the dilute CH3COOH / water solution. In this solution part of the CH3COOH ionizes to produce CH3CO+ ions and OH- ions. Part of the water ionizes to form H3O+ ions and OH- ions. At the negative electrode the electro-chemical reaction is:
CH3CO+ + 3 H3O+ + 4 e = C2H5OH + 3 H2O
and at the positive electrode the electrochemical reaction is:
OH- + 3 OH- = O2(gas) + 2 H2O + 4 e
Note that the concentrations of CH3CO+ ions and H3O+ ions must be correct with respect to each other for the electrolytic production of ethanol to operate properly. The oxygen gas must be continuously extracted to prevent it oxidizing the ethanol. This hydrogenation step consumes a lot of electrical energy, so it is crucial that this step operates at high efficiency.

The C2H5OH is concentrated using membrane type separation equipment to minimize the amount of energy and heat required by the concentration processes. The water should be recycled to improve recovery and utilization of both C2H5OH and CH3COOH.

PRACTICAL LIMITATIONS OF FUEL ETHANOL:
Ethanol has the advantage that it is relatively easy to make but it has the disadvantage that it has a high affinity for water. Separating ethanol from water to form anhydrous ethanol (fuel ethanol) is a heat intensive process. The energy density of the resulting concentrated ethanol is about 0.66 times the energy density of gasoline. The affinity of ethanol for water (it is miscible with water) makes ethanol corrosive and incompatible with most existing petroleum pipelines, fuel handling and fuel storage equipment. In an internal combustion engine pure ethanol does not form an explosive air-fuel mixture at low temperatures. These problems weigh heavily against practical widespread use of ethanol as a liquid fuel for use in vehicles, emergency equipment and for use at remote locations.

BUTANOL PRODUCTION:
Butanol (C4H9OH) has a low affinity for water and has other desirable fuel properties similar to light oils. Butanol is an excellent liquid fuel for internal combustion engines.

In theory ethanol (C2H5OH) can be chemically dehydrated to convert it into butanol (C4H9OH) according to the net chemical reaction:
2(C2H5OH) = C4H9OH + H2O
Recently genetically enhanced micro-organisms and support techniques have been developed that convert glucose into butyric acid (C3H7COOH) and then into butanol (C4H9OH) via a two stage continuous process. The associated net biochemical reactions are believed by this author to be:
C6H12O6 = C3H7COOH + 2(CO2) + 2(H2) [1st Stage]
and
2(C3H7COOH) + CH4 = 2(C4H9OH) + CO2 [2nd Stage]
Note that carbon dioxide (CO2) must be selectively removed so that unreacted methane (CH4) can be efficiently recycled.

The first stage uses a microorganism that produces exclusively butyric acid (C3H7COOH). All other metabolic products are blocked by apparatus sterilization.

The second stage uses a well known organism to convert butyric acid into butanol (C4H9OH). The butanol floats on top of the second stage reaction vessel allowing 90% butanol to be decanted off. The addition of methane (CH4) gas to the second stage reaction vessel prevents a biochemical pathway operating that otherwise yields acetone (CH3COCH3). If this methane is not present the second stage biochemical reaction becomes:
2(C3H7COOH) = C4H9OH + CH3COCH3 + CO2
Acetone (C3COCH3) is an undesirable product for fuel purposes because it is miscible with water.

Hydrogen is available from the first stage of the butanol production process, but the cost of transporting that hydrogen to an ammonia production plant is likely prohibitive. It is probably more cost effective to use hydrogen generated during the butanol production process for local electricity generation.

YIELD:
An important aspect of butanol production is the yield where: yield = [weight of butanol (C4H9OH) produced] / [weight of dry biomass consumed].
Recall that biomass is typically 28% lignin, so only 72% of the biomass is carbohydrate that can form butanol.

Without hydrogenation the maximum possible yield of butanol is:
[(weight of butanol) / (weight of sugar)][(weight of sugar) / (weight of feedstock)]
For corn:
[(weight of sugar) / (weight of feedstock)] = .72
According to the above chemical equations:
[(weight of butanol) / (weight of sugar)]
= [2(C4H9OH) / 2(C6H12O6)]
= 2(74) / 2(180)
= .411
Hence the theoretical yield of butanol is:
= .72(.411) = .296
The claimed actual butanol yield from corn via the butyric acid butanol production process is about:
16.9 lbs / 56 lbs = .301
The small discrepency may be because the corn used had 74% starch instead of 72% starch.

Note that the methane (CH4) used in the second reaction step is assumed to come from thermal decomposition of the lignin. If this methane comes from decomposition of sugar the yield drops by a factor of:
(2 / 2.333) = (6 / 7).

The role of Micro Fusion is to provide the heat required to drive the butanol production process. In the absence of nuclear heat and externally produced electricity the biofuel fuel yield per tonne of dry biomass consumed will be much smaller.

FINANCIAL VIABILITY:
The financial viability of farming to produce biofuel is determined by:
1. The prices of liquid fuels and their substitutes;
2. Access to a market with liquid fuel vehicles and liquid fuel heating;
3. The incentives or taxes related to biofuels;
4. The cost of Micro Fusion and biofuel production equipment;
5. The competing uses that a farmer has for his land and irrigation water;
6. The cost of electricity.

BIODIESEL PRODUCTION:
Another way to break down plant carbohydrate is via a high temperature pyrolysis (anaerobic thermal decomposition) process that yields biodiesel. Biodiesel is an oil that can be used to fuel diesel engines. However, the biodiesel yield per unit mass of biofuel feedstock is relatively small.

Much research and development is being devoted to development of new microbes that can directly convert biomass into oil without thermal decomposition. A major advantage of oil over ethanol is that it is much easier to separate from water. However, oil has few advantages over butanol. If all the prime energy must come from sunlight the direct oil production paths are not economic in northern countries such as Canada where both the ambient temperature and the average sunlight are much less than in tropical countries. This author believes that in Canada once fossil oil is exhausted bio-butanol will likely be the dominant liquid fuel.

This web page last updated August 3, 2011.