Apr
7
The Difference Is and It Matters Because of the Money
April 7, 2008 | Leave a Comment
Petroleum based fuel is often thought to be on the way out. Alcohol based fuel is often thought to be on the way in. Actually, they are nearly the same molecules with one very important difference. There is oxygen in alcohol. Before the conclusions jump, the oxygen doesn’t combust when alcohols are ignited, but it sure fans the flame as oxygenation takes place during a burn.
Petroleum on the other hand is more dense as there isn’t any oxygen displacing any volume. It is also more malleable as the molecules get larger. An alcohol at the energy density of the middle distillates like diesel is too viscous or thick to be handled accurately and is sensitive to temperature making the viscosity thicker at temperatures we would need them to work. Petroleum like diesel, and even the biodiesel products are more amenable to temperature variations.
At the lightest point of one carbon atom, there is methane, add oxygen and you have methanol. Wonderful stuff, both of them, methane at working temperatures is a gas and methanol (prevented from evaporating) a liquid. Both offer great opportunities when applied properly. Next are the two carbon molecules as with petroleum ethane and ethanol alcohol. At this level, the ethanol alcohol is a useful liquid fuel that enjoys a good density. Ethane is used in the chemical industry as a feedstock and appears in some natural gas feeds.
At three carbon atom molecules, we have liquid petroleum gas or propane. It’s easily compressed to a liquid and is easily handled and comparatively safe with sensible precautions. We see propanol as isopropyl in rubbing alcohol, a cleaning solvent and as a fuel system deicer. They are common chemicals we use regularly.
When we get to four carbon atoms, it gets very interesting. The petroleum molecule is called butane, the stuff in a pocket lighter. Very low pressures are needed to liquefy it and butane evaporates slowly enough that carrying it in your pocket is very low risk, and ignites with a simple spark. The alcohol butanol is a liquid that has a lower evaporation rate than the lighter alcohols, is nearly equal to gasoline in energy density and will mix both with gasoline or diesel as a fuel extender/replacement or as an emission aid as it brings that oxygen with it, too.
The big player is that oxygen in the molecule. The downside is it adds mass, it makes alcohols vulnerable to temperature effects that limit the parameters of use. The lightest, methanol and ethanol are corrosive due to the oxygen, evaporate at high rates, and are more difficult to contain making the danger in handling and storage higher. But, both work well as racing fuels where high resistance to igniting coupled to rapid oxidation when burning make for serious opportunities for making power in internal combustion engines. As additives to higher density fuels, they offer many advantages.
Oxygen in the alcohol molecule offers another trait. The oxygen allows microorganisms the door to consume the carbon and hydrogen thus they are biodegradable. On the other hand, petroleum products are closed up and require other inputs to crack them open for plant life to make use of them as food. For the three lightest alcohols the ability to mix with water is a result of the presence of the oxygen. That oxygen door and water interactivity is the key to bioactivity for quick degradation.
All this matters because we will be increasingly going to more mixed fuel products. The sources of fuel are going to grow from just petroleum gasoline splash mixed with ethanol to include both alcohols and synthetic plus bio gasoline, diesel and jet fuel. At this writing, certain manufacturers offer “flexible fuel” vehicles that can handle a wide range of ethanol to gasoline ratios. We have to understand that is useful, but as we move on the probability that better priced mixes will come. A fuel mixed from part gasoline, butanol and ethanol may well need further adaptability in engine management and fuel controls if fed to internal combustion engines. In this future the higher the energy density, the more resistance to ignition and the most furious oxidation offers the best power output efficiency. Higher compressions will be very worthwhile and fuel mixes can be made that may be lower cost, too.
Opposed to this and where the best opportunity lies for efficiency is in external combustion engines. Farther out in the future may be “engines” that drive electric generator sets in personal vehicles and trucks. A flame burning in an engine that uses the heat can be much more efficient than limiting the energy use to the pressure of the expanding gases from the heat released alone.
Alcohol as a fuel is about played out at four carbon atoms per molecule. At five carbon atoms and higher alcohols are getting really thick and hard to work with. Butanol is the next and probably the last alcohol that may see large market share if production can be made at commercial volumes. When that happens a major shift in mixed fuel products can occur.
That makes it important to look for mixed fuel capability in the world’s personal vehicle choices. For long term value a vehicle than will run happily on a wide range of fuel densities will be worth more longer and be less expensive to drive.
It will matter, all four alcohols, gasoline, diesel, jet and the bio and synthetics are coming and nothing will stop the mixing of these into fuel products.
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