Biofuel vehicle

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See also the biofuel entry, which discusses biofuels in the larger realm.


Diesel Engines

In 1900, Rudolph Diesel demonstrated his revolutionary engine design at the World's Exhibition in France. What made this demo unique was not the engine, but the fuel -- it was running on peanut oil!

Diesel was a humanitarian who deplored the dominance of steam power of the day. Steam engines were large, expensive, and relied for fuel on a coal industry that had become monopolized by a few big suppliers. Diesel wanted to liberate small businesses and farmers by allowing them to produce mechanical energy from vegetable oil.

But others soon discovered that diesel engines could run from heavier fractions of petroleum that were produced as a waste product of kerosene lamp oil(which had just displaced whale oil), and the emerging fuel gasoline. And the rest is history -- injectors and fuel pumps became optimized for the lighter fuel, and the use of vegetable oil fuel was forgotten.

Fast forward to 1970. America is awash in more cheap oil than it had ever produced. But that is the nature of bell curves; the moment before decline begins is the highest production point, and by the late 70's, America was in a panic over the permanent decline of domestic oil production, a decline that continues to this day.

By the early 80's, gas prices had skyrocket to levels not seen since, after accounting for inflation. The public demanded more efficient vehicles, and the most agile manufacturers responded with diesel engines, due to their high efficiency.

In engines to make combustion more efficent the simple solution is to increase compression, putting the extra squeaze on the fuel/air mix raises the temperature and increases the rate the fuel burns at. This leads to more energy being released and better fuel efficency. Sounds great but (seems like there's always a but) the increased pressure and temperature cause more of the nitrogen in the air (about 75% of air is nitrogen with almost all the remaining 25% being oxygen) to combine with oxygen creating Nox also known as Nitrogen Dioxide. Nox is a polutant that many people think of being associated with diesel engines but it is present in the exhaust of both gas and diesel engines, but (always that but) for gas engines catalyitic converters have been found to remove up to 95% of Nox emmisions, reasearch is ongoing for a catalyitic converter for diesel engines since the 70's and no luck yet. Running your engine on an oxygen/diesel or gas mix would eliminate Nox emisions but the energy cost of separating the oxygen from air reduces the hp from the engine and oxygen separators are expensive pieces of equiptment.

Diesel engines are efficient for two reasons:

  1. heavier fuels contain more energy per unit volume than light fuels, such as gasoline or alcohol, and
  2. higher pressures and temperatures provide more complete combustion of the fuel. This combination can result in efficiencies of 40% or more over that of gasoline engines.

Although diesel engines are known as smokey, smelly beasts, this higher efficiency actually means that they emit fewer pollutants over a given distance than gasoline engines. But the pollutants they do emit, particulates and unburnt hydrocarbons, are particularly troublesome for people with breathing difficulties.

Enter Biodiesel

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After the oil price shocks of the late 70's and early 80's, experimenters began to figure out a way to make thick vegetable oil slip through modern injectors and injection pumps that had become optimized for lighter petrodiesel. By combining alcohol with vegetable oil in the presence of an alkaline catalyst and low-grade heat, the three fatty acids in the triglycerides that make up vegetable oil split apart, and the viscosity is reduced to something similar to petrodiesel fuel. Glycerine sinks to the bottom, and can be used as a natural detergent, or for soapmaking.

Biodiesel can be used in nearly any diesel engine, without any engine conversion. However, biodiesel is a stronger solvent than petrodiesel -- so much so that it will not only "clean out" the fuel tank, sending debris into the fuel filter, but it will also soften and dissolve many rubber and plastic products, including those used in fuel lines and pumps in older vehicles.

This deterioration can take years, however, and the replacement of rubber components doesn't have to happen immediately.

Biodiesel features much lower pollution than petrodiesel, in almost all aspects. It is naturally oxygenated, which means that it burns more completely, which is particularly effective in reducing the pollutants of most concern to those with breathing problems: unburnt hydrocarbons and particulates. However, this oxygenation also results in higher combustion temperatures, which results in slightly elevated oxides of nitrogen, a component of photochemical smog.

Another big advantage is carbon dioxide emissions, which cause global climate change. Because vegetable oil comes from plants that consumed carbon dioxide last year, rather than millions of years ago, as is the case with petrodiesel, it can be described as carbon-neutral.

However, most commercial biodiesel is made with methanol, which could be made from biomass, but is currently made from natural gas, a fossil fuel, so that portion of biodiesel does produce a net increase in greenhouse gas. Also, commercial biodiesel is produced from crops that were factory-farmed using large amounts of petroleum products for farm machinery fuel, fertilizer, and insecticide.

Also, biodiesel has a slightly lower energy content than petrodiesel -- 5% to 10% lower. In typical use, this is barely noticeable, but in low powered vehicles, it makes a difference.

One other disadvantage is that biodiesel typically has a higher gel point, the temperature at which waxes begin to solidify. This results in waxing the filter, or temporarily clogging the fuel filter, at temperatures as high as a bit above freezing. This can be remedied by cutting the biodiesel with 25% to 75% petrodiesel -- at least until the temperature warms up!

Straight Vegetable Oil

Straight vegetable oil (SVO) is too thick to get through modern injection pumps and injectors without causing damage, but chemical transformation into biodiesel is not the only way to make it thinner. When heated to 80° Centigrade (180° Fahrenheit), common vegetable oils are no more viscous than cold diesel fuel.

This typically requires an extra tank and engine fuel supply modifications. By pre-heating the SVO with a combination of radiator coolant and electric heat, the SVO runs the diesel engine with no problems. The engine is started on biodiesel (or blend, if below freezing) and run until hot, then an electric valve switches the engine to the SVO tank.

The pollution from SVO is not as well studied as that of biodiesel, but it is thought to be similar to biodiesel -- and much less than petrodiesel pollution. The Danish Center for Plant Oil Technology has some interesting figures comparing rapeseed (Canola) oil and diesel fuel: 42% lower carbon monoxide, 63% lower unburned hydrocarbons, 19% lower nitrogen oxides, and 42% lower particulates.

Depending on the source of the oil, it has more or less the same energy content as petrodiesel -- more energy than biodiesel. This can be noticeable on under-powered vehicles.

Waste Vegetable Oil

SVO is more expensive than petrodiesel fuel, and the ethics of burning food for transportation must be questioned. But after it's been used to cook food, waste vegetable oil (WVO) can still be used as fuel! Restaurants typically pay "recycling" companies to take away their waste oil, which is then used in animal food or cosmetics. This is not closed-end recycling, and is non-sustainable.

While not at first obvious, using WVO as a fuel is actually closed-end recycling, since the CO2 that is emitted is sucked up by the next year's oil crops.

WVO must be "cleaned" before using. This can be as simple as days to weeks of gravity settling, or it might be pumped through filters. Using cleanable, reusable filters eliminate the waste of replaceable filters.

Because WVO is gleaned from a wide variety of sources, it's energy content and pollution is impossible to characterize accurately, but it should be similar to SVO.

Appropriate Use

SVO/WVO is certainly an most fuel for use in farm machinery. It is produced on the farm, and therefore doesn't have to be transported great distances. Most farm machinery is already diesel powered, and thus little infrastructure change is required. The simple modification can be done by anyone with basic mechanical and plumbing skills.

Some quick calculations indicate that one acre's worth of rapeseed oil may produce enough vegetable oil to provide all needed cultivation for an additional 7 to 15 acres of food crops. In addition, the rapeseed cake left after pressing the oil can be used as a natural, organic insecticide.

More Information


Ethanol is the stuff they put in drinks to make you feel woozy! It can also be used in adapted gasoline engines, which, together with subsidies to politically important farming regions, has made it a rapidly growing alternative fuel.

But the situation is not so rosy. Dr. Pimentel of Cornell University has determined that, when you count all the fuel used to produce the corn as well as the fuel used to distill the ethanol, more energy is consumed in making corn-based ethanol than is contained in the ethanol itself. It is a net energy loser!

If the byproduct of ethanol production is put to use, its production is better justified, but the production process is very hard on the byproduct, and little nutrition is left, compared to the cake left over from pressing oil for diesel engine use.

Besides politically-motivated subsidies, the main thing ethanol has going for it as a fuel is that it can be used in common gasoline engines, but it is corrosive, and will degrade components of engines that are not specifically adapted for it. Beginning in the 1984 model year, some new cars are certified for "E85", which means they are capable of running without damage on 85% ethanol, 15% gasoline.

Ethanol may be more sustainable for crops with higher sugar content. Starchy crops like corn require two trophic exchanges, from starch to sugar by bacteria, then to alcohol by yeast, and each takes energy out of the process.

Brasil is reportedly having better results with sugar cane than can be had with corn, and common "sweet crops" like apples or sugar beets could be used, but since ethanol must be distilled, the energy input is much greater than with biodiesel or SVO/WVO.

Gas Pyrolisis

During World War II, gasoline was in short supply. In many places in Europe in the latter days of the war, wood gas was widely used to power engines designed for gasoline. It was chosen because of the low infrastructure costs (needs little processing), doesn't require the burning of "food", simplicity of engine conversion and the widescale availablity of wood as fuel. In some areas of Japan, it's indiscriminate wartime use cleared the Japan and Korea countrysides of forest, an enviromental nightmare they are only recovering from now. As with all alternative energy strategies there is no magic bullet, we must always start from the perspective of what do we need, how can we reduce our use.

The liberation of the gas from the wood is is an energy intensive process. All wood has roughly 6600 btus per pound at 15% moisture and it takes about 1600 btus to gassify the wood, leaving about 5000 btus available in the wood gas. It can have a high EROEI (energy return over energy invested) but due to the nature of generation on demand systems introduces some complexity that reduces its friendliness for vehicles or devices that require large variations in power output.

Wood gas requires modifications to engines to run. Even then, the lower fuel density will reduce the engine's top performace by around 30%. Gasifiers must be made to match the expected engine loads as they have limited turndown ratios (if the gasifier is designed to produce 4 liters per minute, and it's turndown ration is 4 to 1 then it will be able to go down to 1 liter per minute but any lower will cause trouble in the quality of the gas supplied. This can make for vehicles which don't idle well.

Wood gasification is poorly understood outside of Europe and Australia, where it was used as a very important swing fuel during and after WW2. It was used then out of necessity due to oil supplies being rationed and restricted. It was the fuel of choice because of it's high energy return and it's ease of converting existing engines to straight wood gas or duel fuel vehicles. The same arguments stand today. All wood is relativly equivelent in BTU value, at 15% moisture. 1 pound of wood has the stored heat enenergy of 6,600 btu relative to mineral diesel which has about 32,000 btu or gasoline with about 30,000 btu.

To gasify wood to "producer gas" requires about 1,600 btu energy (lower if the wood is drier) this gives an after gasification btu energy of at least 5000 btus per pound. Its true that the fuel density is lower than alchool or biodiesel, but let's examine the energy input side, how much energy does it take to plough, seed, weed, harvest, dry, threash, crush, compress a field of rape to get how much oil. I would imagine you would be getting at most a couple of gallons/per acre (actually, more like 50 gallons per acre --Jan Steinman), now imagine the same acres left standing as a copice wood (sustainable technology refined by the Celtic iron makers before the Romans arrived). It is now wild animal habitat used by diverse species. Each year, you travel through cutting all trees over 2" diameter, that wood is chipped and dried, and it is now gassifier fuel. To me this seems to be the most reasonalbe "on demand" fuel.

I would say that the other biofuel which has been extensively proven is biodigestion for methane production, this uses most sucessfuly animal and human waste to create methane gas which can be directly burned, some variants use plant waste, but it is not nearly as productive. The problem with methane production is that it's difficult to store in large quantities but produced rather slowly so if you have a load like an engine or even a large oven, it may take a very large digester to make it run and when you shut off your oven you need to do something with the methane, and storing it in any kind of larger quantity, is not reasonable, so it is well suited to be sized to lighting requirements and some cooking but beyond that isn't great, unless you have a relativly constant load that can be matched to it's production.

Heating wood to high temperatures in the absence of oxygen produces hydrogen, methane and carbon monoxide as well as sometime some unfriendly tars. This is a process related to Wood Gasification called Destructive Distillation and can create useful gas, useful but toxic chemicals and methanol a wonderful liquid fuel. The main differance between the 2 processes is the oxygen free enviroment in destructive distlation, in wood gasification limited amounts of oxygen are used to burn fuel creating heat and a hot reactive mass, whereas in destructive distillation heat is used from an ouside source to heat the wood and no oxygen is added. --Drew Rokeby-Thomas


Gasoline engine technology is ubiquitous, and has caused marginal biofuel techniques to attract undeserved attention as "green fuels" when they actually hasten the demise of modern civilization through the depletion of fossil fuel. Corn-based ethanol cannot power vehicles in a sustainable, low pollution way.

Wood gassification has a very positive energy return but do to poor turndown ratio's may not be suitable for the automobiles of today. The engine modifications are more complicated than converting to biodiesel (perhaps with a much greater energy balance, but the dust hasn't settled in that debate), or converting diesel engines to SVO/WVO. A very useful fuel source but not as convinent as a fuel you can pump. Definataly a suitable for stationary engines esp those with relativly constant loads (water pumps, generators, mills,ect.

Diesel technology is currently well suited to biofuel vehicle use. But diesel vehicles are rare, and command a premium price. This is offset by their generally greater durability and longer life. In addition, older diesel engines are simple to maintain.

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