Biodiesel fuels

Biodiesel is a diesel fuel substitute usually made from vegetable oils such as corn oil, canola oil, rapeseed oil and soy oil. It can also be produced by algae or organic waste. Biodiesel has a number of advantages over conventional diesel fuel.  It sulfur free and produces lower levels of hydrocarbons than conventional diesel when burned.  Above all it is a fuel that can be produced from renewable resources.

Like ethanol biodiesel is a secondary fuel source in that it takes energy to make it.  Unlike ethanol, however, biodiesel has far greater net efficiency.  The efficiency varies depending upon what type of vegetable is used to produce it.  Soy oil has an efficiency of about 3.2 and canola or rapeseed oil have an efficiency around 4.3.  What this means is that for every unit of energy used in manufacturing biodiesel from soy oil, for example, you get 3.2 units of energy out of it. Compare this to ethanol where the net energy efficiency is only about 1.34 and you can see that biodiesel is a very viable energy alternative.

Biodiesel fuel can be combined with ordinary diesel in different blends. This is often necessary, particularly in colder climates, because soy biodiesel gels at around 32 degrees Fahrenheit. By mixing the biodiesel with conventional diesel, it can operate at lower temperatures. When used as a car fuel most studies indicate biodiesel provides equal performance to traditional diesel oil. If used in older diesels biodiesel should probably be progressively introduced.  The reason for this is that it acts more like a solvent then conventional diesel gasoline and can free up clumps of accumulated oil sludge that can potential block your fuel lines.  By introducing it progressively, moving from a light blend (5% biodiesel to 95% diesel) to a heavier blend this problem can be avoided.

The first step in making commercial biodiesel is to mix methanol (methyl alcohol) with sodium hydroxide or lye.  This results in a chemical called sodium methoxide.  This substance in turn is mixed with vegetable oil where it reacts in a process called transesterification. Under this process the glycerin in the vegetable oil is separated out leaving usable biodiesel.  Biodiesel can be burned in most compression-ignition diesel engines without any modification.

One of the challenges for most people is that biodiesel is not available in most locations.  Also, because of production costs biodiesel costs more than conventional petroleum based diesel fuel.  As oil prices rise and biodiesel manufacturing increases this differential may be reduced.  Biodiesel has not received the same commercial attention or high levels of government subsidization that ethanol has. Also, because biodiesel is usually made from crops such as corn or soy it too is caught up in the food versus fuel controversy surrounding other bio fuels such as ethanol.

Vegetable Oil Kits

A number of enterprising individuals have discovered that the vegetable oil used to today in restaurants and fast food chains can be used directly in a diesel engine if it is properly modified.  In this way it provides an environmental service by using a fuel that otherwise would be wasted and poured into landfills.  It should be noted that leftover vegetable oil is not an inconsequential source of energy.  Some experts estimate that U.S. restaurants and fast-food chains produce as much as 3 billion gallons of used vegetable oil each year. There are a number of kits on the market that allow someone to modify their car to directly use vegetable oil.

A typical conversion kit will have the following components:

1. vegetable oil tank - The tank holds the vegetable oil used for fuel separate from the regular diesel tank already in the car
2. filter - the filter is designed to remove any impurities that might be in the vegetable oil
3. tubing - the tubes connect the vegetable oil tank to the combustion chambers in the diesel engine
4. valves - this controls the flow of vegetable oil
5. switches - usually mounted on the dashboard which can be used to control the valves and therefore the flow of vegetable oil to the engine
6. pre-heater - the pre-heater heats the vegetable oil so that it can flow to the combustion chamber

Vegetable oil is much thicker than diesel oil and so, as noted above, it needs to be heated to 165 degrees or higher in order to thin it out enough to use. Consequently most vegetable oil conversion kits provide some type of vegetable oil pre-heater to thin the oil out so the engine can be started. There are two approaches that are commonly taken to heating the oil.  One approach is to use an electric heater to heat the oil.  Another approach is to run the engine for a while on conventional diesel fuel, and then use the heat from the engine to heat the oil using heat exchangers.

Because of the need to pre-heat the vegetable oil the car must usually be run for about five minutes before you can throw the switch to have it begin using the vegetable oil. The switch triggers a valve which opens the flow of vegetable oil from the now heated tank and cuts off the flow of fuel from the standard diesel tank. This process must then be reversed when you shut the engine down.  Five minutes before you turn the engine off you will need to turn the switch back to conventional diesel so that the fuel lines are purged of any vegetable oil which could condense and clog the engine. 

Vegetable oil kits have some definite disadvantages.  First, one most own a car with a diesel engine. Only about 3.6% of the cars in the U.S. use diesel engines.  Second you need to establish a source for getting your vegetable oil.  This is probably much less of an issue for most Americans since fast food restaurants that use them are just about everywhere.  Third, there is the expense of the conversion kit. The kits run between $800 and $1600 in most locations.  If you are not mechanically inclined it is likely that most good mechanics could put them in for you but that will add further cost.  Finally, there is the issue just described of having to deal with switching fuels when starting and stopping your car.  If you have the kind of lifestyle where you are doing quick short trips with your car then this requirement may be a bit more than you want to deal with.

On the other hand vegetable oil cars can for some people prove to be an ideal alternative.  It uses a fuel that is completely renewable and which could help support our agricultural economy.  The fuel is likely to be extremely cheap, possible even free if you have a good relationship with your local fast food owner.  The engine uses fuel that would have otherwise gone into a polluting landfill and it produces less hydrocarbons than conventional diesel fuel. These are not insignificant advantages in an era of global warming and high fuel prices.