RESEARCH AND EDUCATION TO PROMOTE CONVERSION
                                                        TO SUSTAINABLE ENERGY

               Document #3
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                                    Biodiesel vs Vegetable Oil

                                          Which Way to Go?


         With the growing popularity of Biodiesel and vegetable oil as sustainable fuels for diesel engine powered vehicles, the question often arises as to the relative merits of each fuel   In simplified terms, to run on Biodiesel, the fuel (vegetable oil) must be modified, and to run on straight vegetable oil (SVO), the engine and fuel system must be modified.  In either case, the objective is to lower the viscosity of the vegetable oil to close to that of conventional petroleum diesel fuel, in order that the fuel injection system can properly perform its function.  Biodiesel lowers the viscosity through a chemical modification of the vegetable oil, while the SVO system lowers the viscosity by heating the vegetable oil. 

         Biodiesel is a very strong solvent and with older vehicles, it can dissolve rubberized components such as fuel lines and injector pump o-rings and gaskets.  With newer vehicles, these components are often synthetics which are much more resistant to Biodiesel.  However, Biodiesel vendors often recommend blending Biodiesel with petroleum fuel in order to lessen this adverse effect, while still offering the advantages of Biodiesel such as good lubricating qualities (lubricity), lowered soot emissions, a much more agreeable exhaust odor, and sustainability.  A typical Biodiesel blend is B20, meaning that the blended product is 20% Biodiesel and 80% petroleum diesel.  Purists dislike the fact that for B20, 80% of their fuel is still petroleum based.  This tends to favor the use of vegetable oil, which does not adversely affect the rubberized components and therefore does not require blending for this purpose.  However, in cold weather, it is necessary to blend some petroleum Diesel (or Biodiesel) with the SVO or else the SVO can clog fuel filters, or even solidify at low enough temperatures. 

         SVO which meets specification should never cause a problem with an engine and fuel system that has been properly modified.  However, it is possible to use the same such oil, and by improperly processing it, produce Biodiesel that causes problems.  If, for example, the glycerin produced in the Biodiesel manufacturing process is not allowed to adequately precipitate, fuel filter clogging can result.  For Biodiesel, there is this added risk that is not present if using SVO.

         From a cost standpoint, it is self evident that if one starts with a vegetable oil that is otherwise useable in an SVO converted vehicle, and then goes through the modification process to make Biodiesel, then the Biodiesel cost is going to be higher than the SVO cost.  Some argue that if starting with waste vegetable oil (WVO), then the cost to filter, remove water or other contaminants, and bring the WVO up to specification is almost as much as the cost of converting the WVO to Biodiesel.  However, if the acceptance of these fuels is going to become anything close to mainstream, then the supply of WVO will be quickly absorbed and it will be necessary to rely primarily on virgin vegetable oil to supply the need, and so the cost of SVO should be less than that of Biodiesel.   

         The availability of the fuel is certainly a concern.  Biodiesel outlets are relatively few and far between and generally have restricted hours of operation.  Vegetable oil is available at virtually every supermarket and convenience store, many of which are open 24/7, and at warehouse outlets such as Costco.  While the supermarket or convenience store price is quite high relative to that of petroleum diesel fuel, the wide availability of SVO is certainly a plus.  Of course a Biodiesel or SVO user can always stoop to the level of just purchasing petroleum diesel, but for the average avid user of sustainable fuels, this is certainly an alternative of last resort.

         The cost to convert a vehicle to SVO can vary greatly, but once done, there are certainly advantages to using SVO.  On the other hand, the simplicity of using Biodiesel is compelling.  It is hoped that vendors of Biodiesel and vegetable oil would see these two fuels as complementary rather than competitive, and that there is an advantage for such vendors to offer both fuels.  Innovations such as a home delivery system could go a long way towards solving the availability issue for both fuels.  If prices can be kept even close to competitive with petroleum diesel fuel, the altruistic motivation of many people to “do the right thing” could create a very large market. 


© 2004 Bruce  Colley.  All rights reserved.          

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Last modified: 05/24/05

© 2003 Sustainable Energy Project.  All rights reserved