Biodiesel Basics
Right about now you might be asking: Just what the heck is biodiesel, anyway? Back in Diesel's day their bio-fuel was pretty much straight vegetable oil but now we (well…not me, but you know what I mean) have the ability to create from biological sources a petro-diesel equivalent that can be used to power an unmodified diesel engine. Modern biodiesel is generally distilled from one of several types of vegetable oil and the most important element of that distillation process is known as transesterification.
Yes, I have to agree that it's a weird word but, basically (very basically), transesterification is a chemical reaction resulting in the separation of methyl or ethyl esters from glycerol; the esters can then be further refined into the final biodiesel product.
Biodiesel Drawbacks
Even though biodiesel is the theoretical equivalent to petrodiesel; there are a few major differences. For example:
- Gel Temp: The temperature at which pure biodiesel (B100) begins to gel depends largely on the type of oil from which it was distilled but biodiesel gel temps can be as high as 32°F.
- Cetane Rating: The cetane number of diesel fuel is an indication of how easily it will ignite under compression (as opposed to gasoline's octane rating which is an indication of its resistance to ignition under compression). No. 2 diesel fuel usually has a cetane rating between 45 and 50 while biodiesel ranges between 50 and 60. High cetane fuel might result in incomplete combustion and smoke if the fuel ignites too soon - not allowing enough time for the fuel to mix with air for complete combustion.
- Energy Levels: One BTU (British Thermal Unit), a common measure of energy, is defined as the amount of heat required to raise the temperature of one pound of water from 60° to 61°F at a constant pressure of one atmosphere. A study done by the University of North Dakota indicated that, while there are some significant fluctuations, #2 diesel contains about 140,000 BTUs per gallon while pure biodiesel (B100) contains about 130,000 BTUs (roughly the same as #1 diesel).
- Higher Nitrogen Oxide Emissions: Since biodiesel contains no nitrogen, the increase in NOx emissions is probably due to the higher cetane rating and the high oxygen content of biodiesel. These two qualities are generally thought to cause the nitrogen contained in the air to be converted into NOx during combustion.
- Solvent Properties: Because biodiesel acts as a solvent it's likely, when used in an engine previously powered by petrodiesel, that any sediment in the fuel system will be washed into the filters and fuel injectors. Rubber gaskets and hoses will also degrade at a higher rate. This means that filters will need to be changed within 1000 miles of changing to a biodiesel blend and the hoses and gaskets will eventually need to be changed to something that doesn't react to biodiesel; like Viton.
After reading all the preceding points concerning the differences between biodiesel and petrodiesel, which are definite disadvantages, you might be wondering why in the world anyone would ever want to use this stuff in a truck. Believe me, there is a way. Just stick with me a little bit longer and I'll try to make the case. Read Part Three: Blends & Conclusions.
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|Biodiesel: Diesel Fuel From Farmers | Part 2: Basics & Drawbacks | Part 3: Blends & Conclusions |
