I speak often to people who are concerned for our environment and want to do the right thing when driving their car. Before purchasing a diesel vehicle ro run renewable fuels, make sure you know the difference between fuel sources and what will work best for you.
Diesel fuel is made from petroleum and is a very efficient and energy dense fuel when used in a compression ignition engine. (diesel) It takes less energy to crack petroleum into diesel fuel than it takes to make gasoline. It also burns more efficiently in a diesel engine more miles to be traveled per gallon and producing less heat.
Biodiesel is another form of diesel fuel that is made from plant oils or animal fats instead of petroleum. I run several of my personal vehicles on biodiesel including VW TDIs, a Dodge RAM and a Ford Excursion. In order to make the oils or fats close to the same consistency as diesel fuel, it is chemically modified using an alcohol as an additional reactant and a catalyst. Typically, the alcohol reactant is methanol and the catalyst is Sodium Hydroxide or Potassium Hydroxide.
The oil is heated to facilitate the reaction. The alcohol and catalyst are mixed together and mixed into the oil causing a chemical reaction called transesterification. Transesterification creates biodiesel fuel and a waste product called glycerine. After the reaction, the glycerine separates from the biodiesel and drops to the bottom of the reaction vessel. The biodiesel is removed, washed and dried before using it in a vehicle as fuel.
Biodiesel is used in several different ways and there is a naming system to identify its type. In its purest form, biodiesel can be used without dilution direct in a diesel engine. When it is used as 100% biodiesel with no diesel mixed in, it is called B100. (‘B’ for Biodiesel and ‘100’ for 100%) The more common way to use biodiesel is to dilute it with diesel fuel in several different ratios. B20 is a mixture of 20% biodiesel and 80% diesel. B50 is a mixture of 50% biodiesel and 50% diesel.
Diesel Fuel Additive
When the dilution of biodiesel drops below 10% it is usually considered to be a fuel additive similar to the way ethanol is used as a 5% additive in gasoline. B5 is the most commonly used dilution for a diesel fuel additive. 5% biodiesel and 95% diesel.
Waste Vegetable Oil
Waste Vegetable Oil or WVO can be used directly in a diesel engine by using heat to reduce the viscosity of the oil to make it closer to the consistency of diesel fuel. (Straight Vegetable Oil (SVO) can also be used in the same method described here. It is just unused vegetable oil so it is not a waste-stream-based product) Reducing the consistency allows it to flow in the fuel lines and combust properly in a diesel engine. For this to work, the fuel system on the diesel vehicle must be modified to heat the oil before combustion. Typically, WVO at temperatures of approximately 160 degrees Fahrenheit is the same consistency as diesel fuel. I have personally run a Ford Ranger and a Mercedes on two tank WVO fuel systems.
Systems either use waste heat from the the engine to heat the fuel or an electric heater run off of the electrical system in the vehicle. In the case of the waste engine heat system, the vehicle is started on regular diesel and then switched to WVO once the vehicle is up to operating temperature. (typically 180-210 degrees Fahrenheit)
Two Tank Systems
The system described above for heating the fuel is typically used with a separate tank for diesel fuel and another tank for WVO. A switch mechanism is used to change the tank source once the vehicle is at operating temperature or the electric heat source has heated the fuel to the proper temperature.
One Tank Systems
There is a practice that some drivers use that leverages a one-tank system for WVO. Instead of relying solely on heat to reduce the viscosity of the oil, they mix it with diesel and/or regular unleaded gasoline (RUG) to thin out the oil. They pour the mixture into the single stock tank of the vehicle and run it in this manner. The one-tank method can be problematic in colder weather and since proper dilution of the oil can be difficult to maintain if the fuel is blended in the tank itself.
I hope this helps you with understanding the differences in the types of diesel fuel