Diesel engines were originally designed and build by Rudolf Diesel, a German mechanical engineer, in 1892. Standard combustion engines mix combustible fuel such as gasoline or ethanol with air in a confined space and ignite the mixture with a spark. The fuel/air mixture burns and expands, creating pressure against the walls of the confined space. In an engine, one of the walls of the space is the top of a piston. The movement of this piston from the expanding gases is what propels a vehicle down the road. A diesel engine is not too much different from a gas engine, fuel is still mixed with air, the fuel/air mixture still burns, expansion of the burn generates motion for the vehicle, the one difference is how the fuel/air mixture starts burning. In a gasoline engine the fuel/air is ignited with a spark, in a diesel engine air is compressed to which generates heat of over 500 degrees C, once the air is compressed diesel fuel is injected into the space and begins to burn. Since the fuel in the diesel engine just needs to burn at high temperatures and not explode with a spark it is reasonable to think that a diesel engine can run on many different kinds of fuel, this is true and in fact the original diesel engine from 1892 ran on peanut oil.
Now, the properties of the diesel engine haven’t changed much since 1892 and it is still possible to run these engines on all types of fuel, from normal diesel, to home heating oil, to peanut oil and general vegetable oil. The three major fuels used in diesel engines today are petrodiesel, biodiesel and vegetable oil. Many people don’t know that biodiesel and vegetable oil are different fuels. Biodiesel is made from vegetable oil, but the properties of the fuel are very different. Here is a quick summary:
Petrodiesel or Fossil Diesel
- Hydrocarbon based oil
- Extracted from crude oil
- ~138,000 BTU per US Gallon
- 10%-20% less greenhouse gases than gasoline [EPA.gov]
Biodiesel
- Made from transesterification of vegetable oil or animal fat
- Works in many unmodified diesel engines
- ~130,000 BTU per US Gallon [NDSU.edu]
- Estimated 80% reduction in greenhouse gases versus normal transport fuels [CSIRO.au]
Vegetable Oil (SVO)
- ~130,000 BTU per US Gallon [NDSU.edu]
- No production required other than filtering
- Requires modifications to diesel engines
- Waste vegetable oil can be obtained free from restaurants
- Very little greenhouse gases such as carbon dioxide (Considered carbon neutral)
Hundreds of people all over the world have run diesel engines on biodiesel, vegetable oil and a combination of the two. All across the United States gas stations are starting to offer mixtures of petrodiesel and biodiesel. If you have ever seen fuel advertised as B20, that is 80% petrodiesel and 20% biodiesel. It has been shown that even slight mixtures of petrodiesel and biodiesel have dramatic reductions in greenhouse gas output in vehicles.
Vegetable Oil and Direct Injection Engines
There is a lot of talk online about how running a vehicle on vegetable oil will damage direct injection engines. Take a look the page titled Vegetable Oil and WV TDI engines for more information on running SVO in a modern diesel.
More Information:
US National Biodiesel Board: http://www.biodiesel.org/
HowStuffWorks.com Biodiesel: http://auto.howstuffworks.com/biodiesel.htm
Grease Works Page on SVO: http://www.greaseworks.org/svo
Greasecar SVO Kits: http://www.greasecar.com/