Do You Have to Modify a Diesel Engine to Run It on Vegetable Oil?

Dear Vanessa,

Do you have to modify a diesel engine in order to run it on vegetable oil, and is that the same thing as biodiesel?

— Randy Berinhout

Dear Randy,

Greetings from the base of Tungurahua volcano, nestled between the Andes and the Amazon.

Great question! You’re certainly not alone in asking for clarification. I’ve spent many hours in parking lots explaining the vanity plate on my ’84 diesel (“BIODSEL”), and the differences in the various fuels that can be used to power a diesel engine.

When Rudolph Diesel introduced his engine in 1900, at the World's Fair in Paris, it was running on peanut oil. Shortly after, the petroleum industry began cashing in on Diesel’s design by using a byproduct of petroleum distillation to power the engine. They called it diesel fuel.

My car can run on diesel (the fossil fuel variety), straight vegetable oil (SVO), and biodiesel (SVO that has been modified), or any combination of the three. That isn’t unusual: anything with a diesel engine -- plane, boat, motorcycle -- can run on diesel, SVO or biodiesel. SVO is a broad term, and covers a range of materials beyond vegetable oil including animal fats (chicken, tallow, lard and byproducts of omega-3 fatty acid from fish oil) and algae. SVO can be from virgin feedstock, meaning crops grown specifically as a fuel source, or recycled from other uses, such as used cooking oils (WVO for waste vegetable oil).

Here’s the catch: SVO will burn in a diesel engine but only if its viscosity (the thickness of a liquid) is brought down to a level similar to petro-diesel. Think about the leftovers in your fridge: the grease coagulates fairly quickly and doesn’t liquefy again unless it is heated. Running on SVO without making some modification can lead to some very sticky problems, literally.

There are two basic choices for dealing with the viscosity of SVOs: add a heating mechanism to the fuel line or tank, or process the oils. I do both. I use SVO -- always in the form of local WVOs – in a second fuel tank in the trunk of the car where the SVO is heated by a coil running from the radiator. The second option, modifying the oil, means using biodiesel. Biodiesel is made through a process called transesterification, a fairly simple process that uses lye to remove the coagulating properties of the oils. The byproduct of biodiesel processing is simple glycerine, used in soaps and other products.

The biodiesel I use is produced from WVOs recycled from local restaurants and university cafeterias. Of course, biodiesel can also be made from virgin oil feedstock. Soybean crops account for about 90 percent of U.S. fuel stocks.

That’s the basics: diesel engine originally designed to run on vegetable oil; no modification needed to run a diesel engine on biodiesel; heating mechanism needs to be added to run engine on SVO.

Now for the not-so basics. SVO and biodiesel have many advantages over petrodiesel:

• They are, theoretically carbon-neutral (they do not emit more carbon than they’ve absorbed).

• Their emissions are cleaner (including less asthma causing particulates)

• In the case of WVO, they can be locally recycled and produced and keep potential waste out of sewers and landfills.

• They are derived from renewable sources.

Thing is, renewable energy isn’t always sustainable.

I have subjected you previously, Dear Reader, to my mini-diatribes on biofuels, but here is a quick rundown on the negative impacts of biofuels. Too often, rain forests are burned to plant crops for fuel. Factoring in the carbon usage of agriculture, production and transportation, biofuels can no longer be considered carbon-neutral. The destructive and often poisonous environmental impacts of agriculture are overwhelming the planet. And growing crops for fuel has already led to rising food prices, and will only continue to create dangerous competition between fuel and food.

Hope that clarifies more than it confuses!

Vanessa