General ‘Homebrew’ Biodiesel Information

Posted By on April 1, 2005

Graydon Blair’s excellent FAQs and links:

Vegetable Oil can be used in some diesel engines in three main ways:

    1 – Directly at 100% concentration in a heated two tank system.
    2 – Blended in various percents with other fuels in heated or unheated systems depending on the percent of veggie-oil blended and the operating climate.
    3 – Chemically converted into biodiesel.

This list focuses primarily on the third way; chemically converting vegetable oil into biodiesel.

A Little About Biodiesel:
Biodiesel is the name commonly used to describe a fuel that can be made from any organic oil by chemically altering it’s molecular structure to run in an unmodified diesel engine.

The chemically altering it part involves mixing a reagent (typically Sodium Hydroxide- NaOH or Potassium Hydroxide- KOH) with an alcohol (typically Methanol or Ethanol) to make a sustance called Methoxide (or Ethoxide if Ethanol is used).

The organic oil is then heated to a fairly high temperature (approx. 120-130 F 48-54 C) and the methoxide mixture is then mixed into the oil. The oil & methoxide is then mixed for a period of time (typically 1-2 hours) and then allowed to cool and settle for a period of time (typically at least 8 hours).

After it’s cooled for a period of time, a settling will occur in the mixture. The substance that falls to the bottom is called Glycerin and is removed from the mixture by draining it off. Based on how successful the reaction is and how much alcohol and reagent is used, there may be another layer of soap that is also removed. The top layer is a substance called Biodiesel.

Biodiesel’s chemical name is “Fatty Acid Methyl Ester” (if methanol is used) or “Fatty Acid Ethyl Ester” (if ethanol is used).

The Biodiesel is then either washed or allowed to settle for a period of time. If washed, it is washed by either mist-washing, bubblewashing, or both. After it’s washed it is then dried to remove excess moisture. If settled, the biodiesel simply is allowed to sit for a period of time to allow the impurities to settle to the bottom. Once settle, washed, and dried it may be filtered and then can be used as a fuel in most diesel engines without any problems.

Use In Diesels:
Biodiesel can be used, for the most part, in unmodified diesel engines. It can be blended with petro diesel fuel in any ratio and is commonly blended in blends of 20% biodiesel to 80% diesel when sold commercially. It can also be run straight in a diesel engine.

When used straight (100% biodiesel), some precautions need to be followed. Biodiesel, depending on the organic oil it was made from, tends to gel up. Petro diesel also will gel at lower temperatures, but Biodiesel typically gels at higher temperatures than Petro diesel.

By mixing Biodiesel with either Petrodiesel or various grades of diesel fuel (commonly called Kerosene or Jet Fuel), it can be used in lower temperature settings. For temperatures below freezing, most recommend no more than a 50% mixture of biodiesel in an unmodified diesel engine.

Biodiesel also may cause older fuel lines to break down over time with extended use of high blends (50% or higher). This is due to the solvent properties in Biodiesel breaking down the older rubber fuel lines. Most people report no problems with the use of Biodiesel in their older engines, but there have been some cases where fuel lines have started to leak and are in need of replacement. If the fuel lines are replaced with biodiesel compatible ones, the problem is resolved.

Biodiesel vs. Vegetable Oil:
Quite often, Biodiesel is confused with running Straight Vegetable Oil in diesel engines. Both can be done and both are viable alternative fuels in diesel fuels.

Biodiesel is typically “thinner” than straight vegetable oil at room temperature, although by modifying the fueling system to heat the fuel before it’s introduced to the engine allows for straight vegetable oil to be used relatively easily in diesel engines.

The easiest way to remember the difference is that:

    1- Straight Vegetable Oil is just the organic oil with no modifications to it except filtering when used as a fuel.
    2- Biodiesel is an organic oil that has been chemically altered and then it is used as fuel.

Additional Resources:
The Collaborative Biodiesel Tutorial
– This great resource has several articles dedicated to helping you get started making biodiesel. You can even learn how to build the equipment to make the biodiesel yourself.

Here’s a few links directly to great articles:
Getting Started Article:
How It’s Made graphic:
Building A Processor:
Building A Wash Tank:
Performing A Titration:

There are a LOT of little thing’s I’ve left out and there’s still a lot of “wiggle room” for how biodiesel is made. It can be made several different ways, but the basic premise is still the same; convert an organic oil into biodiesel by chemically altering it through the use of a reagent and an alcohol.


Desultory - des-uhl-tawr-ee, -tohr-ee

  1. lacking in consistency, constancy, or visible order, disconnected; fitful: desultory conversation.
  2. digressing from or unconnected with the main subject; random: a desultory remark.