Vegetable oil will react very similarly to diesel fuel under the conditions inside a diesel engine; i.e. when it is highly compressed, it will heat up and ignite, causing the air in the cylinder to expand, and to push the pistons, in time. If you burned straight unprocessed vegetable oil, however, the fatty acids in the oil would start to congeal and harden (coke up) on the inside of your engine as well as in your fuel injectors, eventually leading to big, expensive engine problems.
Therefore, it is necessary to process your oil to remove the fatty acids-- making the oil more similar to diesel compositionally, or to otherwise devise a system to keep your engine clean of residues from unprocessed oil.
Following is our procedure for edible waste oil transesterification, which we used on our cross country trip. Please always use extreme caution when working with these ingredients.
Free fatty acids will increase with the amount of time vegetable oil has been heated-- oil which has been used for cooking will require more of the reactive agents-- lye and methanol-- than fresh oil. The presence of too many free fatty acids will retard or stop the reaction which produces biodiesel, so it is necessary to detect the exact amount of LYE (Sodium Hydroxide-- or NaOH) needed to neutralize the acids. Adding too much or too little NaOH will just make excessive amounts of bi-product (soap).
Dissolve 1 gram NaOH (Sodium Hydroxide- Red Devil Lye) in 1000 ml. of water. This is your NaOH solution.
Dissolve 1ml. of Wasted Vegetable Oil (WVO) in 10 ml. Isopropyl Alcohol(IPA). This is your WVO solution.
With an eyedropper, drop the diluted NaOH into WVO mixture a milliliter at a time. Count the drops. After each ml drop check the ph level of the WVO solution with standard ph paper-- you will see an eventual rise in the ph level. Continue to add the NaOH solution into the WVO solution, a drop at a time, until it reaches a ph of 8-9.