The diesel engine is named after the original developer of the engine, Rudolf Diesel, who initially attempted to run the engine with coal dust and later redesigned the engine to run with vegetable oil. Several similar efforts of the early 1900s were reported. Since then, the R&D efforts of using straight vegetable oils as a diesel substitute or alternative diesel fuel have continued or received public interest in response to escalating and fluctuating petro­leum prices.

If properly modified, most diesel engines on automobiles can be run on vegetable oils, that is, SVO or PPO. Principal modifications involve reduc­tion of viscosity and surface tension of SVO before injection of the fuel. High viscosity and surface tension of vegetable oils, if not altered, can cause poor atomization of the fuel, which results in incomplete combustion. Incomplete combustion causes coking or carbonization, which produces polycyclic aro­matic hydrocarbons (PAHs), soot, or coke. The reduction of viscosity and surface tension can be achieved via preheating of the fuel before its injection, which can be accomplished using the waste heat of the engine or the automo­bile’s electric power. In such a case, an additional tank of normal diesel (i. e., petrodiesel or biodiesel) would still be needed in addition to the main SVO tank for smooth engine operation. The cold engine is started with normal diesel and once the engine gets warmed up, the fuel is switched from nor­mal diesel fuel to vegetable oil which is preheated using a heat exchanger. In a very cold climate, this limitation in cold start is potentially a significant hurdle to overcome.

Alternately, an innovative blend chemistry may be devised for property modification of vegetable oils for their direct use in diesel engines. Vegetable oil can be mixed with other fuels or chemicals such as kerosene, diesel, and gasoline, thereby reducing the viscosity (in particular, kinematic viscosity) and surface tension of the blended fuel. The blending chemical/fuel typically

Fatty Acid Compositions of Common Edible Oils3

TABLE 2.3 Oil Unsat./Sat Ratio Saturated Monounsaturated Polyunsaturated Capric Acid 00:0 Laurie Acid 02:0 Myristic Acid 04:0 Palmitic Acid 06:0 Stearic Acid 08:0 Oleic Acid 08:1 Linoleic Acid (u>6) 08:2 Alpha Linolenic Acid (u>3) 08:3 Almond Oil 9.7 — — — 7 2 69 17 — Canola Oil 15.7 — — — 4 2 62 22 10 Cocoa Butter 0.6 — — — 25 38 32 3 — Cod Liver Oil 2.9 — — 8 17 — 22 5 — Coconut Oil 0.1 6 47 18 9 3 6 2 — Corn Oil (Maize Oil) 6.7 — — — 11 2 28 58 1 Cottonseed Oil 2.8 — — 1 22 3 19 54 1 Flaxseed Oil 9.0 — — — 3 7 21 16 53 Grape seed Oil 7.3 — — — 8 4 15 73 — Olive Oil 4.6 — — — 13 3 71 10 1 Palm Oil 1.0 — — 1 45 4 40 10 — Palm Olein 1.3 — — 1 37 4 46 11 — Palm Kernel Oil 0.2 4 48 16 8 3 15 2 — Peanut Oil 4.0 — — — 11 2 48 32 — Safflower Oilb 10.1 — — — 7 2 13 78 — Sesame Oil 6.6 — — — 9 4 41 45 —

Source: http://www. scientificpsychic. com/fitness/fattyacidsl. html; http://www. coimectworld. net/whc/images/chart. pdf; http://curezone. com/ foods / fatspercent. asp

Note: Percentages may not add to 100% due to rounding and other constituents not listed in the table. Where percentages vary, average values are used. a By weight of total fatty acids. b Not high-oleic variety.

is chosen from lower molecular weight hydrocarbons. This type of blending is often referred to as "cutting," "diluting," or "cosolvent mixing." However, there are some concerns regarding blending, which are largely based on higher rates of wear and tear in conventional fuel pumps and piston rings when using such blends. Advances in automobile component design includ­ing fuel injectors, cooling system, and glow plugs as well as in materials of construction are expected to be made.

As an example of recent advances, automobiles powered by indirect injec­tion engines equipped with in-line injection pumps are capable of running on pure SVO in most moderate climates, except during cold winter tem­peratures. Some of these vehicles are equipped with a coolant-heated fuel filter, which functions as a fuel preheater that helps reduce the viscosity of the SVO.