Using vegetable oil as a fuel in a modern diesel engine has two challenges: the viscosity of vegetable oil is unsuitable for use in modern fuel injectors; and the polymerization of vegetable oil when it hits hot metal at below a certain temperature threshold. The oil must be heated to 160° F to reduce its viscosity to a point comparable to that of diesel, and the engine must reach 180° F before the oil is injected to avoid the polymerization problem.

Since we have an engine which is cooled with coolant (50% Distilled water, 50% Ethylene Glycol) we have an abundance of coolant which has been heated to 180° F by the time the engine is up to operating temperature, we have a ready heat source. Since the engine must be at has an operating temp of 180° F we have met the requirements set by problem #2 (engine at temp), and by using a coolant to fuel heat exchanger with the coolant being 180° F we can easily produce fuel at above 160° F meeting the requirements of problem #1.

So we will need to have a vehicle with two independent fuel systems, one for Diesel (or Biodiesel) and one for the vegetable oil. We will start the vehicle on diesel fuel and run it on that fuel until we are at operating temperature, at this point we can supply vegetable oil at better than 160F and can switch the fuel supply. Of course when we shut the vehicle down the fuel system will still be filled with vegetable oil, which will cool and become useless as a fuel prohibiting us from restarting the vehicle as the conditions to solve problems 1 & 2 are no longer being met. To solve this issue we will need to purge the vegetable oil in the fuel system with diesel before we shut the engine off.

—from the Frybrid website

The vehicle starts on diesel until the engine and coolant reach the appropriate temperatures, then switches over to VO. To avoid startup problems, the fuel system needs to be purged of VO prior to shutdown.

While some VO systems rely on only a small in-tank heat exchanger to heat all the fuel in the tank to injection temperature, the Frybrid system uses four heaters:

• A welded high-efficiency coiled heat exchanger in the aluminum, baffled tank with the fuel pickup positioned directly in its center. This assures that all fuel being drawn from the tank is liquefied and lessens the strain on the injection pump and or fuel pump. All internal tank connections for both fuel and coolant are TIG welded to insure a leak-proof system. The integral fuel reservoir prevents fuel starvation when cornering, stopping or accelerating when low on fuel. None of the metals in contact with the fuel tank are reactive and the heat exchanger has more than 30 sq ft of surface area.

• A heated fuel line connected directly to the top of the fuel tank.

• A heated fuel filter, which incorporates a 14-plate flow through heat exchanger through which all fuel must flow before being filtered. This unit heats the fuel very efficiently insuring that the filter will not slow the flow of fuel even in cold climates and utilizes a readily available diesel filter element with an integral drain.

• A final fuel heat exchanger which on its own is capable of getting all fuel used by the engine to injection temperature as soon as the engines coolant is at 180° F.

Frybrid’s solid-state vegetable oil fuel system controller monitors engine coolant temperature and seamlessly switches the engines fuel supply from diesel or biodiesel to vegetable oil only when the vegetable oil is at the proper temperature preventing the injection of cold vegetable oil which results in engine damage.

The controller also warns the operator if the vehicle is shut down on vegetable oil, provides system status indicators and automates the purge cycle allowing for faster engine shutdown.

(A hat-tip to Forest!)

Resources:

• Elbee, the Freedom Machine