Winterized Biodiesel And Straight Vegetable Oil Conversion

Energy
Electricity -- Biodiesel -- Heating and Cooking -- Winterized Biodiesel

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At Dancing Rabbit we've been trying to use 100% biodiesel in our vehicles since 1997. But living in a four-season climate we've had trouble with fuel gelling during the winter, often forcing us to use petrodiesel. While petrodiesel is known to gel on the coldest of days (below 0 degrees Fahrenheit), biodiesel can start gelling as soon as 40 degrees F. Additives to petrodiesel can lower the gelling temperature, but we have not had success with additives in biodiesel.

In our ongoing efforts to end our use of fossil fuels we've modified our 1998 Volkswagen Jetta so that it can run on biodiesel in the winter. This same modification allows us to run the Jetta on unmodified vegetable oil during the summer.

The system we used was based on plans in From The Fryer To The Fuel Tank by Joshua and Kaia Tickell. This book is a must read for anyone using biodiesel or vegetable oil as a fuel. The basic system is to install an extra fuel tank, heated by coolant from the engine. The vehicle is started on a non-gelling fuel (petro in winter, biodiesel in summer) and switched to the gellable fuel after it has been heated. Below we outline the system we used, but these sort of solutions are now available for purchase. The photos here are from the first modification we did, of a 1992 Jetta.

The Heated Tank

Following the Tickell's instructions we put together a ten-gallon tank that fit neatly into the trunk of the Jetta. The first step was to obtain all the various hoses, fittings, and other parts necessary for the conversion. Then we took 25 feet of 3/8ths inch flexible copper pipe and bent it using a tubing bender to fit as much of it into our tank as possible. Hot coolant from the engine will run through this "heat exchanger," and heat the fuel in the tank.

We then built a cardboard model of the eventual fuel tank (you wouldn't believe how helpful this model was; do not skip this step!) and connected the copper coil to the model using two bulk head fittings. Holes for the fuel filler plate and the fuel level gauge were made on the cardboard model. The model was then tested in the trunk to make sure there was clearance for all hoses and connections.

The tank model was taken to our local welding shop where they made an aluminium version and added on brackets to secure it to the vehicle. Note how we placed all holes in the tank in the top to minimize leakage (but not eliminate, in early testing we still had leaks when the tank was full). Unfortunately, our welder did not want to weld the copper and aluminium together as the Tickells suggested, thus requiring the bulk head fittings. After testing the tank for leaks and cleaning out all metal shavings, it was ready for installation.

Hoses and Fitting

We took the tank, the Jetta, and a box full of parts to our local fix-it shop. Luckily the folks who run the shop are friendly and open to new ideas. After installing the tank in the trunk we ran 5/8th inch coolant hoses from the engine compartment under the car and to the tank in the trunk. Under the hood these connected to the hoses running to the heater core (the device which heats the passenger compartment). To keep the fuel warm on its journey from trunk to engine, the fuel line from the trunk runs in a "hose within a hose." The inner hose holds the fuel, the outer hose has hot coolant. At first we used a polyethylene hose for the fuel line as described in From the Fryer to the Fuel Tank (pictured here), but soon we had problems with the fuel line rupturing and mixing fuel with our coolant. We learned that polyethylene isn't rated to withstand temperatures above 170 F and so we switched to copper tubing. Another option would have been to use PEX which is a high temp version of polyethylene.

In the engine compartment the fuel line connects to a solenoid switch which allows switching between two fuel tanks with a toggle switch on the dashboard. After the solenoid we installed two fuel filters, one at 30 microns and the other at 10 microns. The second fuel filter has a special coolant based heater built into it to give the fuel one last burst of heat before going to the engine (this feature is only necessary for vegetable oil fuel and could be skipped if just using biodiesel.)

Back in the trunk we installed a fuel temperature gauge and a thermoswitch. The thermoswitch, wired in series with the solenoid switch, prevents you from trying to use the heated tank before it is hot enough. All the wiring for the gauges and switches was run to the dashboard, left of the steering wheel. Here you can see the fuel level gauge on top, a fuel temperature gauge below, and the toggle switch for the solenoid.

How It Works

On a cold winter day the driver starts the Jetta on the main tank, which has a non-gelling blend of biodiesel and petrodiesel. Immediately the driver flips the switch to the heated tank and begins driving. After about five miles (for biodiesel) the fuel in the heated tank is warm enough and the thermoswitch engages, allowing the engine to pull fuel from the heated tank. Near the end of your drive, you switch back to the main tank to purge the fuel lines of any gellable fuel (usually five miles). In the summer we use the same system on straight vegetable oil.

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