Conversion of F250 Powerstroke 7.3L Diesel to Waste Vegetable Oil
Most diesel engines are capable of running on a wide variety of fuels. In the last several years converting diesel engines to run on waste oil byproducts has been becoming increasingly popular. Several years ago I converted my 2002 Ford F250 to run on waste vegetable oil. The design was a collaboration of my own ideas combined with those of Jason Crawford's. Since that time, Jason Crawford has continued to innovate his design, which was later to become the Vegistroke™ available from Dinofuels Alternatives. I have recently purchased his latest kit myself, and will soon be updating my truck. This is an overview of my original conversion for those that are considering building their own conversion, or just curious how they work. For anybody that is looking to purchase a conversion kit I would highly reccomend they check out Jason's products at Dinofuels Alternatives. They are by far the highest quality conversion products available on top of extremely good customer service. His kit price is less then what everything I bought here added up to and it is a much more complete solution.
Not all engines convert to alternative fuels exactly the same, but there aften many simularities. The most two important factors for vegatable oil is that the fuel NEEDS to be clean and dry. While it is not difficult to filter the oil, removing any miniscule amounts of water can sometimes prove tricky. If the water is not removed it will cause cavitation in the injection pump or injectors which will signifcantly reduce the life of those parts. The second most important part is that you want the vegetable oil to be hot when it is injected. Heating the oil reduces the viscosity, bringing its physical properties closer to diesel and also helps to ensure complete combustion. How hot it needs to be is debated, but 160F is a typical goal. Another important aspect of reliably using vegetable oil as a fuel is to startup and run the engine on standard diesel or biodiesel until the engine is warm and the vegetable oil is hot enough for injection. It is also important to purge all vegetable oil back out of the engine before shutdown so that the next startup can be on diesel again.
The Ford Powerstroke Super Duty 7.3L (built by International / Navistar) has some unique advantages that set it apart for alternative fuel usage. First is the fuel injection system. These engines do not contain an injection pump. Instead they have an injector at each cylinder that uses high pressure engine oil to pressurize the fuel for injection. The injectors are fed by a fuel rail that is cast directly into the head of the engine. This is an advantage because this fuel rail acts as an extremely good final heat exchanger. This design also allows a configuration of check-valve's to control which fuel you are using. It also enables the use of an extra valve to purge the vegetable oil from the head at shutdown, reducing the purge process to only a few seconds instead of the 10-15 minutes or more required by some engines.
The major components of my orginal conversion are:
- 50 Gallon marine poly tank
- Hotstick alluminum tank heat-exchanger
- Aeromotive A1000 Fuel Pump (I now reccomend a different pump, the SVO Fuel Pump from Dinofuels Alternatives)
- Mallory 4305M bypass Fuel Pressure Regulator
- Davco 234+ Fuel Filter
- Check-valved switchover per Jason's design
- Flatplate brick style final heat exchanger - (later removed)
The system's switchover is based off of Jason's idea to use check valves and differential pressures to control switchover and to have added reliability to the fuel system. This method keeps two independant fuel systems right up to the motor, so that in a failure with a pump or plugged filter, you can still drive on diesel. In fact, the switchover back to diesel is so smooth, you wouldn't even know if you didn't see it on the pressure gauge. I believe Jason has a patent on the check valve switchover method. To the right is a diagram that shows the basic layout of my conversion. I simplified the diagram by leaving off the coolant hoses to the various parts. The coolant is sourced and returned via the cabin heater hoses. The final heater exchanger, aluminum fuel lines (Hose on Hose), Davco filter, and Hotstick tank heater are all heated by the coolant, in that order.
I colored the components based on which fuel is flowing through them. As you can see the stock fuel system is mostly unaltered. The only change is that instead of being routed straight from the stock filter to the heads, it goes through a check valve and into the checkvalve manifold instead. The stock design is to have the heads dead-headed, meaning that fuel goes into the heads at the same rate it is consumed, and the stock fuel return is from the integrated FPR (Fuel Pressure Regulator) in the stock filter housing. This is a nice plus, because it keeps oil very hot. The other side of each fuel rail in the head has a port that is plugged in the stock configuration. The WVO (Waste Vegetable Oil) FPR output is attached to these ports, and then set to a pressure high enough that it will not bypass any fuel at the stock pressure. The veggie FPR and purge valve actually have just WVO in them most of the time, but I colored them as both fuels because a small amount of diesel will pass through them during the fast purge cycle.