school bus Diesel engines last a long time, half a million miles or more is not unusual, . What is clear is that “any diesel” is an exaggeration. Some diesel engines are more suitable than others. Many vegetable oils have similar fuel properties to diesel fuel, except for higher viscosity and lower oxidative stability. These differences should be able to be overcome. Now you get vegetable oil that can substitute for #2 diesel fuel. This is used for engine fuel or home heating oil. A grease car will run on vegetable oil. It will run on used vegetable oil.

Vegetable oil discarded from restaurants and used as fuel is regarded as waste vegetable oil (WVO). Straight vegetable oil is (SVO) or pure plant oil (PPO). For engines designed to burn #2 diesel fuel, the viscosity of vegetable oil must be lowered to allow for proper atomization of fuel, otherwise incomplete combustion and carbon build up will ultimately damage the engine.

Basic diesel Engine Theory

Modern engines are fitted with injection systems designed to deliver and properly atomize diesel fuel which has a viscosity of approx.. 8 centistokes, common vegetable oils are 10-20 times more viscous (thick). Spraying this through an injector designed for diesel would be like spraying butter through a spray water bottle. This fluid is so much more viscous. An improper spray pattern will result in incomplete combustion, incomplete combustion will result in carbon deposits being formed in the engine which will destroy the engine. There are several ways to reduce the viscosity of vegetable oil, the simplest is simply heating it up. When vegetable oil has been heated to 160F its viscosity is very close to that of petroleum diesel.

The other issue which needs to be dealt with is the polymerization of vegetable oil when it contacts metal below an optimum temperature. The simplest way to explain this is with a simple analogy: Imagine placing a pan on the stove, pouring a small amount of vegetable oil in the pan, and turning the heat to high. The pan will begin to heat up and as it does it will heat the oil, around 300F the oil will start to smoke, then turn black, stick to the pan, and destroy it. With another pan turn the heat on high again. When the pan gets to about 600F throw a tablespoon of oil in the pan, you will notice that the oil is skittering around the pan on a layer of vapor, none of the oil is sticking to the pan and none of it is turning to carbon.

This same principle applies inside the combustion chamber of your engine, so injecting oil at any temperature into a combustion chamber which is not at operating temperature will result in carbonaceous deposits being formed on the piston crown and cylinder walls again destroying your engine. We now have two major problems to overcome.

1) The vegetable oil must be heated to at least 160F before being injected so that it can be atomized properly by the injectors.
2) The engine must be at operating temperature before any oil is injected.

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 180F by the time the engine is up to operating temperature, we have a ready heat source. Since the engine must be at an operating temp of 180F 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 180F we can easily produce fuel at above 160F meeting the requirements of problem #1.

So we will need to have a vehicle with two independent fuel systems, one for diesel 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.

Several manufacturers developed systems which enable the use of vegetable oil in a diesel engine, however upon inspection its been found that they all were lacking on one or all areas required for a functioning vegetable oil fuel system. The most common error discovered was that nearly every system relies on a small inefficient heat exchanger in the fuel tank to provide all the heat to bring the vegetable oil to injection temperature. One such system was installed in a VW Diesel pickup, the round tank was installed in the bed under a canopy. On a 55F day it was driven for 45 minutes in traffic. The engine came to temperature quickly, but the temperature gauge installed in the tank had barely moved, after 45 minutes it read an oil temp of only 120F. It was realized that the previous owner had driven for thousands of miles injecting oil at no more than 120F It became obvious that simply heating the tank with a coil and running the vegetable in a PEX fuel line inside a coolant line was not enough heat. In addition this system was being required to heat the full volume of the fuel tank to injection temperature. This meant that each time the grease car ran, it had to heat 15 gallons of vegetable oil to 160F before It could be used as fuel. This is of little use in the city and would only be a benefit on cross country trips.

It was also discovered that many of the systems on the market routed the unused fuel back into the inlet side of the injection pump so that they did not have to run a return line back to the fuel tank. While this meant that the heated fuel was not sent back to the tank (which needed to be at injection temperature anyway) it also meant that in order to purge the fuel system, the fuel in the lines, injectors and injection pump had to be consumed in order to be replaced with diesel fuel before shutdown. Because this method only diluted the vegetable oil present in the loop, the same volume of fuel must travel through a looped systems 6 times to assure that no vegetable oil is present. This leads to very long purge times and a tendency to trap air in the fuel system leading to fuel starvation. Some systems went as far as to simply permanently “Loop” both the diesel and the vegetable oil which is a particularly poor idea as diesel is a poor lubricant to begin with and when heated becomes a destructive force in the fuel system. This is why most diesel engines actually have a fuel cooler in the return line.

So we will look at a new design.. Each component was taken separately and designed to exceed its system requirements. We need the following components to have a functioning vegetable oil fuel system which will not result in engine damage:

1) A tank to contain the vegetable oil. It should be constructed to the same specifications as the fuel tanks used in race cars. The tank should have an internal baffle to prevent the fuel from sloshing from side to side. It should be constructed from a material which will not react with the vegetable oil it contains. The area around the fuel pickup tube should be heated to insure that the fuel is thin enough to be drawn through the fuel lines without undue restriction.

2) Fuel lines to supply fuel to the engine and return unused fuel to the tank should be heated to thin the fuel enough to be drawn through the lines without undue restriction.

3) A fuel filter which will also need to be heated so that the fuel can be filtered easily. Such filter should be an easily replaced part and readily available.

4) A final fuel heat exchanger capable of using engine coolant to heat fuel to the required temperature at maximum fuel flow.

5) Switching valves to switch between the two fuel systems. These should be independently controlled so that no cross contamination of fuel takes place and to speed the purging of fuel from the system.

6) A controller to switch the valves when the fuel is at the proper temperature and not before, to provide status indicators (Diesel mode, VO mode) to the driver, to provide an alarm if the vehicle is shut down while running on vegetable oil and to control the purging function so that the driver need minimal interaction and can devote his or her attention to driving as this is, after all, the point of the exercise.

There are new innovative systems out there now and as far as finding the right grease car setup it will take a little studying but the designs are out there.

Frederick Carter
Grease Car is the Word

Discover Tho Secrets of The Most Sought After Alternative Fuels & The Future of Energy”