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How to make your own fuelHow to make a simple heat exchanger
Can I burn straight vegetable fat in my diesel engine?If my engine runs on SVO, then can I burn WVO?
How can I know if my engine will run on Straight Vegetable Oil?
There is one simple answer ... Try it!
Do not simply put 100% SVO into your fuel tank and set out on a long drive. Not only might this be illegal, it would also be very stupid. Before you drive on the road with a vehicle powered by any form of un-taxed hydrocarbon fuel you must register with HM Customs & Excise as a substitute fuel producer. But also you should test your engine first without risking any blockage in the fuel supply system. Most problems will be discovered not when doing the tests but when you try and re-start the engine from cold. It is therefore a good idea to plan when you will carry out the tests, for example on a Friday or Saturday, so you will have plenty of time to deal with any refueling if the engine will not start having been left out in the cold over night. Do not test the engine when you have to use the vehicle for an urgent journey first thing the next morning!
To do the test you will need some clean new vegetable oil (preferably rape seed oil), an empty plastic milk or vegetable oil bottle, and two short pieces of fuel pipe. Start the engine and let it warm up. Identify the fuel supply and return pipes that run from the fuel tank into the engine compartment. The supply pipe will run to the fuel filter and then to the injector pump. The return line will run from the injector pump back to the fuel tank. Find a safe place where the empty bottle can be mounted, and fit a tie or some string or wire to keep it safely without risk of tipping. Do not mount it where it can touch the exhaust or the hot parts of the exhaust manifold. Stop the engine and remove the fuel lines from the fittings and slide on the two sections of fuel pipe so the ends of the supply and return can be inserted into the bottle. Fill the bottle three quarters full with rape seed oil. You are now ready to carry out the test. I suggest you have someone else with you to help operate the starter from the cab.
Restart the engine in the normal way. It should be already warm, in other words run the engine till it is warm before disconnecting the fuel pipe links. The fuel pump should suck through the new fuel and any air that may have been included into the fuel lines. Try to avoid letting air into the pipes, but in all engines I have tested the pump sucked the air pockets through easily without stopping the engine. Do not rev up the engine excessively, there is no need. Just listen to any change in the engine tick-over noise, and general 'clatter' of the engine. Smell the exhaust and you should notice a sweet appetizing smell and not the acrid smell of burning derv. In all the engines I have tested this way, the noise of the engine changes, and the sound is smother and becomes more of a 'grunt' than a rattle.
You may see a white / yellow froth build up on the surface of the fuel in the plastic bottle. This is caused by little bubbles in the return oil as a result of compression and then sudden de-compression. At first the vegetable oil is too thick at normal temperatures to allow these tiny bubbles to disperse, but they will clear as soon as the temperature of the oil increases. The appearance of this white froth is normal when starting from cold. It should disappear after about 15 minutes of running. If the engine does not seem to run well, then heat some vegetable oil in a saucepan on the kitchen stove till it is about 100 deg centigrade (it just stops 'popping'), and then put this in the milk tub. If this improves the engine performance then you will definitely need a fuel pre-heater.
If the test seems to be going well, then check the fuel level in the plastic tub, and and check the engine temperature, and close the bonnet, and do a test drive. Do not drive on the road as this is illegal using untaxed fuel. Find a private road, beach or car park somewhere. If after this test you feel the engine will work well on SVO then try connecting the fuel lines through the normal fuel filter and fuel tank. Fill the tank with 50% Derv and 50% SVO, and repeat the test but this time running from the fuel tank. Gradually increase the proportion of SVO. In doing this test you may reach the point at which the performance of the engine degrades. You may find that the engine will not want to start on SVO when it is completely cold, but it will run OK if it is already warm. If this is the case then try adding about 5% by volume of kerosene. If this improves performance and cold starting, then you will need to fit a fuel pre-heater. Do not leave the vehicle in cold conditions with more than 50% SVO mix in the fuel tank, without adding a dash of kerosene, in case the engine will not restart from cold. If you do experience starting problems then disconnect the fuel pipes again, and start from neat DERV in the milk bottle until the engine starts and warms up. Then add a bit more kerosene to the fuel in the main tank.
Careful observation when carrying out these tests will enable to to decide what level of permanent conversion is necessary to enable your engine to burn SVO. Some engines need no alterations - Mercedes engines for example, and some like my VW Passat need hardly any. Generally, it seems that Mercedes and VW engines are especially accepting of bio-fuels, and SVO. But other engines may run on SVO if there is a heated fuel filter or pre-heater.
The first adaptation to try may be the installation of a heated fuel filter. I have used one removed from a Peugeot car found in a scraper. It was in a dreadful condition, and needed to be stripped and thoroughly cleaned. It was fitted on the bulkhead next to the normal fuel filter, and connected to the water supply to the cab heater. The fuel passes through the middle core of the filter and down to the heating element in the base, which is heated by the water coolant from the cylinder block. The hot fuel then rises up through the filter papers and goes to the injector pump. The main advantage of this form of heating is to allow any animal fats in waste vegetable fat to pass through the filter. These stearines tend to solid at normal temperatures, and will block normal un-heated fuel filters (as I know from my own experience!).
If you still have problems starting, or running on SVO, then you may need a heat exchanger. I made one from standard copper plumbing fittings. I am now experimenting with different designs. My first trial design was fitted into the maim hot water pipe from the engine to the radiator. This may not be the best solution, as this pipe only floods with hot water after the engine has warmed up and the thermostat has opened. My next designs are fitted into the water circuit that provides immediate heat to the cab and screen warming system. This is not affected by the thermostat, and makes use of the heat from the engine as quickly as possible.
Even with a pre-heater, you may find the engine does not start well or does not run well until the heat exchanger is warmed up. It may be necessary to run the engine whilst stationary for about 10 minutes until all the water pipes and the fuel is sufficiently warm. I am designing a thermostatically regulated electric heater to heat up a small quantity of fuel immediately before it enters the injector pump. This will hopefully overcome any problems in starting, even in cold conditions.
It is one thing to test a small sample of SVO in your engine, but another to run an engine on SVO for a long period of time. That is not to say that damage will certainly be caused to the engine. Some engine manufacturers have suggested that an engine running on vegetable fat will last many times longer than one running on DERV or ULSD. The fact is that this is an unknown territory. We need to test the use of SVO in all kinds of vehicles, but to do so cautiously, and not fool-hardedly. It is always important to maintain the engine properly, check water levels, and check oil levels and make sure you always carry spare fuel filters in the vehicle in case of blockage. Watch the exhaust for excessive sooting, and every few months go back to running on DERV to remind yourself what the comparison between the two types of fuel is.
One problem we have often heard about is that using bio-fuels there is a blockage in the fuel filter caused by the lifting of junk that has been deposited in the fuel tank over a long period of time. Also, bio-fuels are sticky, and will attract fluff into the fuel tank opening if the lid is not always kept closed.
If you do test your engine as described above then please let me have a report on your findings. It all helps us to build up a picture of what will work on what type of engine.
If my engine runs on SVO, then can I burn WVO?
How to make your own heat exchanger
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John Nicholson 3rd January 2002 June 2007
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