There's plenty of reading on these pages, grab a cuppa before you start :-)

Please note: This is not intended to be an exhaustive paper on the subject, but merely an introduction to what is a huge topic, with many branches and theories.


A little history….

The invention of the diesel engine is credited to Dr Rudolf Diesel. Having filed for a patent in 1892 his first working engine was completed the following year. By 1897 he had developed a suitable practical version with the incredible efficiency of 75% (Steam engines of the time were around 10%). In 1898 he demonstrated his compression ignition engine to the exhibition fair in Paris. This demonstration engine ran on peanut oil. Some of his earlier prototypes had run on coal dust using compressed air to inject it.

Dr Diesel envisaged an engine using plant oils, as demonstrated by one of his more famous quotes........ “The use of plant oil as fuel may seem insignificant today. But such products can in time become just as important as kerosene and these coal-tar-products of today.”

Up to the 1920’s these engines were primarily used in static applications and for marine purposes and continued to use plant oils as their primary fuel. Then with the help of the oil industry, the design of the engines fuel injection system was altered to enable them to use a less viscous fuel in a more compact injection process, a residue from the manufacture of petrol, this residue we now know of course as “Diesel”.





So how about using veg oil in a Diesel engine today?



Theoretically this is still OK, but some of the changes designed to enable use of “Diesel” fuel may hamper this ideal.

There are two primary obstacles to the use of veg oil today (or more if you count the car manufacturers, oil industry and governments). Firstly it is a far more viscous (thicker) liquid than the fuel you normally use, and secondly it will gel far more readily than petroleum fuels.

Well the first obstacle, that of higher viscosity leads us to consider the type of injection pump on the engine. Broadly speaking there are two types in use on the vast majority of diesel engines today. Bosch and Lucas/Cav designs. Of these the Bosch^* has proved itself far more robust and capable when using higher viscosity oils, thankfully the pump on the Surf although not manufactured by Bosch, is based on one of their designs and also appears to be proving capable of using veg-oil. The Lucas/Cav pumps have been shown to be prone to failure for a variety of reasons under various conditions when used with veg-oil. Possible reasons and potential cures for the Lucas/Cav issue are beyond the scope of this article, as they are not relevant to the Surf.

OK, so the Surfs pump appears to handle the oil, what next? Well just because it can handle it is not the end of the story. The thicker fuel will not spray from the fuel nozzles in exactly the same pattern as the diesel fuel does. The colder the oil, the greater the difference there will be in this pattern. This spray pattern has been carefully designed to ensure a number of things, efficient burning of the fuel and minimising coking of the various components being among the primary considerations. Any alteration in this spray pattern can have a negative impact on these requirements.

To overcome the problems posed by the increased viscosity of the veg-oil, many solutions have been tried. These involve either modifying the oil to reduce its viscosity, or modifying the fuel system to accept the greater viscosity.

Modifying the oil splits further into two main groups, reducing the viscosity by adding other ingredients or chemically converting it into Biodiesel. Converting it to Biodiesel produces a fuel which can be used in virtually any modern diesel engine without further modification. Whilst it is a process which can be done at home, it does involve the use of potentially dangerous chemicals and is beyond the scope of this article. Adding other ingredients to lower the viscosity is the method favoured by many Surf owners, the other ingredients range from white spirit to unleaded petrol to diesel fuel, and other liquids. I firmly believe the best ingredient to use is diesel fuel. The others have not been as well proven to be viable long term alternatives, and bring with them many other issues including increased volatility and the potential to damage fuel system components.

The other route is to modify the fuel system. This will involve heating the veg-oil to reduce its viscosity. Various methods have been proposed including utilising exhaust heat, engine coolant heat & electrical methods. The exhaust is generally ruled out as it cannot be easily controlled, and could under certain circumstances lead to overheating of the fuel or even fire. Virtually all will employ engine coolant to heat the fuel via a heat exchanger and many will supplement this with a degree of electrical heating. This electrical portion is often used only until the engine reaches operating temperature, at which point it may be turned off, with the heated engine coolant performing the task of heating the fuel. These types of conversions usually involve fitting a second tank to enable the engine to start and shut down on diesel fuel, this ensures it does not consume any veg-oil until it has been heated sufficiently, and that there is diesel in the fuel lines prior to every start. Many manufactures offer kits to convert diesel to such twin tank systems with varying degrees of complexity. One company, Elsbett in Germany even offer a conversion which enable you to run on 100% veg-oil, including at start-up etc, without the need for a second tank.


^* Note: Some newer design Bosch pumps are very similar to the Lucas design and have been shown to be unsuitable for use with veg-oil, those fitted to the Surf are OK (at least up to 08/2000 anyway, later engines are of the D4D type, I've no idea what fuel pump they use)