Although biodiesel performs well in almost all diesel engines when it meets recognised quality standards, it can cause all manner of issues if it does not meet the required standards. If you have ever dealt with a diesel vehicle that is continually leaking fuel, won’t start or is difficult to start, runs roughly, or suffers from clogged fuel filters on a semi-permanent basis, chances are that the vehicle is running on fuel that contains substandard or degraded biodiesel. This article will discuss biodiesel in terms of what it is, and the problems and issues you as a diesel technician are likely to encounter on vehicles that run on substandard biodiesel, starting with this question-
In Australia, the Fuel Standard Determination 2003 defines biodiesel thus; “a diesel fuel that is obtained by a process of esterification of oil derived from plants or animals”. Put in another way, biodiesel is made through a process of converting animal fats or plant-based oils into a fuel that is suitable for use in existing diesel engines.
Most Australian biodiesel producers have either ceased production or closed up shop for various reasons, but the few producers that still manufacture biodiesel on commercial a scale generally deliver a product that meets both the ASTM (American Society for Testing and Materials) and CEN (European Committee for Standardisation) standards. As a result, fuel that is produced by these producers performs well, and should not cause issues in modern diesel engines.
However, the same cannot be said of biodiesel produced by many small-scale producers that include farmers and fleet operators that collectively, operate vehicle fleets that include diesel engines of almost any conceivable type and design. In these cases, the quality of the final product is often questionable as the result of manufacturing processes that can often be described as a hit-or-miss affair, at best, which brings us to-
While this article is not intended to be a treatise on the manufacture of biodiesel, it is important to understand at least the basics of the process in order to be able to diagnose some of the issues that poorly made biodiesel causes.
The image above shows a quantity of used cooking oil in a frying pan, which in Australia, forms the bulk of the feedstock used to produce biodiesel. In practice though, almost any brand of cooking oil can consist of a blend of up to five or six different vegetable oils, as well as a large percentage of water, in both liquid and dissolved states.
While water in oil does not present much of technical problem, the various oils in an oil blend all react differently to being heated, which can make the esterification and subsequent washing/drying processes of the fuel a haphazard affair, and especially if used oil from many different sources are used.
Nonetheless, the short version of how biodiesel fuel is produced generally follows the pattern described here-
In theory, what remains should be usable biodiesel, but in practice, it often isn’t, and it is here where the problems we as technicians often encounter start.
Creating usable biodiesel is a rather exact science, which means that many things can, and often do go wrong. However, since there are no DIY testing kits available and proper laboratory-grade testing takes both time and money, this article will explain the problems that come with using substandard biodiesel, and where possible, also the most effective remedies, starting with-
Poor combustion can have several causes if biodiesel is present in the fuel, with the most common being-
Poor injector spray pattern
This can be caused by the high viscosity of the biodiesel, which prevents proper atomisation of the fuel mix during injection. In some cases, the injectors’ orifices may become partially clogged, or deposits that affect the fuel spray pattern may form around the orifices. Note that deposits on injectors are a known feature of biodiesel that was derived from vegetable oils, and particularly on engines that operate at low loads for extended periods of time.
Hard starting
The composition of biodiesel feedstock plays a critical role in the fuels’ viscosity. For instance, biodiesel made from pure (100%) coconut oil will solidify at about 15 degrees Celsius. Thus, if a biodiesel blend contains a significant percentage of coconut-derived oil, the fuel’s viscosity may simply be too high to be pumpable, even though the ambient temperature may be well above freezing point.
Loss of engine power
Diesel fuels sold in Australia can contain up to five percent biodiesel, without the seller having to label the fuel as a blend of mineral-based diesel and biodiesel. This blend is known as “B5”, and in theory, it should not cause a noticeable decrease in engine power. However, there is no way of being absolutely sure that any given volume of diesel does not contain more than 5% biodiesel, which if it does, can cause a distinctly noticeable drop in engine power caused by poor combustion as a result of the increased viscosity of the fuel blend.
Suggested solutions
If poorly made biodiesel is suspected to be the cause of poor combustion, subjecting the injectors to a thorough ultra-sound cleaning might resolve the issue. Note that regular “fuel system cleaning additives” typically have no effect on biodiesel deposits. If an ultra-sound cleaning of the injectors is successful, hard starting, rough running, and power loss issues will generally go away as well.
Regular mineral diesel contains several kinds of waxes and varnishes that in time precipitate out of the fuel to form a waxy layer on the inside walls of the fuel tank and fuel lines, which does not generally cause a problem.
However, since biodiesel is an excellent solvent, even a 5% concentration of biodiesel in regular diesel will attack and dissolve this accumulated deposit of wax and varnish, resulting in clogged fuel filters, water traps, strainers in injection pumps, and even injectors. It should be noted though that it takes several years for a waxy layer to accumulate in a diesel fuel system, so if fuel filters clog regularly on a relatively new vehicle running any concentration of biodiesel, the cause is more likely to be related to the uncontrolled growth of algal and bacterial colonies in the fuel.
Although many species of microorganisms thrive in regular diesel under favourable conditions, biodiesel blends offer excellent conditions for such colonies to grow over a wide range of temperatures. In most cases, a colony of microorganisms has a semi-liquid, slimy appearance that may or may not smell bad, depending on the type of organisms present in the colony. If such a colony is allowed to grow uncontrolled, it can spread to fuel lines, water traps, and even high-pressure injection pumps. Note that clogged filters can also be caused by oxidation of the biodiesel, which causes wax crystals to form.
Suggested solution
Replacing clogged fuel filters usually provides only a temporary solution, because this issue has no single cause. In most cases, the best course of action is to remove the entire fuel system, and to have it chemically cleaned to remove all dissolved waxes and varnishes.
Note that while several effective algaecides are available to combat colonies of microorganisms, these remedies only kill the organisms; they do not remove the resulting sludge of dead and decomposing microorganisms. Thus, removing the sludge may require removal of the entire fuel system for the purpose of cleaning out the sludge. However, once the fuel system is clean, regular applications of a suitable algaecide will generally prevent a recurrence of the issue.
The most commonly used catalyst in biodiesel is caustic soda (sodium hydroxide), which is highly corrosive, and unless all the catalyst is removed from the biodiesel during the manufacturing process, the invariable result is catastrophic corrosion in the fuel system.
Suggested solution
If biodiesel is present in the fuel, corrosion is typically caused by the presence of catalyst and/or methanol in the fuel, excessive amounts of water, or excessive amounts of sulphur, and in some cases, all of the above. However, by the time corrosion is noticed, the injection pump and/or injectors may have already suffered damage that may or may not be repairable.
There is no single remedy for corrosion caused by poorly made biodiesel. As a rule, the best course of action to take is to remove the entire fuel system from the vehicle to check for corrosion, and to replace all damaged parts, components, or injection equipment.
Apart from being able to dissolve waxes and varnishes, biodiesel also dissolves and/or degrades certain elastomers used in the manufacture of fuel lines, some gaskets, and oil seals. Buna nitrile rubber is particularly vulnerable to attack by biodiesel, which means that in some cases, all the seals, gaskets, and flexible fuel lines in the vehicle must be replaced with biodiesel resistant (Viton or Teflon) seals, gaskets, and fuel lines.
Suggested solution
It should be noted that replacing all damaged or degraded seals, gaskets, and fuel lines is the only reliable remedy, since the damage to these items occurred at the molecular level. Reverting to using regular diesel will not magically repair damaged parts and components.
Poor spray patterns and/or poor combustion caused by substandard biodiesel can cause some liquid fuel to remain on the cylinder walls, from where it seeps down into the engine oil. Over time, this fuel seepage can dilute the engine oil to the point where oil pressure is compromised, which can obviously lead to engine failure.
Suggested solution
The best way to recognise oil dilution is to monitor the oil level. Since a steady increase in the oil level is proof that fuel is finding its way into the oil, corrective action must be taken without delay. Note that corrective action can include anything from replacing the fuel, to chemically cleaning out the entire fuel system.
As stated elsewhere, a proper analysis of biodiesel and biodiesel blends requires specialised equipment, and advanced testing techniques that cost both time and lots of money. However, since many, if not most issues caused by biodiesel can be traced back to its viscosity a simple test may help to confirm viscosity of the fuel as the root of the problem. Here is how to-
Test for viscosity
Obtain a sample (about 250 ml or so) of fuel from the affected vehicle, as well as a similar sample from a supply of diesel that is known to be good. Place both samples in separate glass containers (two tall drinking glasses work well), and place both samples in a fridge.
If viscosity is a problem, the viscosity of the bad fuel will increase as the temperature drops. Thus, cool both samples down and simply compare their relative viscosities several times as they cool down to about 10 degrees Celsius. Note that while this test is highly subjective, a difference in the viscosity of the bad fuel is proof that the biodiesel in the fuel does not comply with accepted quality standards.
Note that any turbidity or cloudiness in the cooled fuel sample could indicate the presence of wax crystals as a result of incomplete conversion of the fats in the feedstock, or the presence of excessive amounts of water. See the test below.
Test for the presence of water and/or methanol
Note that although this test requires the use of a scale that can measure in grams, investing in such a scale can save you a lot of time and money.
If you have such a scale, obtain a fuel sample of about 100 grams or so from the affected vehicle. Place the fuel in a stainless steel cup, and weigh the fuel sample with the cup. Place the cup on a heat source, and bring the fuel to a gentle boil for about five minutes.
Let the fuel cool down, and weigh the cup with the fuel again. If the sample had lost some weight, no matter how little, this is clear proof some water and/or methanol had boiled off, which in turn, is unambiguous proof that the fuel in the affected vehicle does not comply with accepted quality standards.
It should be borne in mind that while backyard-produced biodiesel cause the most issues, branded diesel/biodiesel blends sold by reputable manufacturers are not entirely immune to oxidation and other errors in fuel handling and storage that degrade the fuel. Therefore, even branded diesel fuel blends can also cause most, if not all of the problems associated with biodiesel produced in backyard sheds, so use your best judgment when you are investigating fuel related issues on diesel vehicles because biodiesel is not always to blame.
