An Editorial by dieselmann
Volume 12; July 01: Fuel Additives
It has been suggested that I write an article on the subject of fuel additives. I have been asked about fuel additives on several occasions, particularly how and when they should be used, as well as which brands I recommend. I could go into specifics on the properties of diesel fuel, but that would make this artcle unecessarily long. Instead, I will try to stay on the topic of fuel additives themselves. If you are interested in the properties of diesel fuel, I would suggest visiting Chevron's diesel fuels technical review.
There are a variety of fuel additives, many of which combine different properties to correct problems with the fuel or in fuel systems. Generally, these additives are used either to increase the performance of the engine, protect the fuel system from damage, or to minimize degradation or contamination of the fuel.
Performance additives attempt to make the fuel system work more efficiently, or the fuel burn more completely, which would produce more power from the same amount of fuel. Cetane is a number representing how readily diesel fuel ignites once it's injected into the engine. The higher the number, the more easily the heat from compression will cause autoignition. Also, the higher the cetane number, the more easily the engine will start when cold and less white smoke is produced at cold start. A higher cetane rating can also reduce combustion noise.
Detergents perform as you would expect, either preventing residue build up or removing deposits from the fuel system. Usually fuel system deposits are caused by lubricants in the fuel, but may also be from engine oil. These deposits can form on the interior of injection pumps or injectors, which would prevent the parts from moving freely. This would result in hard starts, missfire or rough running, stalls, higher than normal idle or may even cause the engine to continue to run after the ignition is turned off. Carbon may also form on the injector nozzel, which would affect the fuel spray pattern. This would result in incomplete burning of the fuel, low power, smoke and rough running.
Diesel fuel lubricity additives help to coat fuel system components, which provides a barrier between moving parts. In systems with particularly close tolerances, anything that reduces the lubrictating properties of the fuel is a potential for damage. Water that is absorbed into the fuel, alcohol from some fuel additives, or gasoline mistakenly added to the tank or used to kill algae can all cause the lubricity of the fuel to decrease, which can potentially result in damage. Lubricity additives can help to reduce or prevent damage to the fuel system in cases of contamination. When fuel system maintenance is to be performed, a lubricity conditioner would be beneficial in preventing damage which could result from dry cranking or during the first start.
Catalysts are primarily used to suppress black smoke emissions. Usually, they are in the form of organometalic compounds or are metallic based. The catalystic compound causes the fuel injected into the cylinders to burn more completely, which reduces the amount of particulate emissions (soot) being exhausted from the engine.
Diesel fuel has an inherant problem of being hygroscopic, which means it readily absorbs moisture from the air. Other than the obvious problem of being non-combustable and the potential for freezing and restricting fuel delivery, water also causes corrosion of fuel system components and reduces the lubricity of the fuel, both of which result in wear. Many fuel additives contain chemicals that disperse moisture in the fuel. If the moisture is dispersed, it cannot concentrate in one area and cause a restriction in fuel delivery if it freezes. In addition, being dispersed in the fuel allows the moisture to be carried to the water separator where it can be removed from the fuel.
In cold conditions two problems may occur. First, any water present in the fuel system can freeze and interupt fuel delivery. De-icing or freeze depressants lower the freezing point of the water to prevent this from happening. The second problem is know as gelling, which is what happens when wax crystals form in the fuel. This effects how well the fuel flows and can reduce fuel delivery to the point of preventing the engine from starting. Pour-point depressants lower the temperature at which the fuel will flow and wax dispersants keep any crystals evenly distributed throughout the fuel. To be effective, pour-point depressants and wax dispersants must be added before gelling occurs.
Another problem related to moisture in the fuel is organic contamination. Moisture in the air contains micro-organisms. When moisture is absorbed by diesel fuel, and the water is allowed to collect or concentrate, these micro-organisims can multiply to the point where problems may occur. Usually this problem only occurs where fuel is allowed to sit around for prolonged periods. But once in truck, algae can plug fuel filters and passages in the injectors or injection pump. In some cases fungus or slime will form inside areas of the fuel system and produce an oganic acid which will corrode fuel system components. A biocide should be used in storage tanks to prevent the fuel from becoming contaminated, and can be used if contamination is spread to vehicle tanks.
Corrosion inhibitors protect the fuel system components from rust formation by coating the metal parts. Fuel stablizers maintain the integraty of the fuel to prevent the formation of deposits in the fuel system. Anti-oxidants reduce the reaction of oxigen with the fuel to help stabilize the fuel and prevent rust.
Fuel additives can be used to address specific problems with certain fuels, or as a preventative measure against potential problems. They should not be used to correct mechanical problems. There has been speculation that in some areas the actual cetane at the pump may be lower than the federal minimum rating of 40 (the PowerStroke was designed to run on fuel with a cetane rating of 40 or higher). If you experience smoke concerns with no apparent lack of power, hesitation or hard cold starting, the cetane of your fuel may be lower than it should be.
Sometimes, in order to meet certain local emissions requirments, the fuel is processed in such a way that other properties of the fuel suffer. A case in point would be when California required a reduction in sulfur content as well as aromatics in diesel fuel in the early 90's. While reducing sulfur in diesel fuel in itself does not reduce lubricity of the fuel, the method that was used to reduce the sulfur did, which resulted in a rash of injection pump failures at that time. Problems such as this could have be prevented with fuel additives. Ford even released a TSB recommending the use of Stanadyne Performance Formula to correct a stall at stops in the 6.9 and 7.3 IDI diesels if no contamination of the fuel or mechanical problems with the truck were found.
I recommend the use of fuel additives on a regular basis if you believe the fuel you are receiving is of poor quality, specifically one that raises cetane and lubricity, has detergent, anti-corrosion and water dispersants. Also, I recommend using them at each fill-up during wet weather or in winter when problems would be most likely to occur, particularly cetane and lubricity increasers, water and wax dispersants, and freeze and pour-point depressants. A Special Service Message from Ford recommends the use of Stanadyne Performance again for a loss of power on the 99 and newer trucks due to ice balls clogging the fuel tank pick-up screen in cold climates.
Under normal conditions I recommend using a fuel additive for preventative maintenance of the fuel system. Use an additive that increases lubricity, cleans the fuel system and reduces corrosion about every third tank full.
If you have your own fuel storage, then a biocide and fuel stabilizer should be used to prevent contamination and degradation.
I recommend using a fuel additive made by a fuel injection or fuel systems manufacturer, such as Stanadyne, Lucas or Racor. Additives made by lubricant manufacturers, such as Amsoil, are acceptable too, providing they do not contain alcohol. However, keep in mind some cetane boosters can cause injector cackle to become more pronounced as it may affect the thermal stability of the fuel. For this reason, an additive that combines several of the above properties would be more benifitial than one that provides only one.
My recommendations
Save on gas with Ford truck bed covers from AmericanTrucks.
Charles David Ledger; dieselmann©1999
Back to Blowin' Smoke
©
©