Mercedes Mullins
There are several factors that can cause diesel fuel to turn brown. One of the most common causes is microbial contamination, often referred to as the diesel bug. This contamination can lead to the growth of bacteria, algae, or other microorganisms in the fuel, which can turn it brown or black. Additionally, the presence of rust or water in the fuel can also contribute to discolouration. Preventing diesel fuel degradation involves treating it with stabilizers, removing water from the tank, and using biocides to kill any microbial contamination early on.
| Characteristics | Values |
|---|---|
| High molecular weight hydrocarbons | As the molecular weight increases, the compounds become heavier and more complex, leading to a darker color |
| Lighter hydrocarbons | Lighter hydrocarbons like methane (#1/#2 diesel fuel) are colorless or a much lighter color |
| Polycyclic aromatic hydrocarbons (PAHs) | PAHs absorb light effectively, particularly in ultraviolet and visible regions, making the substance appear black or dark brown |
| Water in the storage tank | Water in the tank can lead to microbial contamination and the growth of the "diesel bug," which can turn the fuel brown |
| Sediment content | Higher than normal sediment content in fuel samples can indicate degradation |
| Coating on surfaces | Slime or abnormal coatings on tank walls can be a sign of fuel degradation |
| Biodiesel | Biodiesel is hygroscopic and attracts water, leading to contamination and a potential source of the "diesel bug" |
| Rust | Rust from metal tanks can mix with water and bacteria to form a brown substance |
| Algae | Algae can grow in diesel fuel, causing brown or black discoloration |
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What You'll Learn
The presence of the 'diesel bug'
The presence of the diesel bug can cause diesel fuel to turn brown. The diesel bug is a microbial contamination that thrives in the presence of water and biodiesel. Biodiesel is hygroscopic, meaning it attracts and holds water more than other types of fuel. This creates an ideal environment for the diesel bug to grow and multiply rapidly. Within 20 minutes, the diesel bug can double in size, forming a thick biomass that clogs filters, corrodes fuel storage tanks, and damages engines.
The diesel bug can also produce a slime layer between the water and fuel, which may appear dark brown or black in colour. This slime can emit a foul odour, resembling rotten eggs. To prevent the growth of the diesel bug, it is crucial to ensure that no water enters the fuel storage tank and to maintain good housekeeping practices.
In addition to the diesel bug, other microbial contaminants can cause discolouration in diesel fuel. For example, algae can grow in fuel tanks, resulting in a reddish-brown tint and injector issues. To address this, it is recommended to treat the fuel with a biocide and change the tractor fuel filter after the engine has run for a while.
Another potential cause of brown discolouration in diesel fuel is rust. Rust particles can flake off from metal tanks and mix with water and bacteria to form a substance called "mother." Inspecting the fuel filter and tank can help identify the presence of rust or other contaminants.
To prevent and treat microbial contamination in diesel fuel, various products are available, such as additives, biocides, and fuel polishing services. These treatments can help break down bacteria and maintain the fuel system, ensuring the smooth operation and longevity of vehicles.
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Rust from metal tanks
Diesel fuel is susceptible to contamination, especially when it is stored for extended periods. Rust can form in metal tanks, and the rust particles can mix with the fuel, resulting in discolouration. This can lead to issues with injectors and other engine components. To address this, it is recommended to replace the fuel filter, inspect the tank, and consider using additives or biocides to treat the fuel and remove contaminants.
In addition to rust, the presence of water in the fuel tank can also contribute to the growth of bacteria and algae, which can further discolour the diesel. This is more common in biodiesel, which tends to contain up to 7% biodiesel—a substance that attracts and holds water. The combination of water and biodiesel creates an ideal environment for the diesel bug, a type of microbial contamination that can multiply rapidly and cause significant problems in the engine or tank.
To prevent and address these issues, it is crucial to maintain good housekeeping practices. This includes regularly inspecting and cleaning fuel tanks, using fuel additives or biocides to treat contamination, and ensuring that the fuel storage tank has a high-quality filter system installed. By taking proactive measures, you can extend the lifespan of your fuel and avoid costly repairs caused by contaminated diesel.
It is worth noting that the age and source of the diesel fuel can also play a role in discolouration. Older fuel or fuel sourced from different locations may be more prone to contamination and discolouration. Therefore, it is advisable to pay attention to the appearance of the fuel and take preventive measures to maintain its quality.
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Biodiesel attracting water
The bane of diesel fuel is the "diesel bug", a microbial contamination that thrives in the layer between water and fuel. The diesel bug can clog filters, corrode fuel storage tanks, and wreck engines. It can also produce a dark brown or black biomass that can coat the inside of tanks and cause havoc in engines.
Biodiesel is a common component of diesel fuel, often making up to 7% of its content. Biodiesel is hygroscopic, meaning it attracts water more than other fuels. This makes biodiesel more susceptible to the diesel bug. When the industry used petrochemical diesel instead of biodiesel, there were fewer problems as it does not attract water in the same way.
The key to avoiding the diesel bug is good housekeeping. This includes regularly cleaning and maintaining fuel storage tanks, as well as using biocides to kill any microbial contamination early on. It is also important to prevent water from getting into fuel storage tanks and to use high-quality fuel in vehicles.
In addition to the diesel bug, water can also have negative effects on biodiesel production. The presence of water during the transesterification of fats and vegetable oils for biodiesel production can cause soap formation, consume the catalyst, and reduce catalyst efficiency, resulting in a low conversion of methyl esters. However, some studies have shown that the presence of water at certain amounts can enhance the formation of methyl esters.
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Algae build-up
The presence of algae can cause operational issues in engines and fuel systems. It can clog filters, corrode fuel tanks, and lead to engine problems. Reddish-brown particles in diesel fuel are often indicative of algae growth. To address this issue, it is recommended to treat the fuel with a biocide or algaecide, following the manufacturer's instructions. Preventative measures include using fuel stabilizers, removing water from the tank, and employing biocides to kill microbial contamination early on.
In addition to algae, other factors can contribute to the discoloration of diesel fuel. For example, high molecular weight hydrocarbons can lead to darker-colored fuels. Tar and asphalt, which contain high concentrations of polycyclic aromatic hydrocarbons (PAHs), are large, multiple-ring aromatic compounds that absorb light effectively, resulting in a black or dark brown appearance.
It is important to regularly inspect and maintain fuel storage tanks to prevent and address issues like algae build-up. Proper housekeeping, including cleaning and maintenance, can help prevent diesel bug growth and ensure the fuel remains in a usable state.
If you suspect algae build-up in your diesel fuel, it is recommended to seek professional assistance. There are vendors that offer services to treat and flush fuel tanks, as well as chemical cleaning options for removing algae and other contaminants.
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Complexity of hydrocarbon compounds
Diesel fuel is a complex mixture of hydrocarbon molecules, primarily consisting of aliphatic, olefinic, naphthenic, and aromatic hydrocarbons. These hydrocarbons are derived from the distillation of crude oil, with carbon numbers predominantly ranging from C9 to C20. The complexity of these compounds arises from their molecular weight and structure, which can include branched-chain configurations.
The molecular weight of the hydrocarbon compounds in diesel fuel contributes significantly to their complexity. As the molecular weight increases, the compounds become heavier and more complex. This increase in complexity leads to a darker colour in the fuel. Lighter hydrocarbons, such as methane, have lower molecular weights and are therefore colourless or much lighter in colour.
The distillation process plays a crucial role in the formation of these complex compounds. Diesel fuel is typically produced through fractional distillation, which involves separating the components of crude oil based on their boiling points. The resulting diesel fuel consists of hydrocarbons with boiling points ranging from approximately 163°C to 357°C. However, this range can vary slightly depending on the specific type of diesel fuel.
The composition of diesel fuel can be further enhanced by blending it with other refinery streams. For example, conversion refineries may use components from cracking processes to increase diesel fuel production. Additionally, kerosene may be added to modify the viscosity of the fuel. These blending processes contribute to the overall complexity of the hydrocarbon compounds in diesel fuel.
The presence of certain heteroatoms, such as sulfur, nitrogen, and oxygen, can also influence the complexity of diesel fuel. When these heteroatoms are bound into molecular structures with carbon and hydrogen, they create non-hydrocarbon compounds within the fuel. Examples of these non-hydrocarbon compounds include dibenzothiophene and carbazole. While these compounds add complexity to the fuel, they are not characterised as hydrocarbons themselves.
The complexity of hydrocarbon compounds in diesel fuel has a significant impact on its performance and emissions characteristics. The specific types and ratios of hydrocarbons used in diesel fuel, such as alkanes, cycloalkanes, and aromatics, can affect engine combustion, emissions, power, and fuel economy. Therefore, the complexity of these compounds is a critical aspect of diesel fuel's functionality and environmental impact.
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Frequently asked questions
Brown diesel fuel is likely caused by rust in your tank. It could also be a result of microbial contamination, which can be prevented by using biocides.
Diesel fuel can also be white, blueish-white, black, or dark brown. White or blueish-white diesel fuel can indicate a lack of power or a clogged fuel filter. Black or dark brown fuel is often a result of too much fuel being injected in relation to the air available for combustion.
If your diesel fuel is brown, you should take it to a local vendor who can run your fuel through a system that will treat it and then flush the tanks. Alternatively, you can remove the tanks and send them to a local radiator shop for a chemical clean.
To prevent your diesel fuel from turning brown, you should treat it with stabilizers, remove free water phases from the tank bottom, and use biocides to prevent microbial contamination.
