Questions and answers (FAQ) about the fuel check

Fuels degrade with increasing storage time. This degradation (aging) is a natural process that occurs slowly under favorable storage conditions. There are some factors that can accelerate the aging of fuels during storage. The most important influencing factors include daylight (UV radiation), storage temperature (heat) and ambient air (oxygen, O2). Another important factor is due to the use of copper lines (introduction of metal ions into the fuel) for fuel supply. In addition, the choice of fuel has an influence, as there are fuels that are less stable in storage than others.

The higher the ambient temperature, the faster aging processes can occur. In (almost) all emergency power systems with a day tank, the emergency power system engine is kept warm for a quick start with a cooling water temperature of up to 47 °C. The day tank is usually kept at the same temperature as the engine. The day tank is usually installed in the same room as the emergency power system and is exposed to increased temperatures due to the waste heat from the engine, which leads to faster fuel aging. If the main tank is installed in a separate, well thermally insulated room, often it is also located underground outside the building, the fuel aging process is slower there.
Another factor is copper fuel supply lines between the tank and the engine that may be installed in PSUs. Non-ferrous metals have a catalytic effect and cause the fuel to age more quickly.
Engine manufacturers for emergency power systems usually recommend the use of diesel fuel for system operation. However, diesel is only available in a blend with up to 7% biodiesel. This blend is designed for short-term consumption in transportation, but not for long-term storage. As the storage period of this blend increases, the risk of fuel-related malfunctions due to aging processes and possible microbiological infestation of the fuel increases.

When stored in tanks in enclosed spaces, an influx of oxygen from the ambient air is usually relevant. From a chemical point of view, this produces free radicals over time that can react with oxygen from air and change the molecular structure of the fuel (Oxidation). This is referred to as degradation of the fuel. The introduction of heat or metal ions from copper lines into the fuel catalyzes, i.e. accelerates, the aging process. In addition, oxidation can also lead to the formation of acids in the fuel, which in turn can lead to corrosion of fuel-carrying components of the engine system.

In the case of diesel with a biodiesel content (up to 7% biodiesel is commonly added to mineral oil-based diesel), external influences can also cause polymerization of the fuel. Molecular structures and the properties of the fuel would change during polymerization. Above a certain molecular size, the polymers precipitate out of the fuel and form sticky deposits at the bottom of the tank.

A similar picture is seen with microbiological infestation of biodiesel. This is commonly referred to as “diesel plague” but, strictly speaking, is not a typical aging process. Microbes from the environment (and possibly also from the bio-content of the diesel fuel) enter the fuel, multiply and form a biofilm that settles between a water phase and the fuel phase.

The consequences of aging / degradation of a fuel can be severe. The engine will still start and run for a while. However, once the fuel pump delivers deposits and biofilms to the engine, fuel filters and injectors can become blocked, and deposits can build up in fuel lines causing malfunctions and even engine failure. Depending on the extent of the damage, cleaning or replacing the affected components of the engine can incur considerable costs.

There is no general rule of thumb for the minimum shelf life of fuels in emergency power systems because the influencing factors vary widely. For example, the quality of the fuel batch, the type of fuel (admixture of biodiesel, additives, etc.), the storage temperature, non-ferrous metals used in the plant and the formation of water all play a role. Experience from the quality testing of fuels in emergency power systems shows that the usability of one fuel can be critical after only 2 years of storage, while another fuel has already been stored in the tank for 30 years and is stable. Only an analytical fuel check could give certainty about the further usability.

If low-sulfur heating oil is used in diesel engine network replacement systems, the addition of special additives is recommended in order to optimize the performance of the engine as well as the operational reliability and longevity of the system. When selecting a suitable additive, it is important to ensure that it fulfills a number of important functions. More on the subject of additives

Engine manufacturers generally require the use of diesel fuel in accordance with DIN EN 590 for the operation of their emergency power systems. To comply with the Biofuel Quota Act, up to 7% biodiesel is now commonly blended with diesel fuel. With its special properties, this fuel quality is designed for the transport sector and for use within 90 days, but not for long-term storage. In the case of biogenic blends, longer storage periods for diesel stocks increase the risk of fuel-related malfunctions of the emergency power system due to degradation and microbiological infestation.

Alternatively, it is also possible to use low-sulfur heating oil according to DIN 51603-1. It has the same physicochemical properties as diesel but does not contain any biodiesel. Since emergency power systems are stationary engines, the use of heating oil is permitted by law. Another advantage of using heating oil is the lower cost due to the lower energy tax of 6.14 cents per kilogram compared to 47.04 cents per liter for diesel fuel. Before deciding to use heating oil, it is essential to check whether the manufacturer of the system has given approval for its use.

For emergency power systems with fuel stocks of less than 1,000 to 2,000 liters, a meaningful fuel check is not recommended for economic reasons. In these cases, it is more advantageous to replace the fuel in good time so that it can still be recycled/used elsewhere if necessary.

In order to maximize the usability of fuel stocks as far as possible, a switch to paraffinic fuels could be suitable, depending on the application. These are somewhat more expensive to purchase but are characterized with greater storage stability.

Customers can choose whether they want to carry out the fuel check themselves or have it done by Tec4Fuels or a contracted company. If you want to take a sample in your fuel tank yourself, Tec4Fuels will provide you with a sampling kit. Detailed instructions (link to instructions) on how to proceed and how to send the sample to an analysis laboratory will be provided. The sample is taken from the day tank. If after the analysis it turns out that the fuel in the day tank is not usable or only in critical state, Tec4Fuels recommends to take an additional sample from the main tank and have it analyzed. If the sample from the day tank is still in order, an analysis of the contents of the main tank is not necessary.

The fuel analyses prescribed in the fuel standards DIN EN 590 and DIN 51603 are suitable for ensuring quality when selling to customers. However, the fuel analyses prescribed in the standards do not allow reliable statements to be made about the long-term shelf life of a fuel.

Tec4Fuels has therefore selected a number of additional fuel parameters that are relevant for long-term storage and has them analyzed for fuel quality testing by accredited analytical laboratories using standardized procedures. Based on these parameters, such as oxidation stability, valid statements can be made about the quality and usability of a fuel.

Yes, already today, there are practicable solutions available for this. For example, switching to climate-friendly paraffinic fuels made from residual and waste materials could be a way to reduce fuel-related CO₂ emissions by up to 90 %.

To achieve this, certain preconditions must be taken into account. There are various paraffinic fuels and fuel blends that combine the important properties of climate protection and long-term storage stability. Depending on the type and size of the plant and the objectives, one or different fuels could be considered to achieve an optimum result. It is also important to check whether the engine manufacturers have approved the use of paraffinic fuels for the grid replacement system(s), in question. If no approval is available, there are solutions for this as well.

With comprehensive fuel and plant know-how, Tec4Fuels can assist in identifying the optimum fuel for the application in question, ensuring compatibility of fuel and plant, and setting up customized supply logistics.