Diesel fuel examination

Diesel Fuel Charter Requirements

The cetane number is a characteristic of the compression ignition of the fuel. An increase in the cetane number reduces the cranking time of the engine crankshaft before starting, and also significantly reduces emissions of harmful substances, fuel consumption and noise. The level of noise, emitted smoke and engine power depend on this parameter. The range of cetane number indicators acceptable for universal use is from 40 to 50. In fact, this figure reflects the duration of the ignition delay. However, if this figure exceeds the 60 mark, such fuel will not affect power in any way.

If a few decades ago the use of diesel fuel for passenger cars was not possible, today the situation has changed. More and more vehicle owners are switching to using this product due to its availability and efficiency. But its quality is an invariable criterion, from which it is worth starting from when buying.

The key characteristic of diesel fuel is its flammability level. It determines how long the fuel will take from entering the cylinder until it is immediately ignited. The shorter this period of time, the higher the cetane number will be. Its high value also improves engine performance, contributes to more correct and safe operation of the mechanism. Why is this parameter so important in determining quality?

The cetane index can be used to track the chemical composition. The flammability level will directly depend on the hydrocarbon composition of the fuel. Paraffin-based formulations burn best, aromatic compounds worst of all. Therefore, in this proportion, it is necessary to track the amount of aromatic hydrocarbons, since the quality of diesel fuel is determined by them. So, if the indicator is less than 40, this will guarantee additional load on the engine and work in a more severe mode. Regular refueling of such fuel will negatively affect the condition of the engine, accelerating its wear.

The cetane index is the cetane number of a fuel and is calculated based on measurements of the properties of the fuel. The cetane number is determined on a test engine and reflects the effect of fuel additives that improve the cetane number of the fuel.

The cetane index and cetane number affect vehicle performance in different ways. Therefore, in order to avoid overdosing of fuel additives, it is necessary to keep the difference between the cetane index and cetane number as small as possible.

Density and kinematic viscosity. Changes in the density (and kinematic viscosity) of the fuel lead to changes in engine power and therefore to changes in engine emissions and fuel consumption. To optimize engine performance and exhaust emissions, both the minimum and maximum density limits must be defined within a fairly narrow range.

The reduced density will reduce particulate matter emissions from all diesel vehicles and NOx emissions from heavily loaded vehicles. However, a lower density will also increase fuel consumption and reduce engine power. Variations in the kinematic viscosity of the fuel (a decrease in density usually leads to a decrease in viscosity) can increase the influence of density on power (but not necessarily on fuel consumption), especially in combination with fuel injection pumps.

Production diesel engines are set to a certain standard density, which determines the amount of fuel injected. Fuel injection volume is a control parameter for exhaust gas treatment systems such as an exhaust gas recirculation (EGR) system. Consequently, changes in fuel density lead to non-optimal levels of RVG for a given load and a given speed in comparison with those set in the vehicle's program and, as a consequence, affect the characteristics of exhaust gases.

Fuel delivery and injection regulation also depend on the viscosity of the fuel. High viscosity can reduce the rate of fuel consumption, resulting in inadequate fuel delivery. Very high viscosity of the fuel can deform the pump. Low viscosity, on the other hand, will increase leaks from the pump elements and in the worst case (low viscosity plus high temperature) can lead to a complete loss of fuel due to leakage. Since viscosity is influenced by ambient temperature, it is important to keep the range between the minimum and maximum viscosity limit as small as possible in order to optimize engine performance.

The fuel system installed on diesel units of any purpose has a specific device. It includes a tank, a set of fuel line pumps and special cleaning filters. The latter are of several types, depending on their purpose. So, coarse filters are necessary to retain mechanical particles, the size of which does not exceed 60 microns. Fine filters are responsible for the retention of solid elements, whose parameters range from 2 to 5 microns.

The quality of diesel fuel passing through the power system is influenced by the mass of its key parameters: low-temperature indicators, the level of viscosity, the presence of water and naphthenic acids in the composition.

The most "problematic" parameter of all of the above is viscosity. The larger it is, the more difficult it is to pump fuel. The problem is especially urgent in winter. In order to neutralize the negative effect of frost on the fuel condition, the supply of the booster pump, which takes over the main load, exceeds the required supply for optimal operation of the diesel engine by 5 times.

The boiling point characterizes the completeness of the evaporation of diesel fuel in the engine. If it is too high, the fuel will not be able to completely evaporate, and as a result, it will settle on the inside of the entire combustion chamber. This, in turn, will lead to accelerated wear of the main parts of the system.

Flash point is the lowest temperature value at which vapors can flash in the presence of an open fire source. In this case, a stable combustion process should not occur.

Sulfur is a natural component of crude oil. If sulfur is not removed during the refining process, it will contaminate vehicle fuels. Diesel sulfur determines the amount of fine particulate matter (PM) emissions in exhaust gases due to the formation of sulfates, both in the engine and later in the atmosphere. Sulfur can lead to corrosion and wear on engine systems. Moreover, the efficiency of some exhaust gas cleaning systems decreases with increasing sulfur concentration in the fuel, while other systems completely fail due to sulfur poisoning. The impact of sulfur on particulate matter emissions is widely recognized and considered significant.

Particulate filters. Continuous Regeneration Diesel Particulate Filters (DPFSPs) and Catalytic Diesel Particulate Filters (DPFs) are two approaches to regenerating Diesel Particulate Filters (DPFs). The DPFTPR regenerates the filter by continuously generating NO ₂ from the NO emitted from the engine on a diesel oxidation catalyst placed in front of the DPFTPF. The DPFC regenerates the DPFC using a catalytic coating on the DPFC cell to promote oxidation of the collected PM using the oxygen present in the diesel exhaust.

Aromatic hydrocarbons are fuel molecules that contain at least one benzene ring. The aromatic hydrocarbon content of diesel fuel affects the combustion temperature and therefore NOx emissions during combustion. Polyaromatic hydrocarbons in fuels affect particulate matter formation and polyaromatic hydrocarbon (PAH) emissions from a diesel engine.

Fractional composition. The diesel fuel fractional curve shows the amount of fuel that will boil off at a given temperature. The light fractions contained in the fuel affect the ease of starting. Too much heavy ends will result in coking and increased emissions of soot, smoke and particulate matter. The resource consumption, wear of parts, burnout of piston rings and optimal start of the vehicle depend on it.

To achieve optimal performance of a diesel engine, the formation of a fuel-air mixture in the cylinder is of fundamental importance. For him, not only the quality of the atomization is important, but also the speed of its evaporation. The evaporation rate is determined by the fractional composition. This indicator is of particular importance for high-speed diesel engines. However, a high concentration of light ends in fuel has a negative impact on combustion quality.

Fuel with a high concentration of heavy fractions will evaporate much more slowly and not completely burn, thereby clogging the engine. Therefore, for a high level of operation of equipment operating on diesel fuel, you need high-quality raw materials with an average fractional composition. It should not contain light gasoline compounds that add additional weight to the engine. But the minimum concentration of heavy fractions, which do not completely burn out, is also important. As the ongoing studies clearly demonstrate, high-quality diesel fuel should contain the maximum number of fractions obtained by distillation in the temperature range from 250 to 350 degrees Celsius.

Low temperature fluidity. Diesel fuel can have a high content (up to 20%) of paraffins, which have limited solubility in the fuel and, if cooled sufficiently, will separate from solution as solid paraffin. Consequently, sufficient fluidity at low temperatures is one of the main characteristics of diesel fuel. Low temperature fluidity is usually determined by the fractional composition of the fuel, the hydrocarbon composition (the content of paraffins, naphthenes, aromatic hydrocarbons) and the use of fuel additives.

The technical requirements for the low temperature fluidity of diesel fuel should be set in accordance with the seasonal and climatic needs of the region in which the fuel is used. Paraffin wax in automotive fuel systems is a potential source of operational problems. Consequently, the low temperature properties of diesel fuels are determined by tests associated with the formation of paraffin:

• cloud point - the temperature at which the heaviest paraffins begin to precipitate and form wax crystals: the fuel becomes "cloudy";
• Filterability Limit Temperature — The lowest temperature at which fuel can pass through a filter during a standardized filtration test;
• pour point - this indicator is used in the US and Canadian markets.

One of the important characteristics when using diesel fuel is its ability to withstand low temperatures and at the same time maintain its mobility. These properties are due to the presence of paraffins in the fuel, which crystallize with decreasing temperature limits. Its properties depend on the degree of turbidity and solidification.

It is customary to denote the cloud point when the fuel changes so that a solid phase is formed together with the liquid phase. Then it becomes more turbid, but the mobility is still preserved due to the fact that the crystals formed in it are very small. The pour point is the moment when it loses its mobility.

Turbidity, despite maintaining fluidity, can still lead to malfunctions when starting the engine in the fuel supply. To avoid this, the ambient air must be warmer than the cloud point during warming up and starting.

After turbidity, solidification may occur, which is expressed in the fact that the fuel takes the form of a gelatinous mass, ceases to be fluid. The engine will operate normally, provided that the surrounding atmosphere is warmer than the solidification of the diesel fuel itself by about 8-12 degrees.

Foaming. Diesel fuel tends to foam when filling the fuel tank, which slows down this process and creates the risk of overfilling. Antifoam additives are sometimes added to diesel fuels, often as part of a multipurpose additive package, to speed up and fill a vehicle's tanks more quickly. Their use also reduces the likelihood of fuel spillage on the ground. Organosilicon surfactants are effective in inhibiting foaming tendency in diesel fuels. It is important that the selected antifoam additive does not create any problems for the long term reliability of the exhaust gas aftertreatment systems.

Esters of vegetable oils (VERs) are increasingly being used as a supplemental diesel resource or as a substitute for diesel fuel. This is due to the efforts of some countries to use agricultural products or reduce dependence on imports of petroleum products. There is evidence of a positive environmental impact of these products. However, there are doubts about the use of these esters in high quality diesel fuels.

The technical advantages of methyl ester are mainly in the fact that they provide lubrication to fuel equipment, which is degraded by the removal of sulfur from diesel fuel, and reduces particulate matter emissions from the exhaust gases. The disadvantages of methyl esters are as follows:

• they require special precautions at low temperatures to avoid excessive viscosity growth and loss of fluidity. Fuel additives may be required to correct these problems;
• since these esters are hygroscopic, special precautions are required to prevent increased water content and subsequent risk of corrosion;
• the tendency to form deposits increases, therefore it is strongly recommended to treat diesel fuel with detergents;
• gaskets and composites in the fuel system are exposed to methyl esters if not matched to the fuel.

Considering the technical effect of ethers, their content is limited to 5%. The use of esters in higher concentrations requires the adaptation of engines to this type of fuel.

Fuel injector cleanliness. The stable operation of the engine depends on the quality of the fuel injector. If contaminated, there will be increased noise, smoke and emissions.

The tip of the fuel injector is subjected to very severe stresses, since it is located directly in the combustion zone, both in prechamber engines and in direct injection engines. Solid combustion products form deposits on the tip of the fuel injector, which significantly affects the operation of the injector. In prechamber engines, sediment products partially block the uninterrupted supply of fuel at partial load, and combustion may become more unstable. Likewise, in direct injection engines, partial or complete blockage of one of the fine spray holes will interfere with fuel spray and engine operation.

In the case of pre-combustion engines, coking is inevitable due to the type of fuel injector used and this must be taken into account when choosing a fuel injector. However, the level of coking also depends on the quality of the fuel. Fuel injectors on direct injection engines are inherently more resistant to coking, but poor fuel quality can eventually lead to a blockage in the nozzle orifice.

The solution to this problem must be sought in the use of detergents in the fuel. Large doses of these additives can partially wash off an already heavily coked fuel injector, while smaller doses can maintain an acceptable level of injector cleanliness. Many fuel distributors include such fuel additives in their commercial diesel fuel. Fuel injector cleanliness will become even more important in the not too distant future as high pressure injection systems are increasingly used in both heavy duty and light duty direct injection engines.

Lubricity. Diesel pumps, which do not have an external lubrication system, are designed for the lubricating properties of the diesel itself. Refining processes to remove sulfur from diesel fuels simultaneously reduce the amount of fuel components that provide natural lubrication. Insufficient lubricity can lead to increased exhaust emissions, increased wear of the fuel pump and, in some cases, accidental breakdowns.

Diesel fuel EURO

Diesel fuel Euro GOST is a type of diesel fuel produced by refineries according to the European quality standard. It excludes the division into seasonal species, varieties and brands adopted in 1983. According to European product standardization, such fuel is differentiated according to the following criteria:

• Classes: 0 to 4;
• Grades: A, B, C, D, E, F;
• Types: I, II, III.

Each of these groups has its own subsections, that is, a particular type of diesel fuel has its own form. This classification is designed to facilitate the search for the optimal product on the market. Symbols of each type are indicated in the accompanying documentation. They are decrypted as follows:

• "Class" is an indicator of the temperature value at which the diesel fuel starts to darken;
• "View" refers to the percentage of sulfur concentration in the total mass;
• "Grade" refers to the degree of filtration. For each climatic zone, the temperature range will be different.

For arctic climates - from -22 ° С to -44 ° С, for moderate - from -5 ° С to -20 ° С.

They also highlight additional technical requirements for the Euro standard. These are indicators of fractional composition, kinematic viscosity and lubricating efficiency.

Diesel Fuel Improvement (Additives)

If, due to certain circumstances, it is necessary to change the chemical properties of the fuel, the use of special additives would be the best solution. Unlike the same separators and filters, they do not purify the fuel, but change its composition by adding certain substances. Having a poor understanding of their features, many consumers buy a low-quality product that can even lead to engine breakdown. In addition, it must be borne in mind that even the highest quality additives can have a negative effect if they are used incorrectly. This is especially important for foreign vehicles, which are particularly sensitive to fuel containing these components.

The problem is relevant for the domestic market due to the very mechanism of supplementation with additives. The same diesel fuel is produced at the country's oil refineries, after which it goes to gas stations. Modern technology allows filling station owners to monitor the condition of their product and, if necessary, "improve" it. But since this is not controlled by the state in any way, the amount of low-grade fuel has increased dramatically in recent years.

Bacteria begin to multiply in fuel that is in the tank for a long time. To combat them, special additives are used that kill them and do not contribute to further growth.

For diesel fuels with a low sulfur concentration, antiwear additives are used. Since this type of fuel is characterized by low lubricating properties, its use can seriously damage all moving parts of the engine. They compensate for the low sulfur content.

Fuel additives are used to improve engine starting and overall efficiency. They are responsible for increasing the cetane number. It is rational to resort to them in cases where the product has a high lubricity.

If diesel fuel is used in regions where constant subzero temperatures (up to -40 degrees Celsius) are possible, then in such cases it is rational to add special depressors. They lower the temperature at which the fuel freezes.

A mixture of diesel and kerosene

There are several types of diesel fuel. So, in the summer, the mechanisms operate on L-grade fuel - it is used when the ambient temperature is zero or above zero degrees. For colder conditions, the winter grade - Z is used, which allows operation in cold conditions when the environment drops to -20 degrees. There is also a special diesel fuel, called arctic, which allows the mechanism to operate in super-cold conditions down to -50 degrees.
In situations where the required brand of diesel fuel is not at hand, you can use different substitutes. This includes replacing it with lighting kerosene or using it in mixtures with diesel fuel of other brands. How much kerosene exactly needs to be added to diesel fuel depends on the temperature regime at which solidification occurs. The calculation is made from a 25 percent addition of kerosene by 8-12 degrees lowering.

At the same time, you need to know that it is not recommended to constantly use substitutes, since the increase in the rigidity of the engine, which certainly occurs during replacement, leads to an increase in the wear of the engine itself.