## 1 Introduction
The authors found that the reduction in CFPP depends not only on the selected additive and its concentration, but also on the composition of the fuel. The authors of work [25], together with depressant and depressant-dispersant additives, introduced light delayed coking gasoil, heavy diesel fractions from vacuum columns of primary oil refining plants, and heavy diesel fractions from an atmospheric column into diesel fuel and vacuum distillates of various fractional compositions. According to the test results, it was noted that this method significantly reduces the PP of the diesel fuel and gives high, positive depression indicators. In [26], the authors studied the composition of diesel fuel before adding various depressant additives to it. It has been established that the same additive works differently in fuels of different compositions. The authors of [27] note the influence of the fractional composition of diesel fuel on the effectiveness depressant additive. And in work [28], the structural-group composition of three winter diesel fuels was studied and its influence on the low-temperature properties of the fuels was considered. The influence of the component composition of diesel fuels on the effectiveness of anti-wear and depressant-dispersant additives is noted and it is shown that a high content of saturated hydrocarbons, primarily medium-molecular n-alkanes and arenes with a higher proportion of substitution, leads to a deterioration in low-temperature properties. The works [29] presents the results of the depressant additives effectiveness on the diesel fuel low-temperature properties study, using the summer fuel sample. The authors found that the depressant additives effectiveness depends on the total content of n-paraffin hydrocarbons in diesel fuel. In the works of authors [30; 31; 32; 33] a hypothesis was put forward about the existence of an optimal concentration of n-paraffin hydrocarbons in diesel fuel, within which the greatest effect of the depressant additive is achieved. As a literature review has shown, there are many studies devoted to the synthesis of new depressant additives or comparison of their effectiveness. In recent years, more and more researchers are paying attention to the composition of diesel fuel as a factor determining the effectiveness of depressor additives. An important practical consequence of these studies is the possibility of increasing the efficiency of depressant additives by modifying the composition of diesel fuel. The addition of substances that enhance the action of depressant additives can make it possible to produce fuels with improved low-temperature properties without significant costs for technological conversions. In addition, these studies make a significant contribution to understanding the mechanism of interaction between substances included in depressant additives and compounds that make up diesel fuels. Therefore, it is extremely important to identify patterns and develop ways to increase the depressants effectiveness by adjusting the composition of diesel fuel, and the purpose of this work is to study the effect of adding n-paraffins on the depressant additives effectiveness.