In this paper, the characteristics of a straight-run diesel fuel sample, narrow diesel fractions, and their blends with a depressant additive are tested and analyzed. The efficiency of the depressant additive action on the low-temperature properties of narrow diesel fractions is evaluated. It is shown that the depressant additive is most effective on the pour point of the heavy diesel fraction (300–360 °C) and cold filter plugging point of the light diesel fraction (180–240 °C). The regularities of the effect of narrow diesel fractions on the effectiveness of the depressant additive are established. It is shown that the addition of narrow diesel fractions has practically no effect on the cloud point of the straight-run diesel fuel sample/depressant additive blend. The addition of narrow diesel fractions has a negative effect on the cold filter plugging point of the straight-run diesel fuel sample/depressant additive blend. The addition of the light diesel fraction and middle diesel fraction (240–300 °C) has no significant effect on the pour point of the straight-run diesel fuel sample/depressant additive blend, but the addition of 5 vol % heavy diesel fraction allows lowering the pour point of the blend by 6 °C. The established regularities are explained from the viewpoint of the depressant additive action mechanism. It was found that for a more effective depressant additive action, it is necessary to take into account the content of various narrow fractions in the composition of diesel fuel. It is established that the simultaneous lightening of the fractional composition of diesel fuel (addition of light fractions and/or removal of heavy fractions) and the addition of a depressant additive to obtain low-freezing diesel fuels is impractical. However, the addition of small amounts of heavy diesel fractions simultaneously with depressant additives increases the possibilities for the production of low-freezing grades of diesel fuel as well as expands the feedstock pool of enterprises for the production of fuel. In the future, the identified regularities of the influence of the narrow diesel fractions will allow us to detail the general mechanism of diesel fuel and depressant additive interaction.

In this paper, the viability of expanding the feedstock base of diesel fuel production by the involvement of the heavy diesel fraction and the use of cold flow improvers was shown. The influence of the heavy diesel fraction content in the diesel fuel composition on its low-temperature properties and the effectiveness of the cold flow improver were studied. It was established that the involvement of a small amount of the heavy diesel fraction (up to 3 vol%) increases the effectiveness of the cold flow improver in relation to the cold filter plugging point. The following recipes of diesel fuel production were recommended: the involvement of up to 5 vol% heavy diesel fraction allows producing fuel of the summer grade; the involvement of up to 5 vol% heavy diesel fraction and the cold flow improver allows producing fuel of the inter-season grade; and the involvement of up to 3 vol% heavy diesel fraction and the cold flow improver to produce fuel of the winter grade.