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In line with the EU preferences, for well-known reasons, the aim is to increase the content of rapeseed methyl ester (RME) in standard diesel fuel. Currently (2021), the obligatory RME supplement to the diesel fuel is 7%, but in the near future it will be 10%. Unfortunately, the increase in the amount of methyl esters of vegetable oils is associated, among other things, with a reduction in the stability of such a fuel during storage, an increase in the deposits of the combustion chamber and fuel injector, and an increase in the concentration of NOx in the exhaust gases of the engine. The increase in NOx emission in the exhaust gas results then mainly from the influence of RME on the extension of the auto-ignition delay, and therefore from the increase in this case of the maximum rate of kinetic combustion and consequently the increase of the maximum combustion temperature. Therefore, in order to avoid the negative effects of increasing the amount of RME in the fuel, the nitrON package was used, containing 3 different additives: stabilizing, cleaning and increasing the cetane number of the fuel. The tests were carried out with the use of the Caterpillar C27 engine of the 6Dg locomotive, which is a modernized SM42 locomotive with an engine produced by Cegielski-Poznań. After the modernization, the modernized unit also uses a V-shaped engine, but already a 12-cylinder (not 8-cylinder), with a displacement of only 27.0 dm3 (not 81.6 dm3) and a power of 560 kW (instead of 530 kW) with the common rail system (in the previous version, sectional injection pumps were used). The 6Dg locomotive was connected to a water resistor and it was used to measure the hourly fuel consumption of the engine (fueled with B7 fuel and B7 + the nitrON fuel), NOx concentration and exhaust smoke for 3 points of test F, in accordance with UIC 624 (Directive 2004/26/WE). The concentration of the nitrON additive in the test fuel was 1500 ppm (v / v). The nitrON package consists of 2-EHN which increases the Cetane Number, an oxidation stability component, a corrosion inhibitor and a lubricity additive. The tests showed that the effectiveness of the nitrON package with regard to the reduction of hourly fuel consumption (Gp) and the reduction of NOx concentration in the exhaust gas depends on the engine operating point. The greater the load and/or the engine speed, the more intense the action of the nitrON package, which is undoubtedly related to the favorable influence of high temperature on the effect of these additives to the fuel. For example: for idling, the reduction in Gp is only 1.5% (in relation to Gp for an engine fueled with fuel without nitrON), but for a very high engine load and nominal rotational speed, the percentage reduction in Gp is as high as 5%. Similarly, for the concentration of nitrogen oxides in the exhaust gases - the reduction of NOx concentration for idling (due to the use of nitrON) is approx. 10%, while for a high engine load, the percentage reduction of NOx concentration in the exhaust gas (thanks to the use of nitrON) exceeded 15%.