## 1 Introduction
The use of such a system allows achievement of the goals set through the use of alternative fuels and pollution reduction, at the same time analyzing them more intensively for the specifics of the engine's operating process [26; 27; 28; 29]. Various injection strategies have been used to analyze the use of natural gas/diesel blends in compression ignition engines [30]. Diesel engines can be modified so that natural gas inside the intake manifold is fumigated [31]. The time of injection of diesel and the proportion of natural gas have a major impact on the combustion mechanism, and this impact becomes even more evident at partial loads [32]. The mixed natural gas combustion stage can be improved by using a slower natural gas injection time [33]. The use of a dual injection strategy at the maximum pressure allows achieving thermal efficiency of more than 45% and limiting NO\({}_{\text{x}}\) emissions. When using a single injection strategy, thermal efficiency is more than 45% with the engine operating in the range of low and medium loads, and a mere 35.5% at high loads, which can be explained by higher combustion losses [34]. With the engine operating at low loads and using various injection strategies, the combustion of dual fuel (natural gas and diesel blend) can be improved by a lower diesel start of injection (SOI) and a greater opening of the EGR (Exhaust gas recirculation) valve [35]. Increasing injection pressure significantly reduces the amount of unburnt methane in dual fuel engines with split injection. However, with methane concentration having reached 65%, the injection pressure has an impact on emissions of unburnt methane [36]. The amount of unburnt methane may form due to the temperature being too low at the cylinder wall, but increasing the injection pressure will increase the speed of methane flame propagation. Peroxide compounds have been found to have a significant influence on the combustion temperature during combustion of natural gas and diesel blends [37]. Correspondingly, slightly opening the EGR reduces the amount of unburnt methane, however, an increase of the degree of the opening of EGR proportionately increases methane content [38]. With increasing the amount of natural gas in the blend, the curves of the speed of heat emission have one peak only initially, then turn into two peaks, and finally changing to a nearly single peak [39]. [PERSON] et al. [40] claimed that with the natural gas concentration having reached 55% and above, the combustion process deteriorates, even though the calculations show that the combustion process is normal supplying gas at 0 to 60%. The respective use of the NSGA-II (Nondominated sorting genetic algorithm) optimization algorithm allows optimizing such parameters as the gas spray angle and the time frame between the spray of diesel and gas [41]. The supply of natural gas and diesel blends to a rotary engine revealed that the combustion process occurs at the front and the middle of the combustion chamber. The total speed of fuel combustion improved having increased the amount of natural gas supplied, which in turn led to an increased rate of flame propagation. Compared to diesel, supplying up to an additional 20% of natural gas increased the maximum combustion pressure by ~24% [42]. In the event of an auxiliary ignition, natural gas accumulates at the end of the combustion chamber and diesel at its front and middle, and when delaying the injection time, the blend itself becomes more concentrated due to a shorter mixing period [42]. When changing the injection time, the maximum cylinder pressure correlates with the second peak of the speed of heat release, while having extended the shape of the injection nozzle by 2 cm, the combustion process deteriorates also increasing pollutant emissions [43]. The use of Jatropha biodiesel and biogas blends has shown that the CO\({}_{2}\) content of the biogas does not affect the thermal efficiency of the engine.