# Oxygenated Diesel Fuels and Their Effect on PM Emissions
## 4 Tests Results and Discussion
It was shown in [67] that in addition to a significant reduction in PM emissions, the addition of glycol ethers to diesel fuel is beneficial for diesel particulate filter (DPF) regeneration processes (soot activation energy is reduced), as well as for extending DPF life (lower soot ash content) without affecting the efficiency of exhaust gas filtration. The test results presented by other researchers confirm the usefulness of maleates as components of diesel fuel reducing PM emissions. We can mention [PERSON] and [PERSON] [28], who achieved a reduction of PM emissions by using diethyl maleate and dibutyl maleate. They also tested some glycol ethers, but found that they caused less favorable changes in PM emissions than maleates. [PERSON] et al. [68] analyzed 71 potential oxygenated compounds and, based on their physicochemical properties, selected the 8 most suitable oxygenates for use in diesel fuel, including dibutyl maleate. They then performed preliminary emission tests with the use of selected components at a concentration providing 7% of oxygen in fuel [69], in which the fuel containing dibutyl maleate caused a significant decrease in PM emissions and was selected for further, wider research. These more extensive studies [70] performed in several modes of engine operation confirmed the high efficiency of the above-mentioned oxygenate in reducing particulate emissions. In the literature, one can find the results of research on carbonates as components of diesel fuel presented by other researchers. In this context, it should be initially noted that [PERSON] et al. [62] used five oxygenates from the chemical family of carbonates in their extensive research on the influence of oxygenated compounds on PM emissions. Their research was conducted in a similar way to the authors of this article, i.e., in the NEDC cycle with the use of a diesel passenger car. Similar again to our case, it was found that for the same content of different oxygenates in fuel, the greatest reduction in PM emissions was achieved for carbonates. Then, among all the tested carbonates, the most effective ones proved to be diethyl carbonate and diethoxy-2-ethyl carbonate, which, added to the fuel in the amount of 5%, resulted in a reduction of PM emissions by 17-18%. [PERSON] et al. [27] conducted extensive research on the effects of dimethyl carbonate on the combustion characteristics and emissions of a diesel engine. They found that for the 10% content of this compound in the fuel, the smoke emission was reduced by a value between 35% and 50%. It was also observed that the degree of smoke emission reduction is proportional to the content of oxygenates. [PERSON] and [PERSON] [24] presented the reduction of smoke emissions obtained with the use of a component from the carbonate group. [PERSON] et al. [71] showed a significant reduction in soot emissions in the exhaust gas for diesel fuel containing dimethyl carbonate. The authors of [72] showed a strong relationship between the oxygen content in the fuel and the diesel engine exhaust opacity. With small additions of oxygen, the effectiveness in reducing smoke emissions increases rapidly. Above 10% \(m/m\) of oxygen in the fuel, further increase brings only a slight reduction in smoke emissions. A greater efficiency in reducing PM emissions using diethyl carbonate than diethylene glycol dimethyl ether with both components concentrations at the level ensuring the same oxygen content in fuel was observed. In turn, in this study, dimethyl carbonate showed similar effectiveness to diglyme. In the authors' research presented in this article, a small reduction in PM emissions by adding n-butanol (5%) to diesel fuel was observed. This can be partly explained by the significantly lower oxygen content in butanol (21.6% \(m/m\)) compared to the other oxygenated compounds used, where it reached over 50%. Small additions of oxygenates were used in order not to significantly change the physical properties of the obtained fuel blends.