# Oxygenated Diesel Fuels and Their Effect on PM Emissions
## 5 Conclusions  
The harmful effects on human health of diesel particulate matter are indisputable at present. The tests showed that oxygenated compounds in diesel fuel significantly reduce PM even at a low concentration of 5% \(v/v\). The most effective oxygenates, i.e., diethyl carbonate and diethyl maleate, reduced PM emissions in the NEDC cycle by 32% and 25%, respectively. This is a very good result, especially taking into account the simplicity of the solution, which is a 5% addition of a given substance to the fuel. At a concentration of 5%, oxygenates from the group of glycol ethers provided a lower reduction in PM emissions (by about 15%). Thus, in the case of glycol ethers, it is recommended to double their content in fuel, i.e., from 5% to 10%, as according to the obtained results, it also doubles the effectiveness of PM emissions reduction.  
The analysis of the mechanism of the influence of fuel oxygenates on particulate matter (soot) emissions showed that the main determinant of the effectiveness of PM reduction is the oxygen content in fuel, but other factors also play a role. According to the results described in this article (Figure 5), 1% of oxygen in the fuel resulted in an average reduction of PM emissions by 7% to 10%. During the tests, the content of oxygenated compounds did not exceed 10%, so that the physical properties of the fuel did not change significantly compared to neat diesel fuel. Hence, it can be assumed that the observed effect of reducing PM emissions was mainly due to the presence of oxygen.  
The effective action of oxygenated compounds on PM emissions, even at low concentrations, allows their use in serial combustion engines without the need for structural changes. It can also be used as a method of PM emissions reduction from older vehicles/engines that are still in operation but where retrofitting them is not profitable. For vehicles with DPFs, the effect of oxygenated fuels \"at the end of the exhaust pipe\" will be less [86]. However, even in this case, the benefit will be the lower frequency of DPF regeneration, which is not neutral to the environment.  
Some opinions indicate [87; 88] that alternatives to the currently widely used bio-diesel (fatty acid methyl esters--FAME) should be sought. Due to their properties, oxygenated compounds can be components of tailor-made fuels for modern, low-emission engines. Moreover, they can be produced as renewable fuels, in environmentally friendly technologies, such as biomass fermentation (butanol) or in currently developed Power-to-Liquid technologies. In the view of already limited possibilities of modifying conventional parameters of diesel fuels (density, PAHs content, sulfur content, etc.) the use of oxygenated compounds is a promising way to trade on the potential of fuels in PM emissions reduction.  
Conceptualization, M.K. and J.M.; methodology, M.K. and J.M.; validation, M.K. and J.M.; formal analysis, M.K.; investigation, M.K.; resources, J.M.; data curation, M.K.; writing--original draft preparation, M.K.; writing--review and editing, M.K and J.M. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The authors declare no conflict of interest.  
Figure 14: Percentage changes in HC emissions over the NEDC from a test car with fuels containing individual oxygenates at a concentration of 5% \(v/v\) compared to running on conventional diesel fuel.