Combustion and soot emission characteristics of hydrous ethanol gasoline direct injection engine

In recent years, the gradual increase in automobile production has accelerated the consumption of petroleum resources, and a large amount of harmful exhaust gas has also brought great threats to the climate and human health. It is the general trend to seek low-carbon, clean and renewable alternative fuels and realize energy diversification. Gasoline direct injection (GDI) engines have been widely used due to the advantages of high efficiency and cleanliness, but the problem of higher particulate emissions has not yet been resolved. As an alternative fuel for engines, ethanol has the advantages of high- octane number, low pollution, strong renewability, safety and non-toxicity, and good compatibility with gasoline. Compared with absolute ethanol, hydrous ethanol is less sensitive to moisture in the air, and it is more stable when mixed with gasoline. Exhaust gas recirculation (EGR) technology can effectively reduce pumping losses, reduce fuel consumption, and reduce NOx emissions. The introduction of EGR in gasoline direct injection engines can lower the combustion temperature, and the dilution effect of exhaust gas can reduce the local concentration of the mixture, which is beneficial to inhibit the soot generated by the fuel cracking and dehydrogenation reactions. In this study, the three-dimensional simulation was carried out by using CONVERGE software coupled with the combustion mechanism of hydrous ethanol gasoline and the soot model, to explore the effects of the combination of hydrous ethanol and EGR on the combustion and soot generation characteristics of GDI engine. The results showed that the increase of the volume fraction of the hydrous ethanol accelerated the flame propagation speed, shortened the combustion duration. The soot precursors (PAHs) control the nucleation and growth of soot. The formation of soot can be inhibited by the oxygen-content characteristics of hydrous ethanol gasoline and the high activity OH. Compared with E0 (hydrous ethanol volume fraction is 0%), the peak mass of soot precursors of E20W (hydrous ethanol volume fraction is 20%) A1 (benzene), A2 (naphthalene), A3 (phenanthrene) and A4 (pyrene) were reduced by 60.0%, 54.5%, 73.3%, and 52.4%, respectively, the peak of soot mass was reduced by 63.6%, and the peak of soot quantity density was decreased by 40.0%. The introduction of EGR reduced the combustion efficiency, increased the mass of PAHs and soot generation, and reduced the soot quantity density. The addition of hydrous ethanol could improve the combustion efficiency in the EGR environment and reduce the amount of unburned HC and soot generation. Compared with pure gasoline, hydrous ethanol gasoline combined with EGR technology reduced the negative impact of EGR on combustion and soot emissions. It can be concluded that the combination of EGR and hydrous ethanol gasoline could improve combustion characteristics but decrease soot production, further enhance the performance while reduce particulate matter emissions of GDI engine.