Effect Of Ethylene Doped Hydrogen On The Formation Of Soot And Polycyclic Aromatic Hydrocarbons

Hydrogen has attracted wide attention because of its cleanliness and high efficiency.Adding hydrogen to other fuels to mix combustion not only can reduce emissions,but also improve combustion efficiency.so the study of hydrogen-blended combustion has great significance.Based on numerical simulation,the effects of hydrogen on soot and polycyclic aromatic hydrocarbons(PAHs)formation in ethylene counterflow flame under steady and unsteady conditions were studied in this thesis.Since one-dimensional simplified hypothesis of counterflow flames is validated under the condition of large nozzle burner,the applicability of this simplified hypothesis for small nozzle diameter burner remains to be studied.Firstly,the twodimensional model of counterflow burner is established to comparing the radial distribution of the axial velocity at the nozzle exit,the difference of flame position and product under different conditions.The main conclusions are as follows: the velocity distribution of nozzle exit is not uniform,and the velocity distribution of fuel exit and oxidizer exit is different under the same inlet gas flow rate;The larger the molecular of fuel,the more non-uniform the velocity distribution.moreover,after heating the inlet gas,the velocity distribution of nozzle exit will be more uniform.The velocity of protective gas will also affect the flame position,and the smaller the velocity of protective gas is,the closer the flame is to the fuel exit.When the radial velocity gradient is added,the flame position is closer to the fuel exit than one-dimensional calculation without radial velocity gradient,the flame width is widened,and the soot formation is obviously increased.Secondly,the influence of hydrogen on the formation of soot and its precursors was studied under the condition of correcting velocity and substituting radial velocity gradient.The results show that hydrogen addition increases the flame temperature in general,but the temperature increases very little.Therefore,the thermal effect of hydrogen addition on soot formation can be neglected.The formation of soot and its precursors was also significantly reduced by hydrogen addition.From the view of chemical effect,hydrogen addition inhibits the formation of soot in general.Although hydrogen addition increases the small molecular PAHs,but the increase is not obvious.On the contrary,hydrogen addition decreases the large molecular PAHs obviously,which makes the nucleation of soot decrease obviously after hydrogen addition.And hydrogen addition decreases the reaction rate of HACA significantly.In addition,hydrogen addition reduces the oxidation of soot and promotes the formation of soot,but on the whole,hydrogen addition inhibits the formation of soot.Because the unsteady flame has a wider range of working conditions than the steady flame,the unsteady effects of pollutant chemical hydrodynamics can be predicted more simple.Therefore,the effects of different velocity frequencies and hydrogen addition ratios on the formation of soot precursors in ethylene unsteady counterflow flames are also studied in this paper.The results reveal a net increase in the concentration of aromatic species when the strain rate oscillations are imposed to the flame.When the frequency increases,the amplitudes of the oscillations decrease,and the phase of PAHs among the different frequency increases.The concentration of PAHs in unsteady condition is more than the PAHs in steady conditions,and the concentration of the PAHs in higher frequencies is closer the steady value than the lower frequencies.When the reaction rate of A1 decreases,the amplitude of A1 increases,and the reaction rate of different reaction cause the different phenomenon.When the hydrogen addition increases,The peak of temperature increases,but the peak of PAHs' concentration decreases.Moreover,the amplitudes of A1 and A2 decrease,but the amplitudes of A3 and A4 decrease.