Investagation Of Interaction Between Turbulence And H₂/CO Premixed Flame Front By Direct Numerical Simulation

China is a country with more coal and less oil and less natural gas,so China's energy consumption structure with coal as its main body has made outstanding contributions to economic and social development while bringing serious damage to the environment of China.Although the government has begun to attach importance to the regulation and optimization of energy structure,this is a long-term process,and coal as a cheap and economy energy will not quickly withdraw from the stage of history,therefore,the efficient and cleaning use of coal has become a top priority.Coal-based multi-generation technology use pyrolysis or gasification method to convert coal into synthetic gas for clean use and by-products can be sold to reduce costs,and it is a clean and efficient coal burning way.The produced syngas generally contains a certain amount of hydrogen,so how to use synthetic gas safely will also become a scientific issue due to the active chemical properties of hydrogen.Numerical simulations have been widely accepted as a means of understanding the mechanism of turbulent combustion,whereas direct numerical simulation can obtain as much flow information as possible without any assumptions on turbulence and the detailed mechanism of reaction can provide insight into combustion.In this paper,a direct numerical simulation turbulence combustion program has been developed based on the low Mach version of Navier-Stokes equation and the detailed mechanism of solving the combustion reaction.The accuracy of the program in turbulent combustion calculation is proved by comparison with the turbulence flame surface interaction experiment result and the laminar flame velocity.The flame surface characteristics of turbulent premixed combustion of hydrogen-containing syngas in many cases are studied in this paper using this program.Firstly,the interaction between the two-dimensional flame surface and the isotropic turbulence in turbulent combustion with different equivalence ratios and different turbulence numbers is studied.It is found that there is a flashback phenomenon in the lean condition after a characteristic turbulence time scale ?.The turbulence produces a pronounced compressive strain on the flame surface and the propagation velocity of the flame surface is greater than its laminar flame speed.However,the probability density distribution of the change in area of a propagating curved surface is symmetrical with zero value,which means the average position of flame surface in the field does not change.The flame length is not related to the equivalent ratio but is positively related to the turbulence number.OH is mostly enriched in the convex surface while less in concave surface.Secondly,the flame surface flame extinction is studied by a two-dimensional vortex pair at different ratios of syngas and different ratios of dilution gas.It is found that the interaction between the turbulence vortex and the flame surface becomes stronger as the ratio of H₂ in the syngas decreases or the ratio of the diluent gas increases,indicating that the detachment time becomes longer and the morphology of the vortex pair changes obviously.However,the change in the interaction is more sensitive to H₂ reduction.While the local extinction phenomenon caused by the vortex pair is essentially due to the rapid reducing of H₂ chemical rate,the combustion of CO will not stop,but the combustion of CO will be slower because of the decreasing local temperature caused by H₂ extinction.After the vortex pair is detached from the flame surface for some time,the flame surface of high H₂ ratio or low dillution gas ratio will become unstable cell flame due to the diffusion-thermal effect.The three-dimensional constant-volume closure method is also used to study the auto-ignition characteristics of the hydrogen-containing syngas under different equivalence ratios,pressures,plasma concentrations and dilution gas ratios in the turbulent environment.It is found that the auto-ignition delay has little to do with the equivalence ratio,but is significantly reduced by increasing the pressure and adding plasma.The pressure is affected by increasing the rate of chemical reaction,and the plasma produced O radicals by decomposition to make the reaction happen easily.Adding the dilution gas can appropriately increase ignition delay.After a series of studies on the specific flame surface,a three-dimensional simulation of near-field free-combustion premixed lean hydrogen-containing syngas jets with addition of O₃ has been carried out.It is found that O₃ starts to affect the composition field and temperature field of the whole field in the axial 8D?9D position.The consumption of fuel obviously accelerates and the temperature increases,but the formation of CO₂ is promoted while H₂O is not.From the observation of the flame surface curve along the time,it is found that O₃ can increase the flame surface area in the period of ignition,and will promote the combustion process of syngas combustion,so that the combustion can occur earlier.From the probability density distribution of the statistics,it can be seen that the flame surface added with O₃ is more likely to be stretched by the turbulent,while the overall distribution of the curvature does not change and the propagation speed of the flame surface is improved.