| The accelerated propagation and combustion of premixed flame in a confined environment is a complex and important research topic in the field of fundamental combustion science,which also provides understanding of the burning processes taking place in internal combustion engines.Hydrogen becomes one of the most promising alternative fuels for internal combustion engines by reason of the low pollution of hydrogen combustion.Therefore,the study of premixed flame dynamics and induced accelerated combustion in a confined environment is of great significance for the realization of rapidly controllable combustion,high efficiency application of hydrogen energy and the development of internal combustion engine technology.Firstly,the flame propagation characteristics under the wall constraint were studied,and the squish flame which accelerates along the wall was found and the critical conditions for squish flame have been obtained.The squish flame induced by the wall is a rapidly developing turbulent flame,which greatly increases the flame propagation speed and accelerates the combustion process.For each initial temperature and equivalence ratio,there exists a critical initial pressure,less than which no squish flame is observed.With the increase of equivalence ratio,the critical initial pressure takes on a U-shaped trend.The minimum value of the critical initial pressure is presented near stoichiometric ratio and it increases sharply when the equivalence ratio is close to the lean and rich combustion limits.As the initial temperature increases,the critical initial pressure gradually increases in the case of fuel-lean mixture and gradually decreases in the fuel-rich mixture combustion.Subsequently,based on the analysis of the characteristics of the squish flame,the flow characteristics of the unburn gas in the wedge-shaped space were studied by CFD analysis technology,and the formation mechanism of the squish flame was revealed by theoretical analysis.During the flame propagation process,a large velocity gradient is created by the walls and the flow of the unburn gas in the wedge-shaped space formed by the flame and the two side walls,which induces a strong wall turbulence.When the flame is sufficiently unstable,the strong wall turbulence in the wedge-shaped space causes the near-flame to destabilize or even turn into a turbulent flame,thereby accelerating the rapid propagation of the unstable flame,and finally forming a squish flame.Finally,the propagation and combustion characteristics of the turbulent flame induced by the orifice plate were analyzed,and the the effect of the orifice plate structure on the accelerated flame propagation has been obtained.The principle of the optimal orifice structure has been proposed.As the orifice blocking ratio increases and the bore diameter decreases,the turbulence intensity induced by the orifice plate increases,and the turbulent flame propagation velocity increases.The effect of the bore diameter on the flame propagation speed is small relative to the blocking ratio.There exists an optimal blocking ratio and an optimal bore diameter for each initial condition to minimize the combustion duration.For flames with slow propagation speed and strong stability,the optimal orifice plate structure tends to have a larger blocking ratio and a smaller bore diameter,which can increase turbulence intensity induced by the orifice. |
