Theoretical And Numerical Study Of Detonation In Two-Phase Systems

Unsteady detonation in gas-fuel droplet systems and suspended aluminum dust was theoretically, numerically studied in this thesis. A model of detonation in two-phase systems was set up and numerically simulated with finite difference method. Numerical simulation program was designed and used to calculate the development and propagation of detonation in two-phase systems. The parameters of detonation in two-phase systems were obtained. Detonation limit and critical ignition energy were also obtained by calculation.The investigation for detonation in two-phase systems past years was reviewed and summarized. The problems related on the two-phase detonation were discussed. The problem involved in two-phase detonations was reviewed to know what was the most concerned in the research.ZND model of two-phase detonation was reviewed to understand how to consider the chemical reactions and the effect of two-phase flow between gas and particles in the systems. It was realized the deficiency of inchoate ZND model such as the over-simplified of the chemical reactions.A model was set up to describe unsteady detonation in gas-fuel droplet systems. The change of components in gas was taken into account. Chemical reaction was described with one-step and three-step reaction mechanisms. Numerical simulation results were well agreement with experimental ones. The influence of parameter of chemical reaction rate was further calculated. It was indicated that parameter of chemical reaction rate had little influence on the parameters of detonation in gas-fuel droplet systems whereas the detonation limit was obviously influenced from the results of calculation. In the same condition of ignition energy, the greater of chemical reaction rate, the lower of lower detonation limit and higher of upper detonation limit. Critical ignition energy was also calculated. The critical energy as the equivalence ratio (j)=2 was much more than that as =1. This result was consistent with the experimental one in gas detonation.The shock ignition of aluminum particles was analyzed in this thesis. The acceleration, rising of temperature by heat transfer of the particle was calculated in the flow field behind shock waves. The ignition time delay of particle was obtained and compared with experimental one. It was assumed a new criterion for shock ignition of aluminum particles. It was based on the analysis of thermal stress of aluminum particles. The results showed that as the temperature of aluminum particle increased about 70C, crack was developed in the oxide film shell of the particles. The criterion was that if the crack was enlarged by gas flow behindshock wave and the oxide film lost its protection to aluminum as the temperature of particle reached aluminum melting point and the aluminum was all melted, aluminum particle would be ignited, otherwise aluminum particle would be ignited at its oxide melting point.Model of the detonation in suspended aluminum dust in detonation tube was set up and numerically analyzed. The differences of velocity and temperature between gas and particles were considered. The dissipation by the convective heat transfer and viscosity through tube wall was taken into account. It was considered the influence of increase of surface area of aluminum particle because of its coarseness on the detonation velocity and ignition of particle. New criterion of ignition of aluminum particles in detonation waves was used. The decomposition of aluminum oxide was taken into account. Development and propagation of aluminum dust detonation in detonation tube was numerically simulated. Velocity of detonation and ignition distance of particles was obtained and well agreement with experimental ones. The distribution of pressure, density, velocity and temperature in the flow field of detonation wave was also obtained. The parameters of detonation in two-phase systems with different concentration were calculated and the lower detonation limit in suspended aluminum dust was very low.The nonlinear instability of one-dimensional detonatio...