Investigation On The Initiation And Self-sustaining Propagation Of The Magnesium Particle-air Mixture

Because of its advantages of energy density,ignition characteristics and combustion efficiency,magnesium particles have broad application prospects as a fuel or additive in detonation power systems.In this paper,based on the existing models of powder fuel detonation and experimental techniques,the characteristics of the detonation wave of magnesium particle-air mixture was studied.The feasibility test of magnesium particle-air mixture detonation was carried out and the main factors affecting the velocity,stability and propagation mode of the detonation wave were analyzed,which provided theoretical and technical references for the application of magnesium powder fuel in the detonation power system in futureThe background and significance of this paper were introduced,and the research progress of the powder fuel detonation in aspect of experiments and numerical simulations are were summarized.The main factors affecting the velocity,stability,propagation mode,flow field structure and cell evolution of the detonation wave were summarized.The case of powder fuel applied to detonation engine or chamber were analyzed.The research progress of ignition and combustion models of magnesium particles were introduced.The experimental test device,the combustion diagnostic test method and the numerical simulation method used in the powder detonation were discussed and analyzed.The existing problems about powder fuels applied to the detonation engine were proposed and the main contents of this paper was introduced.A two-phase CJ model for describing the detonation of magnesium particle-air mixtures was established.The loss of expansion work of the gaseous working medium and the effect of the reactant/product phase-transition process on the final temperature of the mixture were considered.The theoretical impulse performance of the air-breathing continuous rotary detonation engine using magnesium powder fuel was predicted based on the two-phase CJ model.A two-phase ZND model was further established to study the stable self-sustaining propagation conditions of the detonation wave of the magnesium.The variations of the stable velocity,the size and the CJ plane parameters inside the detonation wave with the phase-transition and the initial concentration and diameter of the magnesium particle were obtained.A one-dimensional unsteady model for the detonation of magnesium particle-air mixture was established to numerically simulate the detonation wave propagation process and its internal flow field distribution.Considering the loss of the wall,the propagation velocity and the thickness of the detonation wave decreased with the decrease of the inner diameter of the detonation tube.The variation of the velocity and thickness with the initial concentration and equivalent ratio of magnesium particles with considering the wall loss is quite different from that without considering the wall loss.The detonation wave velocity and thickness with a double-size-distribution initial particle size is more than that with an equivalent single-size-distribution.When the magnesium oxide fusion occurs near the CJ plane,it has no significant effect on the stability of the detonation wave propagation but the thickness becomes more obviously.Considering the deposition of combustion products on the particle surface,the detonation wave velocity increase while the corresponding thickness of the detonation wave remains almost unchanged with the increase of the deposition rate.Reasonable the ignition conditions can significantly reduce the propagation distance before the detonation wave to the steady state.A two-dimensional unsteady detonation wave model of magnesium particle-air mixture was established.When continuous rotating detonation wave achieves stable self-sustaining propagation,periodic perturbation vortices appeared at the interface between new mixture and products.The insufficient height of the ignition zone would lead to the failure of the detonation intiation.The self-sustaining propagation velocity of the detonation wave decreased with the decreased of the calculated domain length,while the length was reduced to a critical value,the continuous rotational detonation mode could not be maintained.The total injection pressure had no obvious influence on the self-sustaining propagation of the detonation wave with an enough domain length.The velocity of detonation wave increased first and the decreased with the increase of equivalent ratio,and the lower limit of equivalent ratio was lower than that of the one-dimensional model.The velocity of the detonation wave decreased with the increase of the particle size.Experimental investigation for the detonation of the magnesium particle-air mixture was carried out.Scanning electron microscope,energy spectrum analyzer,Malvern laser particle size analyzer and X-ray energy spectrometer were used to characterize the morphology,element distribution,particle size distribution and element valence of the reactants and products.The most suitable test parameters,such as the gas source pressure,valve opening time,ignition preparation time and ignition energy,were obtained with the self-designed test system.Magnesium particles with an average diameter of 6 microns performed best.The experimental velocity of detonation wave agrees well with the numerical simulation results.