Study On Combustion Characteristics Of Single Mg And Al-Mg-Zr Alloy Particles

Magnesium metal(Mg)has the advantages of low ignition point,low boiling point,good flammability,gas-phase diffusion flame formation,and high burning rate.It is widely used in aerospace fields such as powder ramjet and solid rocket propulsion.Compared with aluminum(Al),the amount of heat released when a unit mass of Mg is combusted with oxygen is lower.Therefore,a small amount of Mg powder is usually added while adding Al powder to the solid propellant or prepared into a Mg alloy form,to improve its ignition performance since Mg is easy to combust.In this paper,Mg and Al-Mg-Zr ternary alloys were selected as the research object.Aiming at the problems of unclear understanding of the combustion process of Mg and Mg alloys and in-depth combustion mechanism,a single laser ignition and microscopic high-speed imaging experimental system was built,to reveal the physical and chemical processes involved in the combustion process with high temporal and spatial resolution,to obtain the ignition and combustion characteristic parameters,and to combine the various characterization data of the original sample and combustion products to analyze the combustion of Mg and Al-Mg-Zr alloys mechanism.A laser-induced ignition experiment was carried out on a single micron metal Mg sample in the air.At the same time,SEM,EDS,XRD,XPS and other test methods were used to analyze the morphological characteristics,element composition and content,and crystal structure of the particles.The analysis results show that a single metal Mg in the air mainly undergoes four stages:offset expansion,melting,gasification,and full combustion.The gasification stage takes the longest time,and the combustion is gas phase combustion.Ignition delay time and combustion time are closely related to particle size and ignition power density.Comparative experiments under pure oxygen,nitrogen and argon atmospheres found that:Mg has a lower ignition probability under pure oxygen conditions.It does not burn under pure nitrogen and argon conditions,but it explodes strongly under pure nitrogen conditions,mainly due to the escape of nitrogen dissolved in liquid Mg.Under argon conditions,Mg only vaporized.Based on the results of experimental analysis,a physical model of the combustion mechanism of metallic Mg and the corresponding particle phase and gas phase equations was established.The same experimental study was performed on a single micron Al-Mg-Zr alloy sample in air.The results show that:in the air atmosphere,the combustion process of Al-Mg-Zr alloy is mainly divided into explosion,Mg combustion and Al combustion.The thermal decomposition of MgO2 in the alloy leads to a micro-explosion,which promotes the diffusion of oxygen in the Al combustion process and makes Al combustion more fully.The ignition delay time of Al-Mg-Zr alloy is relatively short,and its ignition and combustion characteristics depend on particle size and ignition power density.At the same time,a laser ignition experiment was carried out on the combustion of Al-Mg-Zr powder in pure O2,pure N2 and air,and the combustion products were analyzed.The results showed that:A violent micro-explosion occurred during the combustion of Al-Mg-Zr alloy powder in pure O2.There was no flame in N2,and there was obvious smoke plume,which appeared as a "mushroom cloud",but no obvious smoke and flame were observed in the air;the combustion products in pure O2 were mainly MgO and Al,and the combustion of Al is incomplete.Due to the low content and the high melting point of Zr,Zr does not undergo oxidation reaction.Its main function is to adjust the crystal form of the alloy material Al3Zr to avoid the agglomeration of elemental Al.This paper experimentally studies the laser ignition and combustion characteristics of metallic Mg and Al-Mg-Zr alloys,which is of great significance for the development of metallic Mg and alloys in propellants.