Abstract
Metal magnesium (Mg) fuels have been widely used in rocket propellants. The combustion study on individual Mg microparticles is crucial to the in-depth unveiling of the combustion mechanism of Mg-based propellants. In this paper, a new experimental setup was proposed to directly observe the combustion of individual micron-sized Mg particles, based on laser ignition and microscopic high-speed cinematography. The combustion process of individual Mg microparticles could be directly and clearly observed by the apparatus at high temporal and spatial resolutions. Individual Mg microparticles took gas phase combustion, and mainly underwent four stages: expansion, melting, gasification, ignition, and combustion. The ignition delay time and total combustion time had an exponential decay on the particle diameter, and they had a linear decay on the ignition power density. The melting took a dominant role in the whole burnout time. The gas-phase combustion flame seemed thick, inhomogeneous, and ring-like structure. The combustion model of individual Mg microparticles was built through combining the experimental results with the SEM, XRD, XPS, and EDS analysis of original samples and combustion residues. This study will be beneficial to understand the combustion process and reveal the combustion mechanism of metal microparticles besides Mg.
Highlights
Compared to metals like aluminum and boron, magnesium (Mg) has the advantages of lower ignition temperature, shorter burn time, smaller molecular weight of combustion products [1,2,3], and lower oxygen consumption, which can burn completely at low oxygen fuel ratio in ramjet flying at high altitude [4]
The results showed that the combustion of Mg particles in CO2 consisted of two chemical reaction processes, i.e., gaseous combustion and heterogeneous reaction at the particle surface, but the whole combustion process of vapor phase was controlled by the diffusion rate
Video S1 was set an example to analyze the combustion process, which demonstrated the combustion of an individual Mg microparticle induced by a CW laser with an ignition power density of 0.96 × 105 W/cm2
Summary
Compared to metals like aluminum and boron, magnesium (Mg) has the advantages of lower ignition temperature, shorter burn time, smaller molecular weight of combustion products [1,2,3], and lower oxygen consumption, which can burn completely at low oxygen fuel ratio in ramjet flying at high altitude [4]. The combustion of Mg particles in air is used in conventional ramjet engines, and widely used in powdered fuel ramjets. The reaction of metal particles with the air produces high temperature gas, the high temperature gas enters the secondary combustion chamber to drive the ramjet [5]. In a powdered fuel ramjet, the high-energy metal powder can directly enter the precombustion chamber in the form of two-phase flow under the action of fluidized gas and react with the ram air [6]. It is of great significance to study the ignition and combustion of Mg particles in air, to further reveal the combustion mechanism of solid rocket propellant and applied in powdered fuel ramjet
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