Experimental study on the explosibility of aluminum dust/methane/air hybrid mixtures

Aluminum particles are currently widely used in propulsion system, as the oxidation of aluminum metal is characterized by a significant release of heat. Indeed, the combustion of aluminum particles has been the subject of numerous studies due to its widespread use, notably in solid rockets to increase the thrust of aerobic rocket engines and reduce the oscillatory instabilities in the combustion of hydrocarbon fuels. Securing industrial production sites and storage facilities for these rocket engines requires an understanding of the ignition and propagation mechanisms of these hybrid mixtures.,Consequently, this article proposes a study of the ignition and combustion processes of aluminum particles in the presence of methane over a wide range of compositions to establish its explosive range. Because of the very high sensitivity to ignition of these aluminum-methane-air hybrid mixtures, the determination of the lower explosive limit (LEL) is a central point of this study.,In a first part, severity parameters representing the overpressure and the rate of pressure rise of hybrid methane/aluminum dust explosions are experimentally investigated in this paper. Experiments were carried out in the modified 20L sphere, in order to introduce the gas. Aluminum dust with a median diameter of 21.36 µm was mixed with methane at a concentration of 0% to 15%. The results of the hybrid mixtures were compared to the severity parameters of pure aluminum dust and pure methane gas, in order to understand the effect of adding methane fractions to aluminum dust and conversely. The explosion tests show that the addition of flammable gas to dust increases the maximum explosion pressure and the maximum rate of pressure rise. However, the increase in the maximum rate of pressure rise was more pronounced than the explosion pressure one. The findings also showed that the explosive limits of methane were affected by the addition of aluminum dust.,In a second part, flame temperatures and ignition delays of hybrid mixture methane/aluminum dust were determined. It has been shown that the addition of aluminum dust particles is a promising way of improving methane combustion performance by decreasing ignition delay.