Determination of the maximum effective burning velocity of dust–air mixtures in constant volume combustion

Abstract

The reactivity of a combustible dust cloud is traditionally characterized by the so-called K St value, defined as the maximum rate of pressure rise measured in constant volume explosion vessels, multiplied with the cube root of the vessel volume. The present paper explores the use of an alternative parameter, called the maximum effective burning velocity (u eff,max ), which also is derived from pressure-time histories obtained in constant volume explosion experiments. The proposed parameter describes the reactivity of fuel-air mixtures as a function of the dispersion-induced turbulence intensity. Procedures for estimating u eff,max from tests in both spherical and cylindrical explosion vessels are outlined, and examples of calculated values for various fuel-air mixtures in closed vessels of different sizes and shapes are presented. Tested fuels include a mixture of 7.5% methane in air, and suspensions of 500 g/m 3 cornstarch in air and 500 g/m 3 coal dust in air. Three different test vessels have been used: a 20-l spherical vessel and two cylindrical vessels, 7 and 22 l. The results show that the estimated maximum effective burning velocities are less apparatus dependent than the corresponding K St values. r

Review of the DESC project

“…Furthermore, for a given dust sample, the method does not require parameters such as the volatile content, the exact chemical composition, or the particle size distribution. As for the concept of 'maximum effective burning velocity' (Pu, Jarosinski, Johnson, & Kauffman, 1990;Pu, Jia, Wang, & Skjold, 2006), the current approach is less sensitive to the effect of energetic ignition sources and varying turbulent flow conditions in the vessel, compared to the K St value (Fig. 1).…”

Correlations for flame speed and explosion overpressure of dust clouds inside industrial enclosures

“…He used niacin amid, Lycopodium, RDX and silicon dust. Pu, Jia, Wang, and Skjold (2007) performed constant volume combustion tests on both dust-air and gas-air mixtures in vessels of different shapes and volumes. They used the concept of maximum effective burning velocity, that is the burning velocity of an idealized flame with the same pressure-time trace of a real dust flame, and found: a near linear correlation, between the burning velocity and the initial turbulence intensity up to 3 m/s, almost independent on shape and volume of test vessel; linear correlations, vessel dependent, between K St values and the turbulence intensity at the time of ignition.…”

Influences of the Cloud Shape of Fuel-Air Mixtures on the Overpressure Field

“…Up to now, influencing factors of the overpressure of fuel-air cloud have been widely studied. Some works on the enclosed space have paid attention to the influencing factors of the overpressure production process of gas-liquid twophase, gas-solid two-phase, and gas-liquid-solid three-phase within the vessel in laboratory [2][3][4][5][6][7], such as the location of the detonation initiation point [8,9], energy [10] and ignition way [11], particle size [12] of fuel-air mixtures, and fuel type [13]. Moreover, the related computational model had been established [8,14].…”