Particle radiative feedback in ammonium perchlorate deflagration

Abstract

The deflagration behavior of ammonium perchlorate (AP) with carbon black and copper chromite catalyst additives was studied over a pressure range of 4.3-171 MPa (50-2500 psig) using light transmission and emission measurements in a window bomb and burn rate measurements in a conventional strand burner. It was found that a maximum value of the lower pressure limit P DL exists at intermediate values of carbon black concentration similar to that already reported for copper chromite catalyst. It was also found that sufficiently high concentrations of carbon black augment the steady deflagration rate of AP. Since carbon black is not a catalyst of AP decomposition, it is postulated that particle radiative feedback is more likely to be the cause of the observed behavior than previously suggested catalyst effects. To quantify the amount of radiative heat feedback, flame temperature and emissivity values were calculated from light emission/transmission measurements. These calculations yielded flame temperatures between 1406 and 1449 K and a value for the effective particle absorption efficiency over diameter Q a /d of 4.1 jun" 1 in good agreement with expected values. A simple analysis shows that the observed trends (increasing P DL at low particle concentrations and decreasing P DL at higher concentrations) can be predicted from simple radiative transfer considerations together with particle and matrix continuity equations. c s d D fm f. H I /o k M s n N P q Qa r R Sl-4 SI T T s TCP Nomenclature= absorption coefficient, jnm~l = absorption cross-section, cm 2 = AP specific heat, 0.33 cal/g • K = particle diameter = diameter of pellet and flame, 1.27 cm = mass fraction of particles = volume fraction of particles = thickness of isothermal radiative surface zone, /Lim = intensity, W/cm 2 • nm • sr = incident intensity = proportionality constant, including efficiency of optics and detector sensitivity, V/(W/cm 2 • nm • sr) or imaginary component of refractive index, n -ik = height of flame zone, cm = mean molecular weight of combustion product gases, 28.4 g/mole = real part of refractive index, n -ik = number density of particles, cm ~3 = pressure, psi or Pa = net radiative heat loss from surface, cal/cm 2 • s = particle absorption efficiency = linear burn rate, cm/s, or particle radius, jmi = universal gas constant, 1206.2 psia • cm 3 /mole • K = signal voltages = spectral irradiance = 7A12, W/cm 2 • nm = temperature, K = overall transmittance for two combustion bomb windows = flame temperature, K = surface temperature, K = tricalcium phosphate