Ignition of single nickel-coated aluminum particles

Ignition mechanism of nickel-coated aluminum particles

“…Unfortunately, attempts to quantitatively analyze the temperature vs time curves, which would allow extrapolation to smaller particle sizes, were unsuccessful due to an uncertainty of the particle absorptivity. Note, however, that prior experiments with single 100-µm Ni-coated Al particles (51 wt% Ni) injected into a hot furnace reported that the critical ignition temperature (minimum gas temperature required for ignition) is ∼830 • C in Ar atmosphere [14]. Taking into consideration an expected difference between the particle and gas temperatures at the ignition limit, as well as thermocouple errors, we can state that this result coincides with measurements made in the current study.…”

“…The large heat losses may also explain the nonignitability of 6 wt% Ni particles, which contradicts prior observations for small (32-40 µm) levitated Ni-coated Al particles, where the ignition delay times in air were equal for the Ni content range from 5 to 15 wt% [14]. The nonignition of 2.5-mm 6 wt% Ni particles is likely associated with large heat transfer to the thermocouple wires and lower heating rates, coupled with premature Ni consumption.…”

“…In a prior study [14], the critical ignition temperature of Ni-coated Al particles in O 2 /Ar (20-50% O 2 ) mixtures was higher by ∼100 • C as compared with measurements in pure Ar atmosphere. This implies that O 2 does not improve the ignition of Ni-coated Al particles, but further experimental verification is needed.…”

“…To provide insight into the ignition and combustion of single Ni-coated Al particles, experiments were conducted involving laser ignition of electrodynamically levitated particles (diameter 30-100 µm) in different gas environments (air, O 2 , CO 2 , Ar) [13,14]. In addition, single Ni-coated Al particles (100-125 µm) were injected into a vertical, preheated tube furnace to determine critical ignition temperatures [14].…”

“…In addition, single Ni-coated Al particles (100-125 µm) were injected into a vertical, preheated tube furnace to determine critical ignition temperatures [14]. The results indicated that the Ni coating dramatically decreases both the ignition delay time and the critical ignition temperature (by ∼1000 • C) of Al particles.…”