Combustion of Boron-Titanium Nanocomposite Powders in Different Environments

Combustion of nanocomposite powders with the bulk composition 2B+Ti was compared with combustion of blended boron and titanium powders with the same bulk composition and with combustion of aluminum in wet and dry gas environments. Nanocomposite powders were prepared by Arrested Reactive Milling. The gas environments were N2/O 2/CH 4 mixtures with oxygen concentration fixed at 22.5 % and methane concentration varied from 0 to 12 %. The experiments were conducted in a constant volume explosion vessel. The mass loads of metallic fuel were determined from thermodynamic calculations to ensure the maximum flame temperature for each metal fuel – gas mixture combination. The calculations showed that despite the higher adiabatic flame temperatures for Al than for 2B+Ti, a greater energy per unit mass of metal fuel was released to produce heated gaseous combustion products in combustion of 2B+Ti as compared to Al. Experiments with Al powders showed that the flame temperature did not change noticeably as a function of gas composition and remained close to 2560 K. The combustion temperature for the nanocomposite 2B+Ti increased from about 2180 to 2370 K as the methane concentration increased from 0 to 12 %. The bulk burn rates inferred from the rates of pressure rise were consistently higher for the nanocomposite 2B+Ti powder, followed by Al and then by the blended 2B+Ti powder. The efficiency of combustion for all the fuels was assessed by comparing the predicted and experimental portions of the combustion energy used to produce the heated gaseous products. Based on this assessment, nanocomposite boron-based fuels outperformed Al for all environments, with the difference increasing at the increased methane concentrations. Nearly complete combustion was observed for both 2B+Ti fuels (nanocomposite and blended powders) at high methane concentration, when the highest rates of combustion were also observed. Thus, the effect of kinetic trap associated with formation of HOBO could not be detected. It was concluded that nanocomposite 2B+Ti powders enable one to achieve rapid and highly efficient combustion in both dry and wet gaseous environments.