Flame structure of wide distribution AP/HTPB composite solid propellants from emission imaging

Experiments investigating the flame emission of four AP/HTPB composite propellants (three widedistribution bimodal propellants, one fuel rich monomodal propellant with only fine AP) have been performed. Time dependent spectral data and filtered emission images were acquired during the experiments, in combination with pressure traces. The spectral data shows that the addition of a transition metal oxide to the bimodal formulation significantly increases the broadband emission in the range of 210-460 nm. Excited OH radical emission is distinguishable for the bimodal formulations for pressures from 100-900 psi (0.7-6.2 MPa). Emission images acquired with an intensified CCD camera, with a 310 nm bandpass filter (10 nm FWHM), showed a nearly linear dependence of intensity on pressure. Spatial structure was largely thought to be the result of nonpremixed flame conditions. Several time dependent emission fluctuations were observed. One bimodal mix demonstrated strong intermittent burning with a time scale on the order of 1 Hz in tests at 900 psi. A “matrix” type formulation (binder rich composite with only fine AP) showed a 250 Hz fluctuation in tests at atmospheric pressure.