Response characteristics of combustion pressure exponent of propellants: compensation effect of three energetic potassium lead complexes with Co, Cu, Ni

The intense exhaust plumes of the CMDB propellants can be suppressed by the containing potassium salts, but the potassium compounds increased remarkably the combustion pressure exponent of propellants, destroying the combustion plateau effects and resulting in the combustion instability of the rocket motors, so it is critical to reveal the reaction mechanisms of the potassium salts during the combustion process of propellants. In the work, the influence of three potassium hexanitro complexes, K2Pb[M(NO2)6] (M = Co, Cu, Ni), on the ignition and combustion properties, especially pressure exponent, of solid propellants has been investigated by using the laser ignition apparatus, burning rate instrument, combustion wave temperature, flame morphology, quenched surface, and emission spectrometer. When the hexanitro complexes replaced the β-Pb, the ignition delay time of the propellants was shorter at the low laser flux. The study on the combustion properties showed that the burning rate and pressure exponent of propellant containing K2Pb[Cu(NO2)6] was extremely close to the basic propellant (β-Pb) due to similar temperature gradient until 1942 °C. The flat combustion cross section on the flame morphology of the propellant containing K2Pb[Cu(NO2)6] was found to favor the low-pressure exponent. The carbon skeleton, metal agglomerations, and K release identified by using the quenched surface and emission spectra were closely related to the response characteristics of the combustion pressure exponent of the propellants due to the influence of different hexanitro complexes. The relationship between the burning rate of the propellants and the maximum self-heating rate of the mixtures containing the propellant energetic oxides and hexanitro complexes was also revealed, which can predict the relative burning rate for the same propellant system. More importantly, the reasons for the deterioration of the combustion pressure components due to flash suppressors were elucidated clearly from the experimental results and theoretical analysis, which involve three destroying mechanisms: (i) catalytic metals “poison,” (ii) carbon skeleton disappearance, and (iii) high thermal decomposition temperature of potassium compounds. The study also revealed the inhibition mechanism of potassium flash suppressors on the catalytic properties of catalysts during the combustion process of the CMDB propellants. The influence of three potassium hexanitro complexes on the ignition and combustion properties of solid propellants have been investigated, and the reasons for the deterioration of the combustion pressure components due to flash suppressors were elucidated clearly.