AP/HTPB-composite propellants are widely used in the field of energetics due to their burning rate controllability using a variety of formulation variables. At higher pressures, the burning rate becomes less controllable as it experiences a transition regime often referred to as an “exponent break” typically between 20.7 and 34.5 MPa. The pressure exponent drastically increases to values greater than 1, making the burning rate extremely sensitive to pressure fluctuations. This study systematically evaluated the effects of catalysts on the exponent break and high-pressure burning rates of AP/HTPB-composite propellants containing a variety of AP particle sizes, distributions, and concentrations. The burning rates of seven formulations with varying AP characteristics and either Mach I iron oxide or titania nanoparticles or in-situ titania as a catalyst were evaluated between pressures of 6.89 MPa and 68.9 MPa. All formulations with the exception of two, 46.0-µm AP with Mach I titania and 138.9-µm AP with 0.50% in-situ titania, showed an exponent break. For the others, the characteristic pressure where the exponent break occurred changed with the inclusion of the catalysts, increasing it to 34.5 MPa and higher. The characteristic pressure was found to be dependent on the corresponding baseline burning rates, occurring where the additive burning rate curve intersected with its respective baseline burning rate curve. Additionally, all the burning rates fell above the AP deflagration rate curve, corroborating the existence of an AP barrier and the general theory in the literature that AP decomposition dominates in the very-high-pressure regime. This study adds new data to the severely limited database for very-high-pressure, AP-based, composite propellant burning rates in the open literature and provides one of the first fundamental studies on the exponent break feature with emphasis on the role of mixture variables and catalytic additives on the characteristic break pressure and the post-break pressure exponent.

AP / HTPB复合推进剂由于使用多种配方变量可控制燃烧速率，因此在能量学领域得到了广泛应用。在较高的压力下，燃烧速率变得难以控制，因为它经历了通常称为“指数断裂”的过渡过程，通常在20.7至34.5 MPa之间。压力指数急剧增加到大于1的值，使燃烧速率对压力波动极为敏感。这项研究系统地评估了催化剂对包含各种AP粒径，分布和浓度的AP / HTPB复合推进剂的指数破坏和高压燃烧速率的影响。七个具有不同AP特性的配方以及Mach I氧化铁或二氧化钛纳米颗粒或在6.89MPa和68.9MPa的压力之间评估了原位二氧化钛作为催化剂。除两种配方外，所有配方均为两种：46.0​​ µm AP和Mach I二氧化钛和138.9 µm AP，原位0.50％二氧化钛显示出指数断裂。另外，随着催化剂的加入，发生指数破坏的特征压力发生变化，使其达到34.5MPa以上。发现特征压力取决于相应的基线燃烧速率，这发生在添加剂燃烧速率曲线与其各自的基线燃烧速率曲线相交的地方。此外，所有燃烧速率均高于AP爆燃速率曲线，从而证实了AP屏障的存在以及文献中的一般理论，即在非常高压的情况下AP分解起主导作用。这项研究将新数据添加到了非常有限的基于AP的非常高压数据库中，