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ISSN Online: 2150-7678
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CHARACTERIZATION OF THE THERMAL BEHAVIOR OF A PROPELLANT INCREMENT DURING TRANSPORT AND STORAGE
ABSTRACT
This study characterizes the thermal behavior of a propellant increment of a mortar exposed to a variety of thermal environments and packaging configurations that are common during the storage, transport, and inspection of munitions. A mortar is a projectile that is fired by dropping it into a tube and striking a percussion primer on a firing pin at the bottom of the tube. A propellant increment is the portion of a propelling charge that can be removed from the mortar assembly to adjust the velocity of the mortar as it exits the mortar tube after being fired. The performance of the propellant is driven by the resulting pressure profile within the weapon system once it is ignited, which is driven by the burn rate. The burn rate is based on the chemical properties of the propellant as well as the temperature distribution and average bulk temperature of the propellant within the increment. The performance of the propellant is observed through the distance the mortar travels after being fired and the flight stability of the munition, which in extreme cases can cause erratic flight. This study is divided into two parts, with an overall goal of developing a predictive capability to estimate the temperature response of a propellant increment over several scenarios. First, a prototype numerical model is developed using known material properties that match an expected response. Second, experimental data is collected in a format and frequency that supports validation of the numerical model. The experimental data collection focuses on monitoring temperature response at discrete points within the volume of an increment over several heating and cooling scenarios in a controlled laboratory oven. The laboratory oven enables the control of external factors, and the numerical model accounts for variations of thermal solar loading, packaging configuration, and orientation.
Ideally, a method would allow for the estimation of the bulk temperature of an increment, but results indicate that while there are regions of the volume of propellant that approximate the bulk temperature within 10%, these regions are not constant across scenarios, and without a priori knowledge, the location of these regions in each scenario cannot be estimated accurately. Additionally, perforating the shell of the increment creates a safety hazard and potential performance degradation, and the surface of the increment does not provide a reliable estimate of the bulk temperature of the propellant in most scenarios studied. More in-depth analysis, most likely with a priori knowledge of the historical temperature distribution within the propellant itself, is needed to provide a more reliable estimate of the temperature distribution and bulk temperature of the increment.
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