Mechanisms of Confined Explosions and The Effects of Afterburn – The Consistency of Experimental Measurement and Thermochemical Prediction.

Developing an improved understanding of explosions occurring in confined spaces is becoming of increasing importance. This is due to the increase in storage silo explosions and ammunition store development and the need to ensure that accidental explosions in these situations can be minimised in terms of effects or risk of occurring. To gain a better understanding of these scenarios, there have been investigations into the confined environments, but with differing conclusions about the repeatability and processes occurring in these confined environments.
A testing regime and methodology was created for this thesis to allow confined experiments to be conducted, investigating the consistency of explosive events and the ability to measure the quasi-static pressures generated. These pressures are generated post initial shock pressures generated by the explosion due to build up of pressure in the system from an increased temperature in the confined space and gas formation increasing the amount of gas in the system. This causes an increase in overall pressure over a longer timeframe in the order of seconds. Using differing masses of explosive in the same volume of confined chamber, a profile for consistency was generated which shows considerable levels of repeatability. Following developing this experimental method, an infra-red thermometer was used to determine the temperatures generated in an explosive event and compared to the ideal gas equation to determine if the assumptions would hold.
A thermochemical model was then generated using the ideal gas equation, predicting the pressures generated in a confined explosion using a chemistry-based approach. This model allows the prediction of maximum quasi-static pressures (QSP) accurately for the charge to volume ratios tested. This model was then tested rigorously by investigating other scenarios such as altered explosive types as well as altered surrounding atmospheres in the chamber, to investigate if the model could cope with other conditions.
These trials were then investigated to understand the processes occurring during the early stage of the explosive event as well as the late time effects such as energy loss through heat transfer. This provided a better understanding of the explosive process and an insight into future work that could be performed in this field.
This leads to a thesis that can be used to show that improvements need to be made in the field of confined explosive measurements and modelling, before outlining and developing the ways to start that process and the impact they could have on the future of this subject.