Pulse Detonation Engines (PDEs) are propulsion systems that use repeated detonations to generate thrust. Currently in early stages of development, PDEs have been theorised to have advantages over current deflagration based engines. Air-breathing PDEs could attain higher specific impulse values and operate at higher Mach numbers than today's air-breathing engines, while Pulse Detonation Rocket Engines (PDREs) could become a lighter, cheaper, and more reliable alternative to traditional rocket engines. There are still however, many technological hurdles to overcome before PDEs can be developed into practical propulsion systems, one major barrier being management of their immense heat loads. This thesis outlines the development of a numerical model for determining thrust performance and heat load characteristics of PDEs. The model is based on a set of analytical equations which characterise the gas dynamics inside the engine throughout it's cyclic process. Being numerically light -when compared to CFD analysis- the model allows for fast turnaround of results and the ability to sweep through parameters to determine optimum operating conditions to maximise engine performance and reduce heat load. In this study, the working principles of the model are described and it's outputs are validated against data from published experimental and numerical studies. The model is then used to conduct a comprehensive parametric study on the effects of various reactant combinations, operating conditions, and engine geometries on engine thrust, specific impulse and heat load. Lastly, a brief study is conducted on the feasibility of regenerative cooling for PDEs, using model outputs to determine if a heat balance can be achieved and the performance losses and complications that would result.