Publishing outside of my PhD Research I am currently undertaking my PhD in a very niche sub field of Artificial Intelligence. However, I have, what I consider, a strong background in programming and often contribute to many open source projects in my spare time. I have recently started an Open Source project which solves a very particular problem, but is outside the scope of my PhD research.

I wish to publish my hobby research and I doubt this is something my project supervisors, or university would be interested in. Should I go ahead and publish without their knowledge, or should I ethically bring it to their attention before I send it off? It should be noted, because it is my hobby project, I don't particularly want it influenced by an academic agenda.
This is something that you need to discuss specifically with your advisors. They may or may not be interested in the publication—but they may also have an interest in ensuring that your goal of publishing doesn't interfere with your paid work. (For instance, spending a lot of time editing your "hobby" manuscript when you should be working on your talk for an upcoming conference for your "paid" project.)

You should also check with your university's intellectual property office about the guidelines for such work. So long as you're doing things on your own without university assistance or resources, there might not be a problem. But if you need to use equipment owned by them to produce your idea, things might change.