Crafty is one of the top chess engines and completely open source. However I would discourage you from using it for a student project it's written in C, very complex and very hard to understand because it is highly optimized.
For educational purposes I would recommend taking a look at Adam Berents site where he describes the process he went through when he implemented a chess engine in C#. The source code is available as well of course. It's an excellent point to start from, in my opinion.
