But before you came in here asking for info did you even attempt a search for what you're looking for? And if you did, were the right spellings used?
Defuser = Diffuser
This forum has plenty of info on the EBD so take a moment to find it if you really want it. Most of our members are more than willing to help out but at least do your part and take the first steps instead of demanding info right off the bat.
My feeling in this case (because its a complicated part), if you don't know anything about it, then leave it off the car.
Also, your design process is backwards. You should start with a problem and form a solution. Here you got the solution (exhaust blown diffusor) but no problem. The design judges will likely (attempt to) kill you for this.
And another thing. The blown diffusor is not new. Not even in FSAE/Student. I remember a NZ FSAE team had exhaust outlets fed into their diffusor in about 2005.
maybe I´m a bit naive..but not much in formula student/SAE in common with f1(open 4 wheeler)...but much more degree of freedom in the regs. You could make your life even harder and look for ideas in supertouring or truck racing as well...? again provocative but as tim put it you need to define your goals first and then start to develop and look how you can achieve the set targets .I would not even call this problems.
@ marcush: I think our original poster has been somewhat misunderstood. He's refering to a "Blown De-fuser", meaning a broken device for the de-fusing of different situations, not an a "Diffuser" in the aerodynamic sense. Big difference that.