Voluntary and enthusiastic

I think I need a new word. I'm trying to describe my hope that project participants and client volunteers have two qualities. They need to be enthusiastic, in that they are positive and encouraging and engaged regarding the project. And, enthusiasm needs to be voluntary, in that it's because of a true personal interest in intrinsic motivation, not nearly fake because of some reward or feeling of obligation.

But I think the word "voluntary" doesn't exactly capture that. As long as it's not under threat or duress, engaging in something is by definition "voluntary." So I need a word that captures something more than "I'm not doing this because anybody is forcing me to," but instead really says, "I'm doing this because I truly want to do it."

Is that a distinction without a difference, or does it make sense?