can i do a two tier cake without dowels supporting the second tier- or would it simply never work
Don't risk it. Definitely put the supports in.
I certainly would not. Cake will not support cake and you are headed for disaster if you don't add supports. I don't use dowels though, I use wide straws. Most people that use straws use Bubble Tea Straws but I can't get them in my area. I have a couple of tiered cakes in my photos and I used wide drinking straws in all of them. And you'll also need to have your top tier on it's own cakeboard as well.
Cakes need support every 4 vertical inches.