Why do stars consume fuel the way they do?

A star like our sun has a convective zone outside the core, but the core itself is not part of this. So the heavy helium does accumulate in the core. But still, the core is hot enough to fuse hydrogen (15,000,000 kelvin) but not helium (which needs 100,000,000 kelvin).

The temperature change with distance from the center is too low to drive convection, so the hydrogen just sits there. Eventually, in another 4 or 5 billion years, the helium concentration will be high enough to stop the hydrogen fusion in the core. Then layers above to core will be able to sink down, compress, and start hydrogen fusion higher up.

Well, it starts fusing hydrogen because that's the easiest element *to* fuse.... Most of the make-up of a star is hydrogen (or, at least, our sun), and only has a very small core of helium.

Even 2nd and 3rd generation stars are primarily hydrogen. Only the core of a star is hot enough with high enough pressure to convince positively charged hydrogen nuclei to fuse. Larger nuclei have higher positive charge, so required higher temperatures to fuse.

That's a very good question, I never thought about that.

I can only assume that since the density of the core is about 150 times that of water that the hydrogen is not able to move about so freely and currents keep things moving around. totally a layman answer

http://en.wikipedia.org/wiki/Sun

Actually the deuterium goes first, but there isn't much of it.