Ethanol from grass is difficult, it takes expensive enzymes to get the cellulose to break down. Yeasts are like kids, they like simple sugers, not locked up inside vegetables.
It would be easier to make biogas with a digester. Biogas is a mix of methane, carbon dioxide, and hydrogen. It comes from bacterial composting, not from fermenting with yeast, like ethanol.
It works better if the grass first goes through a sheep, chicken, goat, or cow to get the plant breakdown process going. It is pretty easy to convert an engine to run on biogas, but your horsepower rating will likely drop by about 1/4.
Mother Earth Magazine has some online articles about it. Just search the archive. Here is a link to some books that can also get you started:
KP