Unhappy with my PHD CS research topic. What should I do?
In general, a proof or demonstration that something does not work for a particular application can be as valuable as proving that something does work. This is especially true if a priori, the thing should seem to work. 

You might explore with your advisor whether this is a viable direction for your work to take. I can't predict what he/she would say, but it is worth spending some time in the exploration before you bail out. You probably have some deep insights into the problem that you can bring to bear. 

Again, research is about knowledge, not about doing some inappropriate thing just to "force" it to kind of work. Extract the knowledge from the project. 

But your advisor is likely the final judge here.