I can decide accurately which to use in a given context, but I can't make out the actual difference in definition between "special" and "especial". I have searched two authoritative dictionaries to no avail.
In every use, especial can be replaced by special with no change in meaning. The word special does have some meanings especial does not have, such as "of or relating to a species" and as a euphemism for handicapped. Also, the phrase a special to mean an unusual offer or deal has no corresponding form with especial.
I agree with all that David Schwartz wrote in his answer. However, I think someone should tell you that almost nobody uses the word "especial." See this NGram of special vs. especial, corpus English, 1800-2008. (The NGram looks similar for both British English and American English.)
I think especial sounds affected. Can you give us an example of a sentence in which you think you might use it?