If you are just learning IT security then you should first learn the definitions of
SQL Injection Attack
before asing the question. ASCII is a mapping of bit patterns onto characters (EBCDIC and unicode are two others). SQL injection is a method of embedding unwanted (to the atackee) SQL commands in other legitimate commands. It is independent of the character encoding.
You are not protecting yourself by using a different delimiter. You protect yourself (one way) by using parameterized queries. For example, if you have a textbox on a form where a user is building a search query and the user is expected to type in a field to search for, let's say a last name, with the resulting query something like
SELECT * FROM someTable WHERE last_name = 'Jones'
where Jones is entered by the user. What would happen if instead of entering Jones, the user entered Jones'; drop table someTable. In that case the resulting query would be
SELECT * FROM someTable WHERE last_name = 'Jones'; drop table someTable
I may not have the syntax exactly right but you get the idea.