Assuming you mean that's a CRLF sequence in the text node (and not merely a literal backslash-r-backslash-n), you won't be able to persuade an XML serialiser to write them as
, because XML says you don't have to. The document is absolutely equivalent in XML terms, whether you escape it or not. The only place you need to escape the CRLF sequence as
is in an attribute value.
If you really must produce this output, you would have to write your own XML serialiser that followed special rules for escaping control codes. But if you are doing this because an external tool can't read the XML element with CRLF sequences in, you should concentrate on fixing that tool, because if it can't deal with newlines in text content it's broken and not a proper XML parser.