Http request

Hi guys!

I need to add a value in the header of the request, called HASH and also need to change the content-type of the same. In my research I found the following:

let _header = new Header ();
_header.append ( 'Content-Type', 'application / x-www-form-urlencoded; charset = utf-8');
_header.append ('HASH', '1234567890');

this.http.post (url, params, {headers: _headers});

The problem is that the request does not go as I need ... If I remove the HASH the content-type is changed correctly, but if you add more than one property break all ...

With only the 'Content-Type'

Accept:*/*
Accept-Encoding:gzip, deflate
Accept-Language:pt-BR,pt;q=0.8,en-US;q=0.6,en;q=0.4
Connection:keep-alive
Content-Length:173
Content-Type:application/x-www-form-urlencoded; charset=UTF-8 <--- OKKKKK
Host:192.168.0.28
Origin:http://192.168.0.28:8100
Referer:http://192.168.0.28:8100/?ionicplatform=ios
User-Agent:Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/48.0.2564.109 Safari/537.36

With the 'Content-Type' and 'HASH'

Accept:*/*
Accept-Encoding:gzip, deflate, sdch
Accept-Language:pt-BR,pt;q=0.8,en-US;q=0.6,en;q=0.4
Access-Control-Request-Headers:content-type, hash <--- Wtf!?
Access-Control-Request-Method:POST <--- Wtf!?
Connection:keep-alive
Host:192.168.0.28
Origin:http://192.168.0.28:8100
Referer:http://192.168.0.28:8100/?ionicplatform=ios
User-Agent:Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/48.0.2564.109 Safari/537.36

What is wrong? Someone?