local to gmt function doesn't work

My server(localhost) timezone is Europe/Berlin.
I set both $config['time_reference'] = 'SGT'; and $config['time_reference'] = 'Asia/Singapore'; in config.php which is singapore time.

now I need to convert the local DateTime to GMT by using this code

PHP Code:

$local = now();
echo 'Local : '.nice_date(unix_to_human($local),'Y-m-d h:i A');
echo 'GMT : '.nice_date(unix_to_human(local_to_gmt($local)),'Y-m-d h:i A'); 


And the result will be

Code:

Local : 2017-07-11 09:33 PM
GMT : 2017-07-11 07:33 PM

But the GMT time is not correct. At this time the GMT time is 1:33 PM NOT 7:33 PM

1. by changing the $config['time_reference'] the application timezone will change?
   
2. How to check which Timezone is being used by CodeIgniter?
   
3. Is this a correct way to make use of Date helper to achieve my goal?
   
4. How can I fix this?
   

Thanks in advance