field_info_field: how to define the content type name?
What you're doing here seems correct to me, bear in mind that you can leave the bundle parameter empty and then you'll get an array of results keyed by bundle so you can evaluate if there's a problem with the machine name of the bundle you're using:

  $instances = field_info_instances('node');


You can also access admin/reports/fields and take a look to fields and content types available in your site.