Question: I am trying to send email to a Lotus Notes group from a Lotus Notes application, But email is sent to Outlook group with same name. Is there any way that email be sent to LN group not to exchange group.

Here LN is not used for mailing anymore. It is done by Exchange.

Answer: 
Yes this is possible. Making a few assumptions about your setup it sounds like at one of our clients. Domino is used for apps but exchange for email, with domino routing mail via exchange.
The the domain is something like xyz.com then sending a mail to "MyGroup" will go to MyGroup.xyz.com and via exchange.
To send just to domino you need to use the Local primary Internet domain which is configured under the Messaging\Domains section in server config on Conversions tab. In our case it's domino.xyz.com so sending a mail to mygroup@domino.xyz.com would go to domino and not routed to exchange
Set your Notes group's type as 'Access Control List' only, so it won't be considered a mailable name.