At Delhi Airport there are PODS, which has single and double beds for rents. They are currently at $10 per hour for single and $14 per hour for double. They are located opposite to the International departure area (near Gate 17). They cannot be booked in advance. And the business Lounge, Shower and Nap Louges too.
The other alternative is to stay at Eaton hotel.
See the below link to see more details