Hii Nitish..

No, you can't take admission in Delhi University after diploma in engineering.

Rather on the off chance that you needs to concentrate further, you can get admission in Delhi technological university (formely Delhi college of engineering), or Guru gobind singh indraprastha college by clearing DTU-LEET test.

You will get admission in second year of B.E/B.tech.

Hope these will be helpfull...

All the best!!