There is no information out for 2018 cut off as it varies year, category, branch and quota wise so please be specific with the same but according to previous year trend the closing rank for top branch like CS is mentioned below -

Computer Science and Engineering (2017) - 11564 (Closing Rank, HS).

Computer Science and Engineering (2016) - 11375 (Closing Rank, HS).

For reference, you can go through the below link -

https://engineering.careers360.com/articles/jee-main-cutoff-for-nit-delhi

Good Luck!!!