Numaligarh Refinery Limited(NRL) has started supplying BSVI-grade petrol and diesel, the company said on Thursday.The NRL has began the supply ahead of schedule so that oil marketing companies can upgrade the inventory of automotive fuel at their retail outlets and terminals well ahead of the timeline, it said.The NRL had commissioned the Diesel Hydro Treater (DHDT) plant in 2018 at a cost of around Rs 1,000 crore.It also invested around Rs 125 crore for revamping its motor spirit plant to meet BSVI specification of petrol and commissioned it in January.