D.E.F is essential for the correct operation of an advanced pollution control technology installed in the exhaust system called Selective Catalytic Reduction(SCR). When injected into hot exhaust as a fine mist and passed over a catalyst, DEF helps convert NOx (nitrogen oxide) into nitrogen gas and water vapour-- two clean and harmless components of the air we breathe. DEF is stable, colourless and odourless. When Use in BS-IV engines it increase the diesel average by 3-4%. DEF consumption is approximately 2-3% of fuel use but varies with duty cycle, operation, geography and other factors.