Compression ignition engines are the most efficient among the internal combustion engines. This diesel engine also gives inferior aspects of contaminants like carbon monoxide and unburned hydrocarbons. Nevertheless, the significant parts to deal with the diesel engine is its relatively higher emission of NOx which needs evolution and improvement of the engine to minimize NOx apart from CO & HC emissions. In the lean engine operation, the diesel engine demands innovative emission reduction techniques than the staandard operation engines. The selective catalytic reduction would be a more significant trigger in reducing nitric oxide entering the atmosphere from automobiles. The catalyst in the SCR is to decompose the nitric oxide and promote chemical reduction with a supplementary reducing agent to exhaust gas, even at lower temperatures. The most promising catalyst is copper ion-exchanged zeolite. This project exhibits the design and development of a urea injection system and a catalytic converter to control NOx emission in the lean operating diesel engine. By pre-oxidizing the emission, there is a reduction of 1.2% of hydrocarbon and 33% carbon monoxide. Fortunately, the increase in the carbon dioxide emission by 3.9% shows a positive result on oxidation reaction. The higher amount of oxygen resulted in increased nitrogen by 15% in the full load operations. © 2023 Elsevier B.V., All rights reserved.