A method of operating an internal combustion engine is provided. The method includes combusting a mixture of fresh air and fuel within multiple cylinders. The method also includes directing a first portion of exhaust gases into a first-stage turbine and a second-stage turbine of a turbocharger for expanding the exhaust gases, directing a second portion of exhaust gases from the exhaust manifold via an exhaust channel bypassing the first-stage turbine and recirculating a third portion of exhaust gases into an intake manifold after mixing with fresh air. The method includes controlling at least one of: reducing a normal engine speed at each engine power setting while maintaining constant engine power level by increasing a fuel injection per cycle; concurrently increasing a flow rate of the third portion of exhaust gas during recirculation; and advancing a fuel injection timing for reducing emission levels that meets Tier 4 requirements.