Heavy-duty diesel (HDD) engines are the primary propulsion source for most heavy-duty vehicle freight movement and have been equipped with an array of aftertreatment devices to comply with more stringent emissions regulations. In light of concerns about the transportation sector's influence on climate change, legislators are introducing requirements calling for significant reductions in fuel consumption and thereby, greenhouse gas (GHG) emission over the coming decades. Advanced engine concepts and technologies will be needed to boost engine efficiencies. However, increasing the engine's efficiency may result in a reduction in thermal energy of the exhaust gas, thus contributing to lower exhaust temperature, potentially affecting aftertreatment activity, and consequently rate of regulated pollutants.This study investigates the possible utilization of waste heat recovered from a HDD engine as a means to offset fuel penalty incurred during thermal management of SCR system. Experiments were aimed at conducting detailed energy audit of a MY 2011 heavy-duty diesel engine equipped with a DPF and SCR. A MATLAB® based steady-state simulation tool was developed to simulate a waste heat recovery system (WHRS) based on an Organic Rankine Cycle (ORC), working with three different organic fluids, and primarily harvesting energy from combinations of the engine's heat dissipating circuits. The simulations were based on experimental data obtained through a comprehensive characterization of engine energy distribution using a heavy-duty engine dynamometer.Results obtained from the ORC-WHRS simulation over the engine operating points showed that the working fluids, R123 and R245fa with utilizing post-SCR exhaust stream, and exhaust gas recirculation (EGR) cooler as the two heat sources provided the optimum performance. As the primary goal of this study was to understand the utilization of a WHRS as a strategy for thermal management of an after-treatment system in reducing NOx levels, the study further investigates into the dynamic operation of a heavy-duty diesel engine from an actual vehicle testing. Assessment on magnitude of the energy generated for the transient vehicle operation does show ORC-WHRS as a feasible application in reaching the desired thermal state of a typical HDD engine SCR system.