Turbocharged diesel engines are popular propulsion systems for automotive applications like trucks or passenger cars because of their high efficiency and advantageous torque characteristic. The high NOx emissions due to their combustion process and missing three-way catalyst are, however, a disadvantage. Consequently, to satisfy future emission legislations, NOx emissions must be reduced. In addition, growing environmental awareness requires reduction of CO2 emissions, respectively, consumption. Hybridization is an effective method to achieve these multiple goals.The general tendency in direction of electrification of the powertrain leads to a diversity of drive concepts. In this context, the study of the entire system is as important as the analysis and evaluation of the interaction of the system components. The development of an intelligent control strategy managing the different operating states like stop/start, braking energy recuperation, load point shifting and electric driving is fundamental, too. Simulation is a powerful tool for these purposes and allows exploring different configurations of powertrains without cost-intensive and time-consuming production of prototypes. An appropriate approach to improve the accuracy of the results is the replacement of a virtual component in the simulation model by real hardware (Engine-in-the-Loop EIL). Thus, the real diesel engine is in interaction with the virtual powertrain and both operate in real time. A closed loop control is created where real hardware operates with virtual model components via defined interfaces.This paper shows how at the Institute for Powertrains & Automotive Technology (IFA) of the Vienna University of Technology intelligent control strategies were developed enabling the reduction of NOx emissions by up to 35% and the consumption by up to 15% by means of a parallel diesel-hybrid powertrain. Furthermore, different hybrid powertrain concepts were analyzed with the aim of demonstrating their advantages and disadvantages concerning the achievement of these goals. In this context, the method of the EIL simulation, used to obtain a high accuracy of the results, is described as well.