The combined impact on fuel economy that results from low energy density (negative impact) and higher efficiency at high engine loads (positive impact) is assessed for the series PHEV. Changes to the vehicle energy management strategy for the series PHEV are proposed based on the differences in fuel consumption for the different blends. In this study, Argonne's vehicle system simulation and control software AUTONOMIE was used to simulate the engine-in-the-loop process. This paper describes the process in the AUTONOMIE environment.