Study on exergy recovery in hybrid vehicles via wastegate losses

Abstract

Vehicle hybridization is considered a promising alternative for pollutant emission mitigation. This type of vehicle combines the use of an internal combustion engine and electrical power. One of the most common layouts is the series-parallel hybrid vehicle, which consists of using a combustion engine as the main source of power in parallel to electrical sources. Besides propelling the vehicle, the combustion engine has the task of supplying energy to the electrical system. In parallel to hybridization, other technologies such as engine downsizing via turbocharging have been adopted to increase thermal efficiency of internal combustion engines. The purpose of this work is to analyze the viability of combining aforementioned technologies. To improve energy utilization, part of the exhaust system energy is recovered from a free turbine connected to the vehicle's battery. To evaluate the proposal viability, experimental data was obtained from a turbocharged spark-ignition engine. Efficiency indexes were calculated based on exergetic analyses for the turbocompressor set and the entire engine system. Thereafter, a virtual free turbine was added, assuming that it operates exactly as the main turbine and the efficiency indexes were recalculated as absolute values of recovered energy. The free turbine recovers up to 1.2% of fuel exergy and increases power by almost 5.2% at full load conditions.