Combined Cycle Gas Turbine System Optimization for Extended Range Electric Vehicles

Abstract

Due to the continuous tightening of emissions regulations on passenger vehicles, in particular beyond 2025, vehicle manufacturers are exploring several alternative energy converters to replace the conventional internal combustion engine (ICE) in electrified powertrains, for the sake of reducing the fuel consumption to levels lower than 3 L/100 km. The purpose of this study is to investigate an alternative powertrain that is more efficient and environmentally friendly to replace the conventional ICE in an extended-range electric vehicle (EREV) with a series hybrid electric powertrain configuration. The Combined Cycle Gas Turbine (CCGT) system is investigated as an auxiliary power unit of the powertrain. This machine is more suitable for an EREV application as it offers many advantages compared to the ICE, namely a reduced number of moving parts, vibration-free operation, low maintenance cost, high durability, multi-fuel use capability and mostly a quasi-stable operation at the optimum efficiency. An exergo-technological explicit analysis is firstly conducted to assess the thermodynamic performance of the simple CCGT system using the REFPROP software. Then, based on the major sources of exergy destruction in the system, a list of CCGT configurations with several thermodynamic modifications is proposed in order to identify the most suitable CCGT topology for EREV. Energy and exergy analyses are then conducted on all proposed cycles using state-of-the-art physical parameters for the CCGT components. Then, a multi-objective Genetic Optimization Algorithm (NSGA) is used to obtain a Pareto graph for each configuration, optimizing for the overall efficiency and net specific work as function of the design parameters. The reheat gas turbine combined to a turbine reheat steam Rankine cycle system (ReGT-TReSRC) is prioritized among the studied CCGT configurations, and its optimal design parameters are identified. Results show 5% to 26% of efficiency improvement with the prioritized ReGT-TReSRC as compared to the ICE, depending on the material used in the turbine, allowing to extend the turbine inlet temperature from 950°C to 1250°C.