Exergo-Technological Explicit Selection Methodology for Vapor Cycle Systems Optimization for Series Hybrid Electric Vehicles

Abstract

Significant research efforts are considered in the automotive industry on the use of low carbon alternative fuels in order to reduce the carbon dioxide emissions and to improve the fuel economy of future vehicles. Some of these fuels, such as the solid fuels for example, are only compatible with external combustion machines. These machines are only suitable for electrified powertrains relying on electric propulsion, in particular series hybrid electric vehicles (SHEV) where fuel consumption strongly relies on the energy converter performance in terms of efficiency and power density, as well as on the deployed energy management strategy. This paper investigates the potential of fuel savings of a SHEV using a vapor cycle machine (VCM) system as energy converter substitute to the conventional internal combustion engine (ICE). An exergo-technological explicit analysis is conducted to identify the best VCM-system configuration. A Regenerative Reheat Steam Rankine Cycle with condenser reheat and turbine reheat (RReCRTRe-SRC) system is prioritized, offering high efficiency, high power density and low vehicle integration constraints among the investigated systems. A plug-in SHEV model is developed and energy consumption simulations are performed on a worldwide-harmonized light vehicles test cycle (WLTC). Dynamic programing is used as global optimal energy management strategy. A sensitivity analysis is also carried out in order to evaluate the impact of the battery size on the fuel consumption. Fuel consumption simulation results are compared to ICE on same vehicle powertrain. Results show +2% to +3.5% additional fuel consumption, on self-sustaining SHEV, with the RReCRTRe-SRC as auxiliary power unit (APU) compared to ICE. Consequently, the selected VCM-APU presents a potential for implementation on SHEVs with zero carbon alternative fuels.