Abstract
Waste heat recovery from passenger car internal combustion engines by means of an organic Rankine cycle (ORC) system is promising for reducing CO2 emissions. In this study, different cycle configurations capable of converting waste heat from both coolant and exhaust gases are investigated based on different working fluid categories. Radial-inflow turbines are considered as expansion devices and corresponding isentropic efficiencies are evaluated based on a preliminary design map accounting for the effect of the pressure ratio. Mechanical losses resulting from the use of a gas-bearing-supported rotor driving a permanent magnet generator are also evaluated. In order to identify the turbo-ORC system design tradeoffs, constrained multi-variable and multi-objective optimizations are performed using an evolutionary algorithm. It is found that the optimal cycle configuration and working fluid depend on the available space in the vehicle and that the condenser is the most critical component for the ORC system integration. In addition, the most suitable working fluids for this application are characterized by (1) a boiling point close to the heat sink temperature, (2) a high critical pressure, and (3) a high molecular weight. The resulting optimal radial-inflow turbines are 10–33 mm in tip diameter and operate at 80–330 krpm.
Highlights
35 Growing concerns about fossil fuel shortage and global warming advocate for a more rational use of primary energy
In the European Union, passenger cars account for 87% of the total road vehicle fleet
40 while producing 64% of the associated CO2 emissions [3]. These high levels of emissions result from the low fuel-to-wheel efficiency of vehicles propelled by internal combustion engines (ICE), i.e. typically 15-31% [4]
Summary
35 Growing concerns about fossil fuel shortage and global warming advocate for a more rational use of primary energy. The transportation sector consumes 20% of the worldwide primary energy supply, while depending mainly (92%) on fossil fuels [1]. As a consequence, this sector is responsible for 24% of the worldwide CO2 emissions from fuel combustion, including 75% from road transports [2]. 40 while producing 64% of the associated CO2 emissions [3] These high levels of emissions result from the low fuel-to-wheel efficiency of vehicles propelled by internal combustion engines (ICE), i.e. typically 15-31% [4]. There is a strong potential for energy savings and emission reductions by improving the efficiency of ICE-powered road vehicles. Such improvements can be achieved by (1) decreasing the vehicle power requirements, (2) improving the efficiency of the power
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