Theoretical research of carbon dioxide power cycle application in automobile industry to reduce vehicle’s fuel consumption

The current work discusses means to utilize low-grade small-scale energy in vehicle exhaust gases, to reduce the vehicle’s fuel consumption and to make it run more environmental friendly. To utilize the energy in the exhaust gas, a CO2 bottoming system in the vehicle’s engine system is proposed. Several basic cycles—according to the different design concepts—are presented, and the efficiencies are calculated using Engineering Equation Solver (EES). Several thermodynamic models in EES show that after system optimization, in CO2 Transcritical power cycle with a gas heater pressure of 130 bars and 200 °C expansion inlet temperature, about 20% of energy in the exhaust gas can be converted into useful work. Increasing the pressure in the gas heater to 300 bars and with same expansion inlet temperature, about 12% of exhaust gas energy can be converted. When raising the pressure both in the gas cooler and in the gas heater, the cycle runs completely above the critical point, and the efficiency is about 19%. Besides, in the CO2 combined cycle, the system COP is 2.322 and about 5% of exhaust gas energy can be converted.