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

Abstract

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 CO 2 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). 1 The thermodynamic properties for carbon dioxide in EES are calculated by the fundamental equation of state developed by Span and Wagner, A new equation of state for carbon dioxide covering the fluid region form the triple-point temperature to 1100 K at pressures up to 800 MPa, J. Phys. Chem, Ref. Data, Vol. 25, No. 6, 1996. http://www.fchart.com/ees/ees.shtml. 1 Several thermodynamic models in EES show that after system optimization, in CO 2 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 CO 2 combined cycle, the system COP is 2.322 and about 5% of exhaust gas energy can be converted.