Transient characteristic evaluation and optimization of supercritical CO2 Brayton cycle driven by waste heat of automotive gasoline engine

Abstract

Under the severe situation of low energy efficiency and strict emission standards, waste heat recovery, is considered to be a feasible technology, to achieve fuel economic in automobile industry. Among them, supercritical CO2 Brayton cycle has become one of the most promising technology owing to its high efficiency and compactness. Besides, the exhaust temperature and flow of automobile engine change dramatically in practice, resulting in a negative impact on the thermodynamic performance of the power cycle. Therefore, this paper develops a dynamic model of waste heat recovery system, carries out operating parameters analysis, transient response characteristics research and performance optimization, and finally proposes an improved method to adjust turbine inlet temperature to obtain higher output power. The change trend displays that the influence of turbine inlet pressure on thermodynamic performance is opposite to the dynamic response characteristics, and similar results also occur under engine start-up conditions. The numerical results indicate that the optimized output power and electric production cost reach 2.97 kW and 0.38 USD/kW·h, compared with the previous method, an improvement of 3.48% and 5.00% are achieved, respectively, reflecting the significance of energy conservation and emission reduction.