Collaborative optimization of exhaust gas recirculation and Miller cycle of two-stage turbocharged marine diesel engines based on particle swarm optimization

Abstract

To meet increasingly stringent emission standards and lower the brake-specific fuel consumption (BSFC) of marine engines, a collaborative optimization study of exhaust gas recirculation (EGR) and a Miller cycle coupled turbocharging system was carried out. In this study, a one-dimensional numerical model of the EGR, Miller cycle, and adjustable two-stage turbocharged engine based on WeiChai 6170 marine diesel engine was established. The particle swarm optimization algorithm was used to achieve multi-input and multi-objective comprehensive optimization, and the effects of EGR-coupled Miller regulation and high-pressure turbine bypass regulation on NO_x and BSFC were investigated. The results showed that a medium EGR rate-coupled medium Miller degree was better for the comprehensive optimization of NO_x and BSFC. At medium EGR rate and low turbine bypass rates, NO_x and BSFC were relatively balanced and acceptable. Finally, an optimal steady-state control strategy under full loads was proposed. With an increase in loads, the optimized turbine bypass rate and Miller degree gradually increased. Compared with the EGR-only system, the optimal system of EGR and Miller cycle coupled turbine bypass reduced NO_x by 0.87 g/(kW·h) and BSFC by 17.19 g/(kW·h) at 100% load. Therefore, the EGR and Miller cycle coupled adjustable two-stage turbocharging achieves NO_x and BSFC optimization under full loads.

Keywords

exhaust gas recirculation (EGR) / Miller cycle / NO_x emissions / adjustable two-stage turbocharging / particle swarm optimization

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