Objectives For the economic and environmental requirements of polar ice-breakers, a hybrid propulsion system composed of diesel generator sets and a rechargeable battery is proposed.

Methods First, the resistance model is established on the basis of ice scale, and the energy flow model of the diesel/battery hybrid propulsion system is established using the inverse simulation method. The component parameters of the propulsion system are then optimized on the basis of an elitist nondominated sorting genetic algorithm-II (NSGA-II) with "annual fuel consumption" and "total cost of entire life cycle" as the optimization objectives, and the optimal design is obtained via the technique for order of preference by similarity to ideal solution (TOPSIS) method. Finally, the sensitivity analysis of the optimization objectives to seven design parameters is conducted.

Results The results show that the optimal design scheme of the diesel/battery hybrid propulsion system can save 1.89% in fuel consumption compared with the traditional diesel-electric propulsion system, and the pure electric navigation time accounts for 31.22% of the whole voyage, but the rechargeable battery reduces the economy of the system. The sensitivity analysis shows that the optimization objectives ("annual fuel consumption" and "total cost of entire life cycle") of the hybrid propulsion system are sensitive to main engine capacity, number of battery packs and battery state of charge, while less sensitive to reducer ratio, motor capacity and propeller size.

Conclusions The results of this study can provide references for the research and design of polar icebreakers and other diesel/battery hybrid electric ships.