Influence of shaft motor/generator on dynamic behavior of natural gas/diesel dual-fuel engine in ship hybrid propulsion system under various operating conditions

To reduce shipping emissions, natural gas is a viable alternative fuel for marine engines. However, natural gas (or natural gas/diesel dual-fuel) engines exhibit poor dynamic performance, potentially compromising ship safety in adverse conditions. The hybrid propulsion system, which consists of the main engine and shaft motor/generator (MG), can enhance the operational safety of ocean-going cargo ships. This study integrates a mean-value dual-fuel engine model into a hybrid system for a chemical tanker, analyzing dual-fuel engine’s dynamic operating range limited by thermal load, surge, knocking, and misfire. The dynamic behavior of dual-fuel engine assisted by shaft MG in different dynamic operating conditions is also investigated. Results show the shaft MG helps smooth load fluctuations, mitigates thermal load and other adverse effects, and improves engine performance. However, the MG’s effectiveness does not scale linearly with power output; it should be controlled to make the load change acceptable for the main engine.