Hybrid Turbocharging for Alternatively Fueled Internal Combustion Engines in Naval Applications

Abstract

The global shipping industry is at a crucial juncture, facing an urgent need to reduce greenhouse gas emissions in the short to medium term to mitigate climate change. A shift towards alternative fuels is imminent, necessitated by the limitations in current fuel cell and battery technology in terms of power density. Addressing this, navies worldwide are not only exploring the use of alternative fuels to diminish environmental impact but also seeking solutions to reduce emissions signatures and decrease reliance on fossil fuels. In this paper, we investigate the use of hybrid turbocharging to improve the dynamic performance of alternatively fueled combustion engines. We extended an existing and validated Mean Value First Principle (MVFP) engine model of a spark-ignited (SI) throttle-controlled Caterpillar 3508A gas engine with a hybrid turbocharger. The study investigates the impact of electrical power Power-Take-In/Off from the turbocharger shaft on the engine’s air path dynamics for different use cases, considering transient and steady state phases. We demonstrate that a generator set can benefit from hybrid turbocharger by significantly reducing the engine speed drop and settling time after a load step. While accelerating from 0 to cruise speed, propulsion engines benefit less from hybrid turbocharger, due to risk of compressor surge during low engine speeds. The overall results show that simply adding electric power to the turbocharger shaft during transient phases does not unlock the full potential of hybrid turbocharging for alternatively fueled combustion engines. The implementation of hybrid turbocharging requires careful integration, reconsideration of sizing and matching of turbine and compressor, and the combination with blow-off, blow-by, and waste gate valves to prevent compressor surge. However, the capability for electrical power take-off/in within a larger propulsion and electrical power generation plant context suggests a reduction in spinning reserves and an increase in overall system efficiency during steady state. Thus, implementing hybrid turbocharging can play an important role in the transition to alternative fuels and the reduction of greenhouse gas emissions.