Prognostic humidification management for energy-optimal vehicular fuel cell systems under lower heating value conditions

초록

This study proposes a prognostic operational framework based on lower heating value (LHV) conditions for energy-optimal management of vehicular fuel cell systems. Conventional empirical or feedback-based humidification strategies usually prescribe inlet relative humidity (RH) without predicting the physically required target, and the system-efficiency benefit of LHV-consistent operation has not been clarified under high-current conditions. To address these gaps, the proposed framework determines the required inlet RH in advance by imposing outlet saturation as a vapor-phase water-removal constraint. Quantitative models are developed by introducing a net water transfer coefficient and a net heat transfer coefficient, which describe the partitioning of generated water and heat between the anode and cathode channels. The proposed coefficients are validated against published experimental data with strong agreement, confirming their predictive capability. The framework further incorporates major balance-of-plant subsystems, including fuel processing, air processing, thermal management, a shell-and-tube membrane humidifier, and a centrifugal air compressor. Physics-based sub-models are established to describe heat and mass transfer processes governing system-level humidity, pressure, and temperature distributions. Results indicate that the prognostic strategy predicts a required cathode inlet RH of 22% under reference conditions. Higher current density, higher inlet pressure, lower coolant temperature difference, lower stoichiometric ratios, and humid ambient environment reduce humidification demand. Moreover, comparison with a fixed-humidification baseline demonstrates that LHV-consistent operation improves estimated net system efficiency in the high-current region by suppressing liquid–water formation, reducing heat generation, and lowering parasitic power. The proposed framework establishes a physics-based operating paradigm for energy-optimal fuel cell system management.

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