自動車工学の進歩
オープンアクセス

概要

On-Board Cold Thermal Energy Storage System for Hydrogen Fueling Process

Young Min Kim

The hydrogen storage pressure in fuel cell vehicles has been increased from 35 MPa to 70 MPa in order to accommodate a longer driving range. On the downside, such pressure increase results in significant temperature rise inside the hydrogen tank during fast filling at a fueling station, which may pose safety issues. Installation of a chiller often mitigates this concern because it cools the hydrogen gas before its deposition into the tank. To address both the energy efficiency improvement and safety concerns, this paper proposed an on-board cold thermal energy storage (CTES) system, cooled by expanded hydrogen. During the driving cycle, the proposed system uses an expander, instead of a pressure regulator, to generate additional power and cold hydrogen gas. Moreover, CTES is equipped with phase change materials (PCM) to recover the cold energy of the expanded hydrogen gas, which is later used in the next filling to cool the high-pressure hydrogen gas from the fueling station. A few years ago, the typical hydrogen storage pressure in fuel cell vehicles was 35 MPa; such pressure produced a very low volumetric energy density to accommodate long-range driving that would require 70 MPa. Recently, on-board hydrogen storage, mainly in high pressure of 70 MPa, has been widely adopted. This increase of pressure, however, leads to a significant rise in the temperature of the vehicle tank during fast filling at a fueling station due to heat of compression and Joule–Thomson expansion. Pre-cooling hydrogen with a chiller before refueling mitigates the temperature rise to meet the maximum allowable tank temperature that conforms to international standards and regulations such as the Society of Automotive Engineers (SAE) protocol and the International Organization for Standardization (ISO) safety code (i.e., 85 °C). Such temperature rise during the filling process also reduces the total amount of gas stored inside the tank. In a series of experiments, Kim et al. quantified temperature change on the cylinder of the tank using computational fluid dynamics (CFD) analysis. Miguel et al. evaluated the effect of the filling rate on the gas.