New thermal management system for fuel cell vehicles

01

Background

Electric vehicles (EVs), including battery electric vehicles (BEVs) and fuel cell vehicles (FCVs), are considered promising solutions for achieving zero carbon emissions and new energy utilization in automotive applications. Despite the continued rapid development of BEV technology and marketization, there is a strong impetus for the technological development of FCVs, mainly because they are superior to BEVs in terms of driving distance and charging time; among the many types of fuel cells (FCs), proton exchange membrane (PEM) fuel cells (PEMFCs) are favored mainly because of their low operating temperature (about 80 °C), which allows the vehicle to start quickly.

While generating electricity, PEMFC generates almost the same amount of heat, which needs to be released from PEMFC, otherwise thermal runaway may occur. Appropriate temperature increase will improve the kinetics of the electrochemical reaction, but overheating will not only dehydrate the membrane and reduce proton conductivity, but also greatly aggravate the degradation of the membrane and catalyst, causing irreversible performance loss and damage to PEMFC. Considering the electrochemical reaction, water balance and gas transport, the suitable operating temperature range of PEMFC is between 60 °C and 80 °C. Therefore, the thermal management system (TMS) is crucial for the normal operation of the FCV fuel cell stack (FCS); in addition, the auxiliary power battery, electric motor, electronic components, cabin air and compressed air supplied to the PEMFC all require suitable cooling and heating circuits. Designing an integrated thermal management system (ITMS) for fuel cell vehicles is an important issue.

Unlike pure electric vehicles and internal combustion engine (ICE) vehicles (ICEVs), fuel cell vehicles face more severe challenges in ITMS layout. Since the efficiency of lithium-ion batteries is higher than that of PEMFCs, BEVs release much less heat than FCVs. Compared with BEVs and FCVs, ICEVs generate the most heat; however, a large amount of heat is carried away by the ICE exhaust, while for FCVs, most of the heat removal should be handled by the PEMFC coolant loop because the heat transferred by the exhaust and water is negligible. In addition, the available temperature difference between the radiator and the ambient air of PEMFC is much lower than that of ICE because PEMFC operates at a much lower temperature. Therefore, FCVs require radiators with larger surface areas to remove the same amount of heat as ICEVs. These requirements increase the difficulty of thermal management design for fuel cell vehicles.

02

Achievements

Recently, Jiang Fangming's team from the Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, proposed a new thermal management system using a thermal peak regulator.

The thermal peak regulator is a heat storage device filled with phase change material, which exchanges heat with the fuel cell coolant and air conditioning refrigerant, respectively. It temporarily receives excess heat that cannot be released by the radiator when the thermal peak occurs; later, when the thermal peak disappears, the heat will be transferred to the refrigerant to take it away from the condenser. System simulation based on the developed thermal model shows that this new thermal management system can eliminate or effectively weaken the thermal runaway of the fuel cell stack, depending on the amount of phase change material filled in the thermal peak regulator. In this study, the thermal runaway duration of 135 seconds and 250 seconds can be shortened to 0 seconds and 105 seconds, respectively, in the standardized New European Driving Cycle and the Global Harmonized Light Duty Test Cycle in 38 °C summer weather, and the maximum temperature of the latter can be reduced from 89 °C to 83 °C. This work can make a significant contribution to solving the thermal management problem of fuel cell vehicles.

The research results were published in the Journal of Cleaner Production under the title “A novel thermal management system with a heat-peak regulator for fuel cell vehicles”.

03

Picture and text guide

Figure 1 A novel thermal peak regulator integrated thermal management system for fuel cell vehicles.

Figure 2 Schematic diagram of the “time-varying” thermal management approach and HPR function.

Figure 3 Series arrangement of the front heat exchangers and the thermal interference between them.

Figure 4 Voltage output (Vcell) and power density (Pcell = Vcelli) of a single cell as a function of current density (i).

Fig. 5 Instantaneous vehicle speed (u) and motor power (PM) in (a) NEDC and (b) WLTC driving cycles.

Fig. 6 Instantaneous power output distribution between FCS (PFCS) and LIB (PLIB) based on vehicle motion power (PM) during (a) NEDC and (b) WLTC driving cycles.

Fig. 7 Instantaneous cabin heat load (Qcab) during (a) NEDC and (b) WLTC driving cycles.

Fig. 8 Temporal variation of FCS and cabin air temperature with and without HPR in (a) NEDC and (b) WLTC drive cycles at Tamb = 38 °C. Also plotted are FCS heating (QFCS), cabin heat load (Qcab), and PCU heating (QPCU) superimposed on vehicle speed (u).