Li Jianqiu

Tsinghua University | TH · School of Vehicle and Mobility

The adaptability of fuel cell vehicles in low-temperature environments remains challenging for their commercialization owing to the propensity of water within the fuel cell to freeze during a cold start, which impedes gas transmission and subsequent reactions. Consequently, the initial water content before cold start and the heat and water generate...

The objective of this study is to investigate the potential reduction of polarization in proton exchange membrane fuel cells (PEMFCs) through the design optimization of flow channel. The impact of structural parameters and surface properties of the bipolar plate flow channels on the PEMFC performance is thoroughly examined on a commercial scale PEM...

A promising direction for high-power fuel cell engines is the ejector-based hydrogen recirculation system. As a first step, a hybrid hydrogen recirculation system configuration, consisting of a passive single ejector and a bypass injector, has been proposed. For the system matching design, both a three-dimensional numerical model of the ejector usi...

Increasing the power density of proton exchange membrane fuel cells (PEMFCs) is essential for their commercialization. Cathode catalyst layer (CCL) carbon additive is an effective method that can improve membrane electrode assembly (MEA) performance under high current density. Here, carbon nanofiber (CNF) is used as a CCL additive and its mechanism...

Fuel cells are ideal power sources for aircraft. However, fuel cells are highly sensitive to operating pressure, which complicates the operating characteristics of fuel cells at various altitudes. A globally optimal cathode pressure control method of aircraft fuel cell powertrain system is proposed to address the abovementioned problem. Simplified...

Variable inter-vehicle distances influence significantly the wind resistance of platoon vehicles due to the sheltering of airflow. Accurate air drag estimation is extremely important for platoons in scenarios like energy-oriented driving and high-precision tracking. Most aerodynamic researchers have performed qualitative analysis of wind resistance...

The independently controlled electric wheels of distributed drive vehicles provide faster and more accurate actuators for vehicle slip ratio control. Meanwhile, the estimation of the slip ratio of electric wheels has been of vital importance for the dynamics control of distributed drive electric vehicles. However, the conventional slip ratio estima...

To realize the high-power density of the proton exchange membrane fuel cell (PEMFC), it is important to explain the influence of liquid water on cell voltage quantitatively, which is still not fully understood yet. This paper proposes a study on polarization decomposing of PEMFC considering effect of liquid water accumulation. The voltage model sta...

Polymer electrolyte membrane fuel cell (PEMFC) is a potential candidate as power source for electrified transportation. Technically speaking, PEMFC is an energy conversion device involving complicated physico-chemical processes and its highly non-linear characteristic is very likely to cause unpredictability and non-repeatability, causing confusion...

A simplified one-dimensional proton exchange membrane fuel cell (PEMFC) model is developed to characterize the two-phase flow effect with dimensionless numbers. A new Damköhler number is defined to decouple the gas and liquid flow in electrodes. The flow pattern in gas channels can be predicted by force balance analysis with Reynolds number and Web...

The isopotential assumption of bipolar plate was widely employed to study the heterogeneity within a fuel cell stack, not only for numerical modelling purposes, but also for the deployment of cell voltage monitors (CVMs). Although this assumption is questionable according to previous studies, few comprehensive investigations have been conducted on...

In view of the problem of insufficient flexibly regulating resources the new-type of electricity system faced due to high proportional penetration of renewable energy，a transportation-energy-electricity integrated technology scheme with the new energy vehicle as its core is proposed，coupling energy storage，hydrogen energy and intelligence，with the...

Reducing the channel/rib width is a possible approach to improve the performance of fuel cells. However, few experiments were conducted to verify this claim, especially for channel/rib width of below 0.4 mm. In this study, we conducted quantitative analysis to investigate the influence of channel/rib geometries on the performance of fuel cells thro...

The durability issue of polymer electrolyte membrane fuel cells must be resolved before their widespread commercialization in transportation. A central issue in fuel cell durability is the loss of Pt electrochemical active surface area (ECSA) during automotive conditions, which is induced primarily by the Pt mass loss and Pt particle growth mechani...

The utilization of multiple independently controlled electric wheels offers possibilities for enhancing not only the vehicle stability control but also energy efficiency of a vehicle. Previous research on energy-efficient torque allocation mainly focuses on four-wheel-independent-drive vehicles but not multi-axle all-wheel-drive vehicles. In this p...

Electrification of heavy duty vehicles (HDVs) is critical to realization of the target of carbon neutralization in the future. For most HDVs, the influence of road slope on vehicle power usually cannot be ignored due to significant road slope variation during long driving mileages. In order to design the powertrain system for electrified HDVs effec...

High frequency resistance (HFR) has become the most important input signal for the on-board water management of polymer electrolyte membrane fuel cell (PEMFC) vehicles in practical applications, due to its close physical relation to the membrane water content. However, according to our latest experimental result, the paradox arises that HFR reaches...

For fuel cell research, fuel economy evaluation methods for fuel cell systems are the basic tools; however, current fuel economy evaluation methods do not meet the demand for comprehensive analyses of the economy of fuel cell systems. In this study, we propose an all-condition economy evaluation method for fuel cell systems. To estimate the all-con...

The existing models of proton-exchange membrane fuel cells, such as computational fluid dynamics and lumped-parameter models, cannot provide a comprehensive description of mass-transport mechanisms without incurring a high computational load. This paper proposes a reduced-dimension dynamic model of fuel cells that considers main mass-transport mech...

Electrochemical impedance spectroscopy (EIS) is an important diagnostic tool for fuel cells. Accurate extraction of physical parameters from impedance spectra remains a significant challenge for vehicle fuel cells. The reliability analysis results obtained herein revealed that precise identification of middle and low‐frequency impedance by a tradit...

The transient water transport problem within polymer electrolyte membrane fuel cell (PEMFC) makes its dynamic behavior unpredictable occasionally, bringing uncertainties to the water management. In this work, a novel experimental methodology is proposed, where the dynamic processes of gas diffusion layer (GDL) imbibition-drainage are accomplished b...

The degradation rate of fuel cell performance changes from linear to nonlinear, which plays a role in the poor durability of fuel cells. Little research has been reported on the mechanism and diagnostic methods for the accelerated degradation of commercial fuel cells. An early warning method of fuel cell accelerated degradation based on the high-po...

The continuous chemical degradation of the polymer membrane in polymer electrolyte fuel cells causes membrane pinhole formation, therefore substantial increase in the gas cross-over flux. In this paper, a numerical method to simulate the pinhole formation process during chemical degradation is proposed. The method assumes that a membrane pinhole is...

In order to enhance the power and bring additional energy-saving possibilities of heavy-duty vehicles, a novel dual-engine system is utilized in a series hybrid electric vehicle. However, the minimum fuel consumption of this configuration is still unclear, and the effective online energy management strategy for this system is absent. The studied ve...

The nonlinear, accelerated decline of fuel cells is a major cause of diminished service life, which is difficult to be detected in early warning. Through in situ electrochemical diagnosis, we found that the accelerated decline of fuel cell could not be directly predicted by the crossover current or the electrochemically active surface area. Surface...

Low temperature charging is a major challenge for lithium-ion batteries, since it could lead to dramatic performance degradation and potential safety issues. A pre-heating process is usually applied to overcome above-mentioned challenges. Pulsed operation is adopted as one of established internal pre-heating methods with good temperature uniformity...

Water flooding occurs at the output region of the anode side, which is one of the main reasons for performance degradation of automotive fuel cell systems. If liquid water saturation ratio in gas diffusion layers can be observed and regulated within a suitable range, water flooding in anode channels can be avoided. For this purpose, a zero dimensio...

The rotor position is a key state in the closed-loop control system of the permanent magnet synchronous motor (PMSM). Its measurement accuracy has a significant effect on steady accuracy, dynamic response, and torque ripple. The magnetoresistance (MR) sensor is widely used in the rotor position detection due to its distinct advantages, such as simp...

Sub-zero startup ability remains a key barrier for commercial application of polymer electrolyte fuel cells (PEMFC), especially for automotive applications. In order to improve the startup ability and durability of fuel cells, understanding of the characteristics and mechanisms of cold start is essential, and here modeling of fuel cell cold start p...

Self-humidification with anode/cathode recirculation was found to be an alternative in the place of external humidifier according to the previous studies in the last decade, however, there is still a lack of quantitative experimental and theoretical comparison between them. In this study, the dynamic PEM fuel cell system model with anodic and catho...

Lithium-ion (Li-ion) cells degrade after repeated cycling and the cell capacity fades while its resistance increases. Degradation of Li-ion cells is caused by a variety of physical and chemical mechanisms and it is strongly influenced by factors including the electrode materials used, the working conditions and the battery temperature. At present,...

Battery electric vehicles with a range of more than 500 km are expected to become increasingly competitive in the future. The energy density of the currently available lithium batteries should be significantly increased to support the operation of such vehicles, and high-power charging is required to reduce the charging time. However, high-power ch...

In this paper, a general torque distribution strategy is proposed to improve the drivetrain efficiency of four-wheel-drive electric vehicles (EVs). The strategy allows the same or different motors to be equipped in the front and rear wheels. The model of the drivetrain considers the loss properties of four permanent magnet synchronous motors (PMSMs...

High-power charging (HPC) has been associated with a great potential to shorten the charging time, relative to increasing the all-electric range (AER) of battery electric cars (BECs). Such promise of applicability is however restrained by setbacks attributed to the high-voltage system of BECs, its negative influence on the battery performance, and...

The lithium ion battery is widely used in electric vehicles (EV). The battery degradation is the key scientific problem in battery research. The battery aging limits its energy storage and power output capability, as well as the performance of the EV including the cost and life span. Therefore, a comprehensive review on the key issues of the batter...

The hysteresis of PEM fuel cell output voltage of the single cell and multi-cell stack is presented by experiments, during which the in-situ liquid water visualization at certain point of gas channel, quantitative measurement of the RH (relative humidity) and HFR (high frequency resistance) by EIS (electrochemical impedance spectroscopy) were carri...

Battery electric buses (BEBs) play a very important role of reducing urban tailpipe emissions in transportation sector for China. The national strong incentive policies place China at the forefront of the BEBs’ market in the world. However, challenges are even more severe owing to the negative effects of national subsidies on the BEBs industry and...

A suitable model structure and matched model parameters are prerequisites for the precise estimation of the battery states. Previous studies pay little attention to whether a parameter identification method is suitable for a model. In this study, a comparative study is conducted by implementing model parameter optimization for nine equivalent circu...

A 2D PEMFC model has been built to simulate the current density distribution and liquid water distribution in cathode. In this simulation, the air mass flow rate, relative humidity of the air and cell voltage are considered as the input parameters into the model, the diagram of current density and liquid water distribution in cathode are shown acco...