Refine Your Search

Topic

Search Results

Technical Paper

Numerical Simulation of Surface Temperature Fluctuation and Thermal Barrier Coating at the Piston Top for a Diesel Engine Performance Improvement

2021-04-06
2021-01-0229
Low heat rejection (LHR) combustion has been recognized as a potential technology for further fuel economy improvement. This paper aims to simulate how the piston top’s thermal barrier coating affects the engine’s thermal efficiency and emissions. Accordingly, a Thin-wall heat transfer model in AVL Fire software was employed. The effects of increasing the piston top surface temperature, comparing different thermal barrier coating material, were simulated at the engine’s rated power operating point, so as the piston top’s surface roughness. In comparison to a standard diesel engine, the indicated thermal efficiency (ITE) could increase by 0.4% when the surface temperature of the piston top changed from 575K to 775K.
Technical Paper

Anode Pressure Control with Fuzzy Compensator in PEMFC System

2021-04-06
2021-01-0121
Hydrogen safety is of great importance in proton exchange membrane fuel cell (PEMFC) systems. Anode pressure control has become a focus point in recent years. The differential pressure between anode and cathode in PEMFC system needs to be carefully controlled under a suitable threshold. In practice, the anode pressure is usually controlled about 20–30kPa higher than the cathode pressure to minimize nitrogen crossover and improve cell stability. High differential pressure could lead to irreversible damage in proton exchange membrane. PID control was the dominant method to control the anode pressure in the past. However, the anode pressure’s fluctuation when hydrogen mass flow suddenly changes is a long-term challenge. As the requirements of control precision are increasingly high, the traditional PID control needs to be improved. Several new control algorithms are presented in recent researches, however, mostly are theoretical and experimental.
Technical Paper

Optimal Gearshift Strategy in Inertia Phase of Dual-Clutch Transmissions

2021-04-06
2021-01-0320
Shift quality is an important indicator to measure the performance of dual-clutch transmissions (DCT). To obtain optimal driving comfort and reduce the vehicle jerk as much as possible, this paper proposes an integrated gearshift controller to control the engine and the on-coming clutch in inertia phase. First of all, a dynamic model of DCT during gearshift is established. Key factors determining shift quality are analyzed. In order to reduce the vehicle jerk, a reference trajectory of the engine speed and the derivative of the desired torque transferred by the on-coming clutch in inertia phase are programmed respectively. A back-stepping sliding mode controller (BPSMC) is designed to make the actual engine speed track the reference trajectory and an incremental proportional-integrative (PI) controller is designed to make the actual clutch torque to track the desired clutch torque.
Technical Paper

Effect of Injection Parameters on Particulate Matter Emission in a Direct Injection Gasoline Engine

2021-04-06
2021-01-0628
PN(Particle Number) emission limits are more stringent for gasoline vehicles in Chinese VI emission standards (6×1011 #/km). A EEPS engine exhaust particle size spectrometer was employed to characterize the effects of injection strategies on particulates emissions from a turbocharged gasoline direct injection (GDI) engine. The effects of operating parameters (injection pressure, second injection ratio and second injection end time) on particle diameter distribution and particle number density of emission was Investigated. The experimental result indicates that the quantity of particles decrease with the increase of injection pressure obviously, especially at high load including the 20% reduction of the particle number density. When the engine is at low load, the accumulation mode particle emissions are higher than the nucleation mode particle emissions compared with high load, which present opposite results. The second injection can restrain engine knock at low speed.
Technical Paper

A Comparative Study of Fuel Cell Prediction Models Based on Relevance Vector Machines with Different Kernel Functions

2021-04-06
2021-01-0728
Fuel cell reactors, as the core components of fuel cell vehicles, have a short life problem that has always limited the development of fuel cell vehicles. The life attenuation curve of fuel cell shows nonlinear characteristics, and there is no model that can accurately predict its effect. This paper is based on the experimental data of the vehicle fuel cell reactor, which is derived from the 600 h durability test run by a 4 kW fuel cell reactor. The relevance vector machine, as a Bayes processing method that supports vector machine, is a data-driven method based on kernel functions. The regression model is established by the relevance vector machine, and the super-parameters are found by genetic algorithm, because the kernel function strongly affects the nonlinearity of the curve, and the decay curve of fuel cell reactor performance is predicted according to four different kernel functions.
Technical Paper

Design and Structural Parameters Analysis of the Turbine Rotor in Fuel Cell Vehicle

2021-04-06
2021-01-0729
As the most power-consuming component of the fuel cell system, the compressor directly affects the efficiency of the system. Using turbines to recover energy from the exhaust gas, has become a feasible means to improve the fuel cell system’s efficiency. Previous designs are mainly based on high-temperature (>523.15 K) gas. However, the exhaust gas temperature of the proton exchange membrane fuel cell is only about 348.15 K, which is much lower than the working fluid temperature of typical turbines (such as those used in internal combustion engine). In this paper, a turbine rotor for a 100kW fuel cell system was designed. The influences of non-design structural parameters including blade inlet incline angle, blade thickness, blade tip clearance and blade number on the aerodynamic performance and internal flow of the rotor are investigated. Computational fluid dynamic (CFD) model of the rotor single flow is established to predict the turbine aerodynamic performance.
Technical Paper

Experimental Investigation of Control Strategies on Voltage Inconsistency for Proton Exchange Membrane Fuel Cells

2021-04-06
2021-01-0736
Proton exchange membrane fuel cells (PEMFC) is considered the most promising alternative vehicle power in the future owing to its highly power density and zero carbon emission. However, Voltage inconsistency of PEMFC is an essential issue that influences the performance of a PEMFC. It is affected by flow-rate and relative humidity of the inlet air. It’s necessary to establish a control strategy to ensure air supplied timely. A PEMFC system bench with 30 cells (the cells are numbered 1-30 in the direction from near to far from the air intake port) assembled in series was established to investigate the control strategy of air supply system. According to fuel cell’s position of the lowest voltage and the corresponding air flow rate, there are three different operations as follows. When it appears not in the low numbered area and the air flow rate is high, it indicates that humidity of the cell is insufficient and it needs to reduce power of the blower or close the bypass-valve.
Technical Paper

Investigating the Effect of Water and Oxygen Distributions on Consistency of Current Density Using a Quasi-Three-Dimensional Model of a PEM Fuel Cell

2021-04-06
2021-01-0737
Activation loss, mass transfer loss and ohmic loss are the three main voltage losses of the polymer electrolyte membrane fuel cell. While the former two types are relevant to concentration of oxygen in catalyst layer and the later one is associated with the water content in membrane. Distributions of water content and oxygen in a single cell are inconsistent which cause that current densities in each segment of the single cell are different. For the dry inlet gas, the water in the segments near the gas inlet channel will be carried to the segments near the gas outlet channel, which causes high ohmic loss of the segments near the gas inlet channel. In this work, a transfer non-isothermal quasi-three-dimensional model is developed to investigate inconsistency of current densities.
Technical Paper

Investigation on Cold Start for Proton Exchange Membrane Fuel Cell Stack

2021-04-06
2021-01-0738
Cold start remains a major obstacle to the commercialization of proton exchange membrane fuel cell (PEMFC), however, there are few studies on the cold start characteristics, especially at a complicated stack level. In this study, a novel layer-lumped numerical model with higher computational efficiency is proposed to investigate the cold start behavior of PEMFC stack, in which phase transition, heat transfer and electrochemical reaction are comprehensively considered. Besides, phase transition mechanisms are reconstructed based on the assumption that super-cooled water exists within the cell. With this model, the inconsistency of the stack temperature distribution and output performance is presented, some constant loading voltage strategies are investigated, and a linear variable controlling voltage strategy is developed.
Technical Paper

Optimization of Speed Fluctuation of Internal Combustion Engine Range Extender by a Dual Closed-Loop Control Strategy

2021-04-06
2021-01-0782
With the increasing concern on environmental pollution and CO2 emission all over the world, range-extended electrical vehicle (REEV) has gradually got more attention because it could avoid the mileage anxiety of the battery electrical vehicles (BEV) and get high energy efficiency. Nevertheless, NVH performance of internal combustion engine range extender (ICRE) is a critical problem that affects the driving experiences for REEV. In this paper, a two-cylinder PFI gasoline engine and a permanent magnet synchronous motor (PMSM) are coaxially mounted to run as an ICRE. The ICRE control system was established based on Compact RIO hardware and LabVIEW, who has the functions of the intake throttle PID closed-loop control, autonomous ICRE operation control, and speed PID closed-loop control. In this paper, the gasoline engine was first driven to the idle condition by PMSM in speed-control mode.
Technical Paper

The Control Strategy for 4WD Hybrid Vehicle Based on Wavelet Transform

2021-04-06
2021-01-0785
In this paper, in order to avoid the frequent switching of engine operating points and improve the fuel economy during driving, this paper proposes a control strategy for the 4-wheel drive (4WD) hybrid vehicle based on wavelet transform. First of all, the system configuration and the original control strategy of the 4WD hybrid vehicle were introduced and analyzed, which summarized the shortcomings of this control strategy. Then, based on the analyze of the original control strategy, the wavelet transform was used to overcome its weaknesses. By taking advantage over the superiority of the wavelet transform method in multi signal disposition, the demand power of vehicle was decomposed into the stable drive power and the instantaneous response power, which were distributed to engine and electric motor respectively. This process was carried out under different driving modes.
Technical Paper

Numerical Study on Flammability Limit and Performance of Compression-Ignition Argon Power Cycle Engine with Fuel of Hydrogen

2021-04-06
2021-01-0391
The argon power cycle engine, which uses hydrogen as fuel, oxygen as oxidant, and argon other than nitrogen as the working fluid, is considered as a novel concept of zero-emission and high-efficiency system. Due to the extremely high in-cylinder temperature caused by the lower specific heat capacity of argon, the compression ratio of spark-ignition argon power cycle engine is limited by preignition or super-knock. Compression-ignition with direct-injection is one of the potential methods to overcome this challenge. Therefore, a detailed flammability limit of H2 under Ar-O2 atmosphere is essential for better understanding of stable autoignition in compression-ignition argon power cycle engines.
Technical Paper

Study on the Constant Voltage, Current and Current Ramping Cold Start Modes of Proton Exchange Membrane Fuel Cell

2021-04-06
2021-01-0746
The cold-start of proton exchange membrane fuel cell (PEMFC) has been one of the technical challenges for fuel cell vehicle table ommercialization. In this study, a one-dimensional cold start transient model of PEMFC was developed for the transfer of water, heat, electrons and protons during the cold start process. Different loading modes, including constant voltage, constant current, and current ramping, were adopted for fuel cell cold starting analysis, respectively. The internal water-heat transfer within fuel cell was investigated under different loading modes. The results show that in the constant current mode, for the high current, the cold start process can produce more heat than other modes, which can increase fuel cell temperature rapidly. However, this process may easily fail before the ice fully covers the cathode catalyst layers (CL).
Technical Paper

Control Strategies for Prevention of PEMFC Oxygen Starvation: A Review

2021-04-06
2021-01-0743
Proton Exchange Membrane Fuel Cell (PEMFC) which has advantages of starting fast, high energy density, high efficiency, lower operating temperature and little pollution is widely regarded as one of the most promising energy sources. The PEMFC system includes several subsystems such as air supply subsystem, hydrogen supply subsystem, thermal management subsystem, water management subsystem, energy management subsystem and so on. The Air supply subsystem has great influence on the performance and life of PEMFC stack. Whether oxygen supply in air supply subsystem is sufficient or not will affects reaction rate of fuel, the operating temperature and degradation of PEMFC stack and so on. To solve the issue of oxygen starvation in PEMFC stack, the control strategies for improving dynamic response and preventing air shortage of the PEMFC air supply subsystem are reviewed.
Journal Article

A Data Driven Fuel Cell Life-Prediction Model for a Fuel Cell Electric City Bus

2021-04-06
2021-01-0739
Life prediction is a major focus for a commercial fuel cell stack, especially applied in fuel cell electric vehicles (FCEV). This paper proposes a data driven fuel cell lifetime prediction model using particle swarm optimized back-propagation neural network (PSO-BPNN). For the prediction model PSO-BP, PSO algorithm is used to determine the optimal hyper parameters of BP neural network. In this paper, total voltage of fuel cell stack is employed to represent the health index of fuel cell. Then the proposed prediction model is validated by the aging data from PEMFC stack in FCEV at the actual road condition. The experimental results indicate that PSO-BP model can predict the voltage degradation of PEMFC stack at actual road condition precisely and has a higher prediction accuracy than BP model.
Journal Article

Aerodynamic Performance Modeling of the Centrifugal Compressor and Stability Analysis of the Compression System for Fuel Cell Vehicles

2021-04-06
2021-01-0733
The centrifugal compressor is one of the most commonly used air compressors for fuel cell air supply systems, and it has the small volume, high pressure ratio and low noise. However, surge in a centrifugal compressor severely limits its stable flow range. In this paper, a mathematical model of the compressor aerodynamic performance based on the energy transfer method was established, some parameters of model were identified by experimental data, and the model was validated through experiments. Then the dynamic model of the compression system was derived based on the compressor model and the Moore-Greitzer model. The stability analysis of the compression system was conducted, and it was strictly proved that when the compression system is unstable, there is the limit cycle in this nonlinear system, namely the surge cycle. Furthermore, the simulation of the compression system was conducted and the instability condition of the compression system was presented.
Journal Article

Review on State of Health Definition in Relation to Proton Exchange Membrane Fuel Cells in Fuel Cell Electric Vehicles

2021-04-06
2021-01-0735
Owing to its advantages of high energy density, quick start-up, and no emissions, the proton exchange membrane fuel cell (PEMFC) is one of the most promising power sources in transportation and has been used for automotive application for years. However, shortcomings in fuel cell key performances, such as lifetime and efficiency, characterized by state of health (SOH), restrict the large-scale commercialization for fuel cell electric vehicles (FCEV), raising demands for real-time state monitoring. Nowadays, most researchers have explored the reasons for state change from models or experiments. Nevertheless, it is in need of system-level researches on definition methods of SOH against the actual automotive application. Lacking accurate quantitative indicators, existing studies on health states are often qualitative and hence fail to consider intermediate processes.
Technical Paper

Multi-target Tracking Algorithm with Adaptive Motion Model for Autonomous Urban Driving

2020-12-29
2020-01-5167
Since situational awareness is crucial for autonomous driving in urban environments, multi-target tracking has become an increasingly popular research topic during the last several years. For autonomous driving in urban environments, cars and pedestrians are the two main types of obstacles, and their motion characteristics are not the same. While in the current related multi-target tracking research, the same motion model (such as Constant Velocity model [CV]) or motion model set (such as CV combined with Constant Acceleration model [CA]) is mostly used to track different types of obstacles simultaneously. Besides, in current research, regular motion models are mostly adopted to track pedestrians, such as CV, CA, and so on, the uncertainty in pedestrian motion is not well considered.
Technical Paper

Decision-Making for Intelligent Vehicle Considering Uncertainty of Road Adhesion Coefficient Estimation: Autonomous Emergency Braking Case

2020-10-29
2020-01-5109
Since data processing methods could not completely eliminate the uncertainty of signals, it is a key issue for stable and robust decision-making for uncertainty tolerance of intelligent vehicles. In this paper, a decision-making for an Autonomous Emergency Braking (AEB) case considering the uncertainty of road adhesion coefficient estimation (RACE) is proposed. Firstly, the 3σ criterion is employed to classify the confidence in order to establish the decision-making mechanism considering the signal uncertainty of RACE. Secondly, the model for AEB with the uncertainty of the road adhesion coefficient estimated is designed based on the Seungwuk Moon model. Thirdly, a CCRs and CCRm scenario was designed to verify the feasibility in reference to the European New Car Assessment Programme (Euro NCAP) standard. Finally, the results of 10,000 cycles test illustrate that the proposed method is stable and could significantly improve the safety confidence both in the CCRs and CCRm scenarios.
Journal Article

Online Estimation of Membrane Water Content in Vehicular PEMFC by Complex Morlet Wavelet Transformations

2020-09-15
2020-01-2255
The amount of water content in membrane electrode assembly (MEA) is an important factor affecting the efficiency and life of proton exchange membrane fuel cell (PEMFC), and there are several methods to measure it. However, it’s widely believed that the most feasible method to measure the water content in the MEA is an indirect way as described below: measure the electrochemical impedance spectroscopy (EIS), and take advantage of the positive correlation between the proton’s conductivity, which is reciprocal of specific resistance, and the water content in MEA. The traditional EIS measurement method has the shortcoming of high cost and slow speed, especially in low frequency bands, so this method is unsuitable for high-power vehicle fuel cell systems. In this paper, a measuring method which does not require a large number of experiments and only need to perform Morlet wavelet transform on the PEMFC voltage signal as well as current signal is proposed.
X