Cold Start Process Research Articles

Proton exchange membrane fuel cell subzero start-up with hydrogen catalytic reaction assistance

The speed of the subzero start-up of proton exchange membrane fuel cells is a hot research topic. However, the cost of the start-up of proton exchange membrane fuel cell is an important factor that affects their commercialization. In this paper, a reused gas cold-start method is developed. Hydrogen–air mixture is introduced to the anode of the fuel cell, and the exhausted gas from the anode is introduced to the cathode. Thermal equilibrium at −20 °C start-up of the fuel cell is calculated. The best gas ratio is confirmed by the start-up process at −20 °C.The fuel consumption and hydrogen utilization of the reused gas cold start and the conventional catalytic reaction cold start are compared. 1/4 is the optimal ration of air/hydrogen. The catalytic reactions take place simultaneously in the anode and the cathode of the fuel cell in there used gas cold-start method, thereby saving energy and time during start up. With this method, the fuel cell can start-up at−40 °C, and the performance of the fuel cell does not seem to change after the cold-start process.

An Experimental Investigation on Low Load Combustion Stability and Cold-Firing Capacity of a Gasoline Compression Ignition Engine

Abstract Gasoline compression ignition (GCI) is one of the most promising combustion concepts to maintain low pollutant emissions and high efficiency. However, low load combustion stability and firing in cold-start operations are two major challenges for GCI combustion. Strategies including negative valve overlap (NVO), advanced injection strategies, fuel reforming, and intake preheating have been proposed in order to solve these difficulties; however, the cold start is still an obstacle. The objective of this work is to study effective methods to achieve GCI engine cold start-up. This work combines NVO, in-cylinder fuel reforming, and intake preheating to achieve quick firing under cold-start conditions and the subsequent warm-up conditions. The results show that start of injection (SOI) during the intake stroke yields the best fuel economy, and injection during the compression stroke has the potential to extend the low load limit. Furthermore, SOI during the NVO period grants the ability to operate under engine conditions with cold intake air and coolant. With highly reactive products made by in-cylinder fuel reforming and fast heat accumulation in the combustion chamber, the NVO injection strategy is highly appropriate for GCI firing. An additional assisted technical method, such as intake preheating, is required to ignite the first firing cycle for a cold-start process. With the combination of NVO, in-cylinder fuel reforming, and intake preheating, the GCI engine successfully started within five combustion cycles in the experiment. After the firing process, the engine could stably operate without further intake preheating; thus, this method is appropriate for engine cold-start and warm-up.

Consistency analysis of polymer electrolyte membrane fuel cell stack during cold start

This paper investigates the cold start characteristic of the polymer electrolyte membrane fuel cell stack in the constant voltage startup mode. The stack is used in actual vehicle working conditions, so it is practical significance to study the cold start characteristics of the stack. The evolution of the temperature and current density distribution at different regions in the constant voltage mode of the stack are studied. Consistency analyzes from two dimensions, in-plane and through-plane are studied. Then, the performance degradation of the stack after the cold start is explored through the polarization curve and the voltage consistency.The cold start characteristics and performance degradation mechanism of the stack are found. The stack has better cold start performance than that of the single cell, which can realize a rapid cold start at −15 °C in 95 s. Also, the performance of the single cell in the middle position is obviously better than that of the single cell on both sides. The internal behavior of each single cell during cold start process is different and the performance consistency is poor after the failed cold start. The performance degradation gradually decreases from the single cell near the inlet to the single cell far away from the inlet. This paper can provide direction for the optimization cold start strategy.

Realizing low emissions on a hydrogen-fueled spark ignition engine at the cold start period under rich combustion through ignition timing control

This paper analyzed low emissions on a hydrogen-fueled spark ignition (SI) engine at the cold start period under rich combustion through ignition timing (IT) control. Cold start characteristics of hydrogen-fueled engine were investigated experimentally. The study was performed under different IT. The results demonstrated that when excess air ratio (λ) was 0.7 and IT varied from 25 °CA BTDC to 10 °CA ATDC, the peak cylinder pressure of the first cycle and the successful start time (SST) of hydrogen engine first increased and then decreased with the retard of IT. At 15 °CA BTDC, the hydrogen engine gained the shortest SST and the highest cylinder pressure in the first cycle. Flame development period (CA0-10) first shortened and then lengthened, and flame propagation period (CA10-90) prolonged when IT gradually retarded. The average NOx emissions efficiently reduced by 90.2%, HC and CO emissions caused by the evaporated lubricant oil reduced individually by 33.8% and 19.7% in the first 6 s during the cold start process with the retard of IT. Especially when IT delayed from 25 °CA BTDC to 15 °CA BTDC, the effect of IT on HC emissions was significant.

Investigation on cold start of polymer electrolyte membrane fuel cells with different cathode serpentine flow fields

The flow velocity and pressure distribution of the three cathode flow fields are simulated in this study. Larger pressure drop and more rapid flow rate reduce residual water, resulting in minimal ice formation during the cold start process. The simulation results show that the single variable cross section serpentine flow field has the largest pressure drop and the most rapid flow rate.The evolution of the temperature and the segment current density characteristics of three different cathode flow fields during cold start process is studied by printed circuit board technology. The results show that the 2 to 1 serpentine flow field has the best cold start performance and the best current density uniformity when cold start at constant voltage mode above −5 °C. However, the single variable cross section serpentine flow field has the best performance when cold start temperature is below −5 °C. Based on these results, cold start at −30 °C can be realized in 97s by using hot antifreeze liquid.

Experimental study on the combustion characteristics of impinging diesel spray at low temperature environment

Impingement is a typical phenomenon occurring in diesel engine under cold start conditions. In this paper, the ignition and combustion characteristics of wall-impinging diesel spray under different wall conditions were investigated by using the high-speed photography, Mie scattering and Schlieren method on a constant volume chamber. It is found that the small wall distance and high wall temperature can accelerate the vaporization and mixing process of the spray, which shorten the ignition delay and accelerate the development of the flame. The wall angle has an obvious influence on the ignition position. The initial flame often appears first in the front of the downward spray. With the increase of wall angle, the promoting effect of the wall to the atomization and ignition is weakened, and the ignition delay increases. It is also found that the promotion of the wall on the combustion process mainly depends on the velocity component perpendicular to the wall. The research results of this paper will provide the basis of the control strategy for the cold start process of diesel engine.

Spray impingement wall film breakup by wave entrainment

Fuel spray impingement on engine wall and piston in the spark-ignition direct-injection (SIDI) setting has been considered a major concern in the aspect of engine emission and combustion efficiency. Excess wall film will result in deterioration of engine friction, incomplete combustion, and substantial cycle-to-cycle variations. These effects are more pronounced during engine cold-start process. Therefore, the formation of wall film on engine wall/piston and the dynamic process of the wall film interacting with impinging spray and spray-induced gas flow are of great significance for reducing wall film mass. However, the dynamic process of wall film was not investigated thoroughly in existing literatures. This work will present a high-speed, simultaneous measurement of a single-hole spray structure, as well as wall film geometry and thickness, via Mie scattering and volumetric laser-induced fluorescence, respectively. Quantitative film thickness measurement was achieved via fluorescence intensity signal calibration with a known, wedge-shape liquid film apparatus. Remarkable wall film droplet entrainment at the leading edge of the liquid film waves was revealed in the measurement, which has not been adequately depicted or analyzed in existing spray impingement studies. A considerable amount of liquid droplets detaches from the liquid film via liquid film fingering, during which process the quantity of liquid mass on the wall is decreased. Quantitative analysis of such phenomenon is performed and we estimated that a liquid mass equivalent to 30–40% of the residual liquid film mass is detached from the liquid film via wave entrainment. Furthermore, through the comparative study of the side view of the spray and the liquid film caused by spray impingement, it is shown that non-uniform spray structure is likely the cause of liquid film wavy motions. These observations suggest that wave entrainment should be considered by numerical models and experimental designs to accurately predict spray impingement phenomenon.

Cold-Start Computational Fluid Dynamics Simulation of Spark-Ignition Direct-Injection Engine

Reliably starting the engine during extremely cold ambient temperatures is one of the largest calibration and emissions challenges in engine development. Although cold-start conditions comprise only a small portion of an engine's typical drive cycle, large amounts of hydrocarbon and particulate emissions are generated during this time, and the calibration of cold-start operation takes several months to complete. During the cold start period, results of previous cycle combustion event strongly influences the subsequent cycle due to variations in engine speed, residual fraction, residual wall film mass, in-cylinder charge and wall temperatures, and air flow distribution between cylinders. Including all these parameters in computational fluid dynamics (CFD) simulation is critical in understanding the cold start process in transient and cumulative manner. Measured cold start data of a production of four-cylinder spark-ignition (SI) direct-injection engine were collected for this study with an ambient temperature of −30 °C. Three-dimensional (3D) transient engine flow, spray, and combustion simulation over first three consecutive engine cycles is carried out to provide a better understanding of the cold-start process. Measured engine speed and one-dimensional (1D) conjugate heat transfer (CHT) model is used to capture realistic in-cylinder flow dynamics and transient wall temperatures for more accurate fuel–air mixing predictions. The CFD predicted cumulative heat release trend for the first three cycles matches the data from measured pressure analysis. The same observation can be made for the vaporized fuel mass as well. These observations are explained in the report.

Numerical investigation of cold-start behavior of polymer electrolyte fuel cells in the presence of super-cooled water

In this study, a mathematical model has been developed to simulate the transient cold-start processes of polymer electrolyte fuel cells. The super-cooled water is assumed to exist within the cell. The non-equilibrium water transfer between the membrane and the catalyst layer is considered. The models of water freezing and ice melting in the catalyst layer and gas diffusion layer have been established. For the first time, the randomicity of the freezing process is captured by introducing a freezing probability function. Based on this model, the cold-start processes of a single polymer electrolyte fuel cell starting at various operating and initial conditions have been simulated numerically. The results indicate that the cold-start performance of the cell is determined by the water storage potential of the electrolyte in cathode catalyst layer. For each startup temperature and operating current load, there is a most appropriate initial membrane water content, which corresponds to the longest cell shutdown time. When the cold-start process is failed, the ice is mainly accumulated in the cathode catalyst layer. The ice distribution becomes more non-uniform as the cold-start temperature is lower.

Optimal Control Strategy for Series Hybrid Electric Vehicles in the Warm-Up Process

To address the problems of low efficiency and high fuel consumption during the cold start and warm-up processes of internal combustion engines, a series hybrid electric vehicle was selected as the research object and two optimal control strategies were designed. A bench test was performed to determine the following: (a) the influence of engine coolant temperature on effective thermal efficiency; and (b) the relationship between engine operating conditions and coolant temperature increase rate. On the basis of the test results, two sets of warm-up process optimization control strategies were designed using a dynamic programming method and a fuzzy control method based on equivalent consumption minimization strategy (ECMS). The test results show that the fuzzy control method for the coolant temperature can effectively shorten the time required to warm up the engine, and the energy consumption of warm-up process can be reduced by nearly 10% through the dynamic programming method.

Additional injection timing effects on first cycle during gasoline engine cold start based on ion current detection system

This paper focuses on the first firing cycle of a cold start process as a means to improve combustion performance and reduce emissions during the cold start of a combined injection strategy engine. A novel additional firing strategy, based on a modified form tandem ion current (IC) signal detection system, was applied to avoid an in-cycle misfire condition. Specifically, by detecting the misfire with the IC signal and then using an additional injection and spark ignition strategy, misfire can be avoided in the current cycle by successful survival combustion. However, if the quantity of additional injection fuel is improper, a misfire may still happen even if this strategy is applied. Furthermore, the requirement for additional fuel was found to be sensitive to the primary ignition timing. Thus, the effects of different ignition timings on the combustion and emissions of the first cycle were also studied. If the additional injection occurs near top dead centre, less fuel needs to be injected to avoid misfire. Having the additional injection timing occur too early or too late were both disadvantageous for additional spark ignition. This is determined by spray condition and piston movement in the cylinder, which is explained in detail by numerical simulation in this paper. Increasing the amount of additional injection fuel can stabilise combustion, but this also increases the hydrocarbon (HC), particulate number (PN), and particulate mass (PM) emissions. If the additional spark ignition fails to cause the combustion after additional injection and ignition, the HC emissions will not dramatically increase compared with basic misfire operation, but the PM will. However, the PM emissions are still at the same level as in normal combustion because the basic misfire condition causes ultra-low PM emissions.

Research on Misfire and Additional Spark Ignition at First Combustion Cycle during Cold Start based on a Modified Form Tandem Ion Current Detection System on a PFI/GDI Engine

This paper focuses on the first firing cycle of a cold start process as a means to improve combustion performance and reduce emissions during the cold start of a combined injection strategy engine. A novel additional firing strategy, based on a modified form tandem ion current (IC) signal detection system, was applied to avoid an in-cycle misfire condition. Specifically, by detecting the misfire with the IC signal and then using an additional injection and spark ignition strategy, misfire can be avoided in the current cycle by successful survival combustion. However, if the quantity of additional injection fuel is improper, a misfire may still happen even if this strategy is applied. Furthermore, the requirement for additional fuel was found to be sensitive to the primary ignition timing. Thus, the effects of different ignition timings on the combustion and emissions of the first cycle were also studied. If the additional injection occurs near top dead centre, less fuel needs to be injected to avoid misfire. Having the additional injection timing occur too early or too late were both disadvantageous for additional spark ignition. Increasing the amount of additional injection fuel can stabilize combustion but this also increases the hydrocarbon (HC), particulate number (PN) and particulate mass (PM) emissions. If the additional spark ignition fails to cause the combustion after additional injection and ignition, the HC emissions will not dramatically increase compared with basic misfire operation, but the PM will. However, the PM emissions are still at the same level as in normal combustion because the basic misfire condition causes ultra-low PM emissions.

Effect of membrane electrode assembly design on the cold start process of proton exchange membrane fuel cells

A transient multiphase model for cold start process is developed considering micro-porous layer (MPL), super-cooled water freezing mechanism and ice formation in cathode channel. The effect of MPL's hydrophobicity on the output performance and ice/water distribution is investigated under various startup temperatures, structural properties, membrane thicknesses and surrounding heat transfer coefficients. Under the maximum power startup mode, it is found that the hydrophobicity disparity of MPL has negligible influences when started from −15 °C, but it strongly affects the overall performance when started from −10 °C, especially after the cell survives the cold start. Decreasing the MPL's hydrophobicity leads to higher current density, meanwhile, it facilitates the super-cooled water's removal, which in turn reduces the ice formation in catalyst layer. However, excessive water accumulation happens if the generated water is hindered from getting into gas diffusion layer (GDL) due to the significant hydrophobicity gap. Weakening the GDL's hydrophobicity contributes to the water removal since the generated water is easier to diffuse out. A thinner membrane benefits the cold start owing to the reduction of ohmic loss and improvement of membrane hydration, and is more sensitive to the hydrophobicity of MPL. Ice formation in cathode channel is identified under various surrounding heat transfer coefficients.

Challenges and opportunities in modelling of proton exchange membrane fuel cells (PEMFC)

Challenges and opportunities in modelling of proton exchange membrane fuel cells (PEMFC)

Investigation of the internal behavior in segmented PEMFCs of different flow fields during cold start process

In this study, we have researched the internal behavior in segmented proton exchange membrane fuel cells (PEMFCs) with three different flow fields during cold start process. The change of internal current density and temperature in fuel cells with different flow fields could be obviously shown by the printed circuit board (PCB) technology, and the study shows that the flow field is significant for enhancing the cold start ability and durability. Single serpentine flow field has the best cold start performance, while triple channel serpentine flow field has the best uniformity. It is found that without a robust temperature rising tendency, the cell temperature reaching 0 °C does not definitely mean a successful cold start because the cell temperature might drop down 0 °C again. Polarization curves show that there is almost no performance degradation after successful cold start, but the cell degrades quickly after the failed cold start at −7 °C and −10 °C. Based on these characteristics, we optimized the rapid cold start strategy by using electric heating and make it possible to start up the PEMFC at temperatures down to −20 °C within about 11 min.

Cold starting characteristics analysis of hydraulic free piston engine

The cold start characteristic of hydraulic free piston diesel engine may affect its stable operation. Therefore the specific cold start characteristics, such as BDC or TDC positions, pressure in-cylinder, heat release rate, should be investigated in detail. These parameters fluctuate in some regularity in the cod start process. With the development of the free piston engine prototype and the establishment of test bench, the results are obtained. For the dynamic results, the fluctuation range of TDC and BDC positions is 8 mm and decreases with time. The thermodynamic results show that the combustion process is not stable and the pressure in-cylinder fluctuates largely in the cold start process. In addition, the combustion is rapid and knock happens inevitably. In order to investigate the reasons, a CFD model is established for temperature analysis in-cylinder and heat transfer conditions. It is found that higher start wall temperature will lead to more uniform temperature distribution. The delay period may decreases and heat release will move forward. This reason is analyzed by thermodynamic derivation based on the first law of thermodynamics. Finally, the improvement suggestions of cold start strategy are proposed.

9-1-1 酸化物触媒の還元・酸化能を利用した酸化的改質の常温駆動プロセスの構築

9-1-1 酸化物触媒の還元・酸化能を利用した酸化的改質の常温駆動プロセスの構築

Study on biodiesel heat transfer through self-temperature limit injector during vehicle cold start

A type of Self-Temperature Limit-Injector (STL- injector) is proposed to reduce the biodiesel consumption and emission in vehicle cold start process. The STL-injector is capable of fast raising fuel temperature, which helps improve the quality of diesel spray and its combustion efficiency. A STL-injector model is established with consideration of electro-mechanic coupling and fluid-structure interaction. A transient simulation is conducted using dynamic grid technology. The results show that STL-injector can effectively raise biodiesel temperature to 350K from 300K in 32 seconds. That is to say, adding STL-injector to existing biodiesel combustion system is an environment-friendly solution due to improving atomization and spray quality quickly.

Elucidating the constant power, current and voltage cold start modes of proton exchange membrane fuel cell

Constant power cold start mode of proton exchange membrane (PEM) fuel cell is essential in practical applications, however, unlike the constant current and voltage cold start modes, the constant power mode was largely ignored in previous fundamental modeling and experimental studies. In this study, a PEM fuel cell stack cold start model for analyzing the constant power cold start process is developed, and the fundamental differences among the various start-up modes are elucidated. In the constant power cold start mode, the start-up process may fail before the ice fully covers the cathode catalyst layers (CLs), because the stack may not be able to supply the required power output, which is different from the constant current and voltage start-up modes. The initial water content and start-up temperature could limit the power output significantly. The constant power can be controlled at higher current (CPHC) or lower current (CPLC). In the CPHC mode, the current density decreases and the stack voltage increases during the cold start process, while it is reversed in the CPLC mode. Generally, the CPLC mode produces less heat during cold start process than the other start-up modes, because the current density is often kept at low level.

Experimental investigation on dynamic characteristics of proton exchange membrane fuel cells at subzero temperatures

Cold start and operation of a proton exchange membrane fuel cell (PEMFC) at the cold temperatures are crucial to the commercialization of it in the field of transportation. A 32 cm 2 two cell stack is prepared to conduct the experiments at subzero temperatures, including cold start processes and cell performance testing, aiming of the characteristics of the cell. The startup study under subfreezing temperatures is conducted by galvanostatic method at various operation conditions, i.e. ambient temperature (−3 and −5 °C), current density and anode stoichiometry. The results show that the voltage evolutions are proportional to the operating current densities under the former two conditions, but the relationship becomes the opposite at the last condition. It is also found that the time constant for the cell to reach steady status is no more than 100 s and highly depends on the startup mode. In addition, the performance of the cell is tested at the temperature of 0 °C and −3 °C. The comparison of pre-humidification and normal operations indicate that the initial water content of membrane affects the cell performance. • The voltage response is proportional to ambient temperature and current density. • There exists a time constant for the response to be stable. • The initial membrane water content is beneficial to the cell performance.