Pumping Losses Research Articles

Experimental investigation of the effects of CR, hydrogen addition strategies on performance, energy and exergy characteristics of a heavy-duty NGSI engine fueled with 99% methane content

In order to analyze and improve thermodynamic process of NGSI engine and achieve better energy utilization, a low CR (11.6) SI engine was modified by replacing pistons with different bowl volumes and an experimental investigation of the effects of CR (13.6 and 14.5), hydrogen addition strategies on performance, energy and exergy characteristics of a heavy-duty NGSI engine fueled with 99% methane content was conducted. The results showed that the PCP, maximum HRR and in-cylinder temperature increased obviously with the increase of hydrogen contents, CR and engine speed, and the locations of PCP and maximum HRR advanced towards TDC, which led to the advance of 50% combustion position, shorter combustion duration and more output work. Secondly, with the increase of hydrogen contents and CR, the proportions of indicated work and heat transfer energy to coolant turned larger but the unaccounted losses and combustion loss became smaller. In addition, with the increase of engine speed, both indicated work and friction loss were large, which caused the decrease of BTE, besides, the percentage of friction loss and pumping loss turned up. And the hydrogen contents and CR had little effect on exhaust energy and exergy. Finally, comparing the energy and exergy of NGSI engine under operated conditions, the change trends of exergy terms were similar to their corresponding energy, however, the exergy efficiency was 7.97–9.70% lower than BTE and the percentage of exhaust energy and heat transfer energy to coolant was 2.46–2.51 and 7.09–8.09 times larger than corresponding energy, respectively.

Electrolyte Flow in Vanadium Redox Flow Batteries

The redox reactions inside a Vanadium Redox Flow Battery (VRFB) are catalyzed by a porous carbon felt electrode, through which the vanadium containing electrolyte is pumped. Thus, a high Electrochemically Active Surface Area (ECSA), corresponding to a high saturation of the porous electrode, is beneficial to the performance. Maintaining a low mass transport resistance inside the flow felt is important to reduce parasitic pumping losses, which decrease the overall efficiency of the battery system. The pressure drop was measured, as it is directly related to the pumping losses caused by the flow through the pores. X-ray tomography and X-ray radiography were used to visualize the distribution of the electrolyte inside the pores. The effect of thermal activation (400 °C, 25 h) and compression of the carbon electrode on the wetting behavior of the electrolyte was investigated, as it correlates with the ECSA and the oxygen content on the electrode surface1. Furthermore, the changes in flow behavior of the redox active vanadium species with a different oxidation number are of interest, as it could imply separate optimization parameters for the anode side and the cathode side. The redox-active vanadium species in the electrolyte exist in four different states, V(II), V(III), V(IV), and V(V). In this work, the X-ray based techniques were used in an ex situ injection setup2. VRFB electrolytes (V(IV), V(V), V(II), V(III), all 0.1 M in 2M H2SO4) were injected into a commercially available porous carbon felt electrode ((GFA 6EA) from SIGRACELL® battery electrodes (SGL Carbon, Germany)) under controlled degrees of compression (20%, 50%, 70% of the uncompressed height). After an initial imbibition of the electrode, which was stopped immediately after the electrode wicked the electrolyte, a higher flow-rate was applied to simulate operating conditions. Synchrotron X-ray radiography shows the invasion and progression of the liquid electrolyte into the pores and indicates that capillary forces are initially dominant, but numerical simulation of the flow-through suggests that other forces come into play as well at higher flow velocities3. The study shows that the thermal activation plays the major role in the wetting behavior, increasing the saturation inside the electrode by more than 200% and decreasing the pressure drop by a factor of two when the electrolyte is injected into a thermally activated electrode, in agreement with Banerjee et al.3. The influence of the vanadium species in the electrolyte is relatively weak and it shows a slightly higher saturation for V(III), but this effect is outweighed by a stronger effect of compression. Synchrotron X-ray tomography highlights the occurrence of the Cassie-Baxter effect (the emergence of trapped air bubbles inside the electrode) and implies movement of these bubbles during continuous flow, in agreement with Greco et al.1. Figure 1: a) Saturation after injection of various electrolyte species into thermally activated carbon felt electrodes under different degrees of compression. b) Effect of compression on the pressure during the simulation of continuous flow-through conditions. The bar color corresponds to the color of the electrolyte solution in both figures. 1 Greco, K. V., Forner-Cuenca, A., Mularczyk, A., Eller, J. J. & Brushett, F. R. Elucidating the Nuanced Effects of Thermal Pretreatment on Carbon Paper Electrodes for Vanadium Redox Flow Batteries. ACS Applied Materials & Interfaces 10, 44430-44442, doi:10.1021/acsami.8b15793 (2018). 2 Bevilacqua, N., George, M. G., Galbiati, S., Bazylak, A. & Zeis, R. Phosphoric Acid Invasion in High Temperature PEM Fuel Cell Gas Diffsuion Layers. Electrochim. Acta 257, 89-98, doi:10.1016/j.electacta.2017.10.054 (2017). 3 Banerjee, R., Bevilacqua, N., Eifert, L. & Zeis, R. Characterization of carbon felt electrodes for vanadium redox flow batteries - A pore network modeling approach. Journal of Energy Storage 21, 163-171, doi:10.1016/j.est.2018.11.014 (2019). Figure 1

Investigation of hydraulic losses in a centrifugal pump with low specific speed

Investigation of hydraulic losses in a centrifugal pump with low specific speed

Understanding the Interplay between Electrolyte Velocity Distribution and Current Distribution in Vanadium Flow Battery Electrode

Vanadium redox flow batteries (VRFBs) are considered a promising candidate among grid-scale energy storage technologies due to their flexibility and scalability, high coulombic efficiency, and long cycle life. However, system costs and relatively low energy and power density compared to other electrochemical energy storage devices are major challenges to commercialization. At the cell level, mass transport losses are one of the major contributors to performance losses; this mechanism is associated with inadequate delivery of active species to electrode surfaces. Improving flow field design and electrode structure or simply increasing flow rate can mitigate mass transport losses. However, due to parasitic pumping losses, optimization is not straightforward. As yet unpublished research in our lab has shown that increased convection improves mass transport of the active species through the porous electrode and it is possible to achieve better electrochemical performance with lower pressure drop in convection-dominated VRFB cells. In this study, the impact of convection on electrochemical performance is investigated using computational fluid dynamics (CFD) model and in-situ localized current distribution diagnostics. Polarization curve analysis and pressure drop measurements are also used to support the conclusions. Experiments and simulations are conducted on strip cell architecture with varying channel depths (0.25, 0.50, 1.00, 2.50 mm) and flow rates (10-50 ml min-1). The simulation domain includes both channel and porous electrodes seen in Figure 1. Conservation of mass and momentum are solved to obtain velocity and pressure distributions. It is found that there is a strong relationship between electrolyte velocity in the electrode and electrochemical performance. Similar electrolyte velocity distribution (in the electrode) predicted for two configurations: 1 mm channel depth at 40 mL min-1 flow rate and 0.50 mm channel depth at 10 mL min-1 have similar polarization curves and current distributions down the channel. However, the model predicts very different velocity distributions for these configurations in channel. Higher velocity distribution predicted for 1 mm configuration has also higher pressure drop than 0.5 mm configuration. The results of the computational and experimental study as related to the trade-off between pumping power requirements and electrochemical performance in VRFBs will be discussed in this talk. Figure 1

Evaluating the thermal impacts and sustainability of intensive shallow geothermal utilization on a neighborhood scale: Lessons learned from a case study

This paper presents a case study using calibrated numerical models to evaluate the thermal impacts and long-term sustainability of intensive geothermal use on a neighborhood scale. The subsurface heat transport model is configured with site-specific parameters and validated against monitoring data from a typical urban living quarter in Germany. Based on the simulated ground temperature profile, the heat pump performance is approximated. In addition, the effects of groundwater flow on the thermal interaction and economical operation of the shallow geothermal systems are examined. The results indicate limited thermal impacts as the groundwater temperature will maintain above 3.2 °C and that the area undergone severe temperature drop is less than 1% size of the neighborhood. Since the estimated seasonal coefficients of performance (SCOPs) are at least 3.8, the sustainability of the shallow geothermal applications is confirmed economically. Nevertheless, financial disadvantages up to 92 € year-1 are anticipated due to gradual efficiency losses of the heat pump, which are meant for the owners of downstream installations. In addition, uncertainties in groundwater flow rate are also analyzed. For the negligible advection case, simulation results suggest that some systems can only operate sustainably for eight years. Conclusions are drawn regarding the general feasibility of neighborhood-scale shallow geothermal utilization and the importance of hydrogeological site investigations during the planning phase of such projects.

Diesel engine air path control based on neural approximation of nonlinear MPC

This paper deals with a control design problem for a diesel engine air path system that has strong nonlinearity and requires multi-input and multi-output control to satisfy requirements and constraints. We focus on a neural network based approximation of nonlinear model predictive control (NMPC) for high-speed computation. Most neural approximation methods are verified only through simulation; further, the influence of approximation on the closed-loop performance has been not sufficiently discussed. In this study, we discuss this influence, and propose a new method to improve stability against degradation due to an approximation error. The control system is assembled using a neural network based controller, obtained by the proposed method, and an unscented Kalman filter. This system is verified both numerically and experimentally; the results demonstrate the capability of the proposed method to track the boost pressure, EGR rate, and pumping loss according to the reference values, and satisfy the constraints of compressor surge and choke. The high computation speed that can be achieved using a standard on-board ECU is also demonstrated using the approximated controller.

Natural gas-diesel reactivity controlled compression ignition with negative valve overlap and in-cylinder fuel reforming

Dual-fuel reactivity controlled compression ignition combustion offers potentially superior overall efficiency and ultra-low nitrogen oxides and soot emissions. Using natural gas as the low reactivity fuel also provides high knock-resistance and carbon dioxide emission reduction. However, the concept suffers from relatively low combustion efficiency at low engine loads, causing unacceptable methane slip. This study tackles this issue, applying numerical simulations to investigate the application of negative valve overlap to improve combustion efficiency of reactivity controlled compression ignition at low engine loads. The objective is modification of in-cylinder thermal and chemical state before combustion, by varying timing and amount of fuel injected directly into the recompressed hot exhaust gases. The study uses TNO's multi-zone, chemical kinetics-based combustion model with variable valve actuation functionality. The simulation is based on two experimentally validated cases: an uncooled exhaust gas recirculation strategy and a lean burn concept. In both cases, negative valve overlap elevates in-cylinder temperature and cuts methane emissions by 15%, without combustion optimization. Crucially, it enables peak exhaust recompression temperatures above 850 K, sufficient for diesel reforming/oxidation. The lean RCCI strategy takes greater advantage of fuel reforming than the exhaust gas recirculation case. Optimum conditions give almost 99% combustion efficiency and ultra-low methane emissions. Net indicated efficiency is 40.5% (@15% load), despite negative valve overlap’s substantial pumping losses. Low-load net efficiency is 5.5 percentage points above the lean strategy baseline and 3 pp. better than the exhaust gas recirculation baseline. This strategy is considered applicable on state-of-the-art dual-fuel gas engines without hardware changes.

The effect of advanced ignition system on gasoline low temperature combustion

Engines operating in low temperature combustion during positive valve overlap operation offer significant benefits of high fuel economy over the low temperature combustion during negative valve overlap operation. Significant efficiency improvement was achieved by the increased gamma and lower pumping loss. However, NOx emissions were increased due to reliance on the flame-induced combustion. In this study, the corona ignition system was evaluated to reduce NOx emissions during positive valve overlap operation while maintaining the benefit of efficiency gain. The tests were performed in a 2.2-L multi-cylinder engine. The results show that the ignition delay is always shorter with the corona ignition system than with the spark plug. The corona ignition system is able to support stable combustion (coefficient of variation of indicated mean effective pressure <3%) in a lower load during positive valve overlap operation than the spark plug, which gives us additional efficiency benefit. Since the corona ignition system promotes simultaneous ignition of the mixture at multiple locations in the combustion chamber as opposed to ignition being limited to the spark gap channel, the dependence of the flame burn for stable combustion during positive valve overlap operation minimizes, which leads to lower NOx emissions over the spark plug.

Inverted Regulation of Multidrug Efflux Pumps, Acid Resistance, and Porins in Benzoate-Evolved Escherichia coli K-12.

Benzoic acid, a partial uncoupler of the proton motive force (PMF), selects for sensitivity to chloramphenicol and tetracycline during the experimental evolution of Escherichia coli K-12. Transcriptomes of E. coli isolates evolved with benzoate showed the reversal of benzoate-dependent regulation, including the downregulation of multidrug efflux pump genes, the gene for the Gad acid resistance regulon, the nitrate reductase genes narHJ, and the gene for the acid-consuming hydrogenase Hyd-3. However, the benzoate-evolved strains had increased expression of OmpF and other large-hole porins that admit fermentable substrates and antibiotics. Candidate genes identified from benzoate-evolved strains were tested for their roles in benzoate tolerance and in chloramphenicol sensitivity. Benzoate or salicylate tolerance was increased by deletion of the Gad activator ariR or of the acid fitness island from slp to the end of the gadX gene encoding Gad regulators and the multidrug pump genes mdtEF Benzoate tolerance was also increased by deletion of multidrug component gene emrA, RpoS posttranscriptional regulator gene cspC, adenosine deaminase gene add, hydrogenase gene hyc (Hyd-3), and the RNA chaperone/DNA-binding regulator gene hfq Chloramphenicol resistance was decreased by mutations in genes for global regulators, such as RNA polymerase alpha subunit gene rpoA, the Mar activator gene rob, and hfq Deletion of lipopolysaccharide biosynthetic kinase gene rfaY decreased the rate of growth in chloramphenicol. Isolates from experimental evolution with benzoate had many mutations affecting aromatic biosynthesis and catabolism, such as aroF (encoding tyrosine biosynthesis) and apt (encoding adenine phosphoribosyltransferase). Overall, benzoate or salicylate exposure selects for the loss of multidrug efflux pumps and of hydrogenases that generate a futile cycle of PMF and upregulates porins that admit fermentable nutrients and antibiotics.IMPORTANCE Benzoic acid is a common food preservative, and salicylic acid (2-hydroxybenzoic acid) is the active form of aspirin. At high concentrations, benzoic acid conducts a proton across the membrane, depleting the proton motive force. In the absence of antibiotics, benzoate exposure selects against proton-driven multidrug efflux pumps and upregulates porins that admit fermentable substrates but that also allow the entry of antibiotics. Thus, evolution with benzoate and related molecules, such as salicylates, requires a trade-off for antibiotic sensitivity, a trade-off that could help define a stable gut microbiome. Benzoate and salicylate are naturally occurring plant signal molecules that may modulate the microbiomes of plants and animal digestive tracts so as to favor fermenters and exclude drug-resistant pathogens.

Turbocharging of engines with low cylinder numbers: a thermodynamic consideration

In the present investigation, the influence of the number of cylinders on the turbocharger and the pumping losses were determined by extensive simulations in combination with experimental investigations. The turbine efficiency is influenced by the different pulsations as a function of the number of cylinders. In addition, another very serious influence of the number of cylinders on the pumping losses has been found. This effect depends strongly on the exhaust volume before turbine, which is why the topic of constant pressure and pulse turbocharging must be considered in detail. It has been found that a smaller number of cylinders (<4) has higher pumping losses in principle, even with the same turbocharger efficiencies. The lowest pumping losses can be achieved with four-cylinder engines. It has also been shown that this issue is completely different for diesel and gasoline engines.

The effects of residual gas trapping on part load performance and emissions of a spark ignition direct injection engine fuelled with wet ethanol

Biofuels, such as ethanol, have been introduced as a solution to decrease total CO2 emissions from transport sector as well as an alternative to increase the domestic energy security against international fuel price fluctuations. The use of high water content ethanol, the so-called wet ethanol (ethanol with higher than 5% water content v/v), has been proposed to reduce ethanol production cost. This work presents the application of wet ethanol on a naturally aspirated direct injection single cylinder research engine equipped with a fully variable electro-hydraulic valve train running on stoichiometric air/fuel ratio. The negative valve overlap (NVO) strategy was used to retain high residual gas fraction (RGF) at the part load operation of 3.1 bar IMEP and 1500 rpm. Anhydrous ethanol and different wet ethanol compositions (10% and 20% water-in-ethanol content v/v) were tested for several NVO durations, as well as European RON 95 gasoline. A one-dimensional engine model was built and validated against experimental data to estimate the RGF for each operating point. It was possible to achieve stable stoichiometric operation with more than 35% RGF for anhydrous ethanol and RON 95 gasoline. On the other hand, the maximum supported RGF for stable operation decreased as the water-in-ethanol content increased. The increase in water content reduced the tolerance to hot residuals due to lower combustion temperatures, which lengthened the flame initiation and main combustion phases. Even then, the increase in NVO period resulted in net indicated efficiency gains for all fuels due to less pumping losses, lower combustion temperature, and the possibility to maintain combustion efficiency at acceptable levels even with the maximum achievable RGF of each fuel. Anhydrous ethanol presented the highest net indicated efficiencies, while 10% water-in-ethanol mixture presented slightly higher indicated efficiency compared to gasoline. 20% water-in-ethanol mixture provided the lowest indicated efficiencies over the whole range of tested RGF.

Experimental study on combustion, emissions and thermal balance of high compression ratio engine fueled with liquefied methane gas

To improve the fuel efficiency of liquefied natural gas engine, an approach was proposed in our previous study, in which the liquefied natural gas is first purified into liquefied methane gas and then fueled to high compression ratio engine. To further evaluate the fuel efficiency of liquefied methane gas engine, in this study the thermal balance test was carried out, and then the thermodynamic performance of liquefied methane gas engine was analyzed and various kinds of energy losses were disintegrated. On this basis, the influence factors of various forms of energy flow in liquefied methane gas engine were discussed by combining with combustion and thermodynamics processes. Results show that, the proportions of indicated work in high-pressure cycle, exhaust energy and heat transfer loss are mainly influenced by engine speed. The high-pressure cycle efficiency increases with engine speed and the maximum value reaches 49.6% due to the higher compression ratio. The variation trend of exhaust energy proportion is similar as that of high-pressure cycle efficiency, while the proportion of heat transfer loss decreases with the engine speed increasing. Although the maximum high-pressure cycle efficiency appears in high speed conditions, the maximum effective thermal efficiency still appears at low speed due to the effect of friction loss and pumping loss (especially the former). Therefore, for the low speed conditions, the effective thermal efficiency of LMG engine can be further improved by optimizing the thermodynamic process (or combustion parameters); while for the high speed conditions, it is better to reduce the friction loss and pumping loss.

Effect of nozzle box arrangement on the aerodynamic performance of a single stage partial admission turbine

For partial admission turbine, nozzle box arrangement has a profound impact on its aerodynamic performance. Hence, a single stage partial admission turbine with two nozzle boxes under eight arrangements was numerically investigated using CFD of three-dimensional Reynolds-averaged Navier-Stokes and SST turbulence model. Additionally, the turbine at full admission was also studied for comparison. The results show that the extra losses including sector end loss, pumping loss and mixing loss caused by partial admission decelerate to increase with circumferential gaps between nozzle boxes. The detailed loss distributions with a different circumferential gap are illustrated. Moreover, the non-uniformity in static pressure, Mach number distributions and streamlines downstream the gap region are influenced obviously by circumferential gap. Multiple low Mach number lines formed by mixing effect between active fluid and stagnant fluid are also captured. Further, the analysis of excitation force shows that the circumferential gap also changes the blade tangential force and rotor radial force distributions significantly while the change of blade axial force and rotor axial force is relatively lower.

An assessment of the impacts of low-pressure exhaust gas recirculation on the air path of a diesel engine equipped with electrically assisted turbochargers

The impact of assisted boosting technologies on the ability to maintain desired exhaust gas recirculation is investigated. Regenerative electrically assisted turbocharging is a promising technique for significantly reducing turbo lag. In addition to mitigating turbo lag, assisted boosting systems also allow fuel economy benefits through reduced pumping losses. Pumping loss reduction is achieved through optimally managing the exhaust pressure via vane position (for a variable geometry turbocharger) or waste gate position (for a waste-gated fixed geometry turbocharger). The consequent loss in exhaust turbine power, from reduced exhaust pressure, is supplemented by electrical assist power. Reduced exhaust pressure and a rapid increase in intake pressure results in a pressure differential across the high-pressure exhaust gas recirculation valve that may not support exhaust gas recirculation flow demands. Hence, a natural trade-off exists between the reduction of pumping loss and the ability to meet exhaust gas recirculation demand, as dictated by prescribed constraints on engine-out emissions. Low-pressure exhaust gas recirculation offers a potential solution that may allow the desired fuel economy improvements without sacrificing the desired exhaust gas recirculation fractions in the intake charge. In this article, we consider this problem and investigate the potential benefits of using low-pressure exhaust gas recirculation for assisted boosted systems.

The Influence of Water and Mineral Oil on Volumetric Losses in the Displacement Pump for Offshore and Marine Applications

Abstract In this paper, volumetric losses in a positive displacement pump supplied with water and mineral oil are described and compared. The experimental tests were conducted using a prototype of a satellite pump (with a non-circular tooth working mechanism). In this paper, the sources of volumetric losses in this pump are characterized. On this basis, a mathematical model of these losses has been presented. The results of the calculation of volumetric losses according to the model are compared with the results of the experiment. Experimental studies have shown that the volumetric losses in the water pump are even 3.2 times greater than the volumetric losses in the oil pump. It has been demonstrated that the mathematical model describing the volumetric losses both in the water pump and in the oil pump is quite good. It has been found that the results from the loaded pump simulation (at ∆p=25MPa and ant n=1500rpm) differ from the results of the experiment by no more than 5% both for oil and water.

Thermal-hydraulic model for axial piston pump with leakage and friction and its application

PurposeThis paper aims to carry out a thermal-hydraulic simulation model for pump and hydraulic system to predict the temperature increasing and pump performance. Based on the model, how to alleviate the temperature is introduced. Besides, the optimization of piston is carried out.Design/methodology/approachThis paper analyzes the heat generation in lubricating interfaces of the pump with energy conversion theory. The heat transfer inside the pump is analyzed with the control volume method. The simulation model is constructed in AMESim because of its operating friendly nature. The experiment is carried out to prove the validity and accuracy of the simulation model.FindingsTemperature has less effect on the mechanical loss of pump. However, it has a great impact on volumetric efficiency. To reduce the temperature on the piston surface, the size of the piston should be optimized.Originality/valueThis paper fulfills a novel thermal-hydraulic model to evaluate the temperature of the pump. Based on the model, the performance of the pump is determined and optimization is carried out.

Progressive Familial Intrahepatic Cholestasis in Korea: A Clinicopathological Study of Five Patients.

BackgroundProgressive familial intrahepatic cholestasis (PFIC) is a heterogeneous group of autosomal recessive liver diseases that present as neonatal cholestasis. Little is known of this disease in Korea.MethodsThe records of five patients histologically diagnosed with PFIC, one with PFIC1 and four with PFIC2, by liver biopsy or transplant were reviewed, and ATP8B1 and ABCB11 mutation status was analyzed by direct DNA sequencing. Clinicopathological characteristics were correlated with genetic mutations.ResultsThe first symptom in all patients was jaundice. Histologically, lobular cholestasis with bile plugs was the main finding in all patients, whereas diffuse or periportal cholestasis was identified only in patients with PFIC2. Giant cells and ballooning of hepatocytes were observed in three and three patients with PFIC2, respectively, but not in the patient with PFIC1. Immunostaining showed total loss of bile salt export pump in two patients with PFIC2 and focal loss in two. Lobular and portal based fibrosis were more advanced in PFIC2 than in PFIC1. ATP8B1 and ABCB11 mutations were identified in one PFIC1 and two PFIC2 patients, respectively. One PFIC1 and three PFIC2 patients underwent liver transplantation (LT). At age 7 months, one PFIC2 patient was diagnosed with concurrent hepatocellular carcinoma and infantile hemangioma in an explanted liver. The patient with PFIC1 developed steatohepatitis after LT. One patient showed recurrence of PFIC2 after 10 years and underwent LT.ConclusionsPFIC is not rare in patients with neonatal cholestasis of unknown origin. Proper clinicopathologic correlation and genetic testing can enable early detection and management.

Experimental investigation on performance and economy characteristics of a diesel engine with variable nozzle turbocharger and its application in urban bus

Compared with the diesel engine with variable nozzle turbocharger, the performance and economy characteristics of diesel engine without variable nozzle turbocharger are experimentally investigated under various operating conditions in this paper. The diesel engine with variable nozzle turbocharger is employed to evaluate the effects of the opening degree on supercharging pressure, air flow, brake specific fuel consumption, smoke intensity and exhaust temperature of diesel engine. And the external and universal characteristics of diesel engines are also studied. The result shows that the variable nozzle turbocharger is beneficial to improve the performance and economy characteristics of diesel engine at the speed range of 900–1300 r/min. The experiments were carried out on the urban bus in Hezhou Road located in Guangxi Province (China) with engine of the YC6J200-42 series. The variable nozzle turbocharger can significantly optimize the performance and economy characteristics of whole vehicle, especially at low and medium speeds with lower smoke and nitrogen oxide emissions. Owing to the research data, the opening degree of variable nozzle turbocharger should be adjusted as much as possible to reduce the exhaust back pressure and pumping loss to improve the fuel economy of the engine.

Analysis of storage capacity and energy conversion on the performance of gradient and double-layered porous electrode in all-vanadium redox flow batteries

In the general monolayer electrode of constant porosity, the conflict between the available specific surface area and the hydraulic permeability is a momentous hinder in designing the high-performance electrodes of VRFB. In this paper, several novel electrode structures with gradient or double-layered porous media (GPM or DLPM) are installed in the stack to decouple the conflict and connection between hydraulic permeability and specific surface area. Ten kinds of electrode structures with constant, linear or stepwise decreasing/increasing porosity respectively are designed and compared. The lower concentration polarization loss, higher cell energy efficiency and capacity in the stepwise and linear increasing of porosity profiles are related to the electrolyte flow uniformity in porous electrode and alleviation of conflict between permeability and specific surface area. The higher pumping losses in these arrangements serve as deteriorative factor. In the stepwise increasing porosity mode, the effects of the thickness ratio between two porous layers with different porosities, electrode thickness and porosity variation amplitude were investigated. There is an optimum thickness ratio and electrode thickness to obtain the saturated cell capacity and more energy efficiency, and the rise amplitude of porosity will reduce the system efficiency while increasing the cell capacity.

The Effect of Channel Tapering on the Performance of Vanadium Redox Flow Batteries

The recent growth of intermittent renewable energy sources, such as wind and solar, requires a simultaneous growth of grid-scale energy storage facilities to provide energy resilience and reliability. Redox flow batteries (RFBs) are electrochemical devices that stand out as potential candidates for the storage of large amounts of energy in an economical and flexible way due to their ability to decouple power and energy capacity. However, one of the main drawbacks that hinders the widespread adoption of RFBs is their relatively low power density, which results in large stack size and high system cost. In recent years, the optimization of engineering aspects, such as electrode materials and cell architectures, has become a key element on the roadmap towards high-performance and cost-effective RFBs. For example, flow fields are critical components for the transport of active species to/from the electrochemically active area of the electrode (i.e., the surface area of the fibers) and, therefore, their design significantly affects the power output and efficiency of the system. In this work, the effects of interdigitated channel tapering on the performance of aqueous vanadium RFBs are examined experimentally, theoretically and numerically. Critical performance metrics, such as peak power density, limiting current density, round-trip efficiencies and pressure drop are obtained experimentally using flow cells with the tapered flow fields and compared to the ones obtained with the conventional (i.e., non-tapered) flow fields. To establish a fundamental understanding, the experimental results are further examined by means of a macroscopic multiphysics model. The initial results show that the use of novel flow-field designs can be an effective way to develop RFBs with superior performance, while maintaining pumping losses in acceptable levels. A mechanistic understanding on the transport behaviors and their coupling to the electrochemical performance will be provided.