Journal of Energy Engineering

Natural gas (NG) is a low-carbon fuel that can achieve low carbon emissions and high efficiencies. However, the low mean molecular mass and low energy density of methane result in low engine performance, and blending methane with gasoline is an effective way of improving the performance of NG engines. In this study, flame characteristics (including abnormal combustion) and engine performance are optically studied under methane port injection and isooctane direct injection conditions. The results indicate that the addition of isooctane can significantly increase the power output of NG engines. Under partial-load conditions, the minimum ignition advance for best IMEP is delayed with the addition of isooctane because of the higher flame speed of isooctane, and isooctane addition primarily improves the turbulent flame propagation rather than the initial flame formation. As for the isooctane injection timing, the indicated mean effective pressure (IMEP) first increases and then decreases with the delay in isooctane injection. The hot spots in the flame images confirm that late injection results in isooctane inhomogeneity, which reduces the engine’s thermal efficiency. At high loads, the low energy density of methane can lower the knocking intensity, even in the presence of auto-ignition at a speed of $120.7\mathrm{m}/\mathrm{s}$. The knocking pressure can lead to the ejection of oil droplets, which can increase the flame speed in the subsequent cycle.

With the development of renewable energy in power generation, a large number of thermal power plants operate under flexible working conditions. To study water wall deformation risk under flexible low-load conditions, a lab-scale opposed firing boiler was built to measure and analyze the temperature and thermal stress of the water wall under low-load flexible operating conditions with several nontypical burner arrangements. The results showed that flame radiation and flue gas convection heat transfer induced a high-temperature zone. Thermal stress was mainly caused by thermal expansion of the metal and expansion or extrusion deformation of other areas. Also, local thermal stress fluctuations and excessive values appeared under variable conditions. In addition, the burners’ symmetrical arrangement in the center effectively reduced thermal stress fluctuations and overall thermal stress under flexible working conditions. Finally, based on the limited temperature measurement points in this experiment, the optimal power parameter $\alpha$ for the inverse distance weighted (IDW) method and the shape parameter $\epsilon$ for the radial basis function (RBF) method were found to make a reasonable interpolation prediction of the temperature distribution of the water wall. This study highlights the recommended burner arrangements under flexible low-load conditions and the optimal parameters of the IDW and the RBF methods for estimating temperature in guiding safe operation of the water wall.

Cofiring sludge with coal based on existing power plants is a promising method to realize harmless recycling treatment for sludge disposal. However, the influences of sludge addition on ${\mathrm{NO}}_x$ emission are still controversial. Moreover, the optimal operating strategies for the cocombustion boiler need further investigations. In this study, the influences of sludge blending ratio, moisture content, sludge inlet position, and air-staging parameter on the combustion characteristics and ${\mathrm{NO}}_x$ emission behaviors in a 330-MW boiler were analyzed numerically. The results show that with the increase of sludge blending ratio, the flue gas temperature in the primary zone decreases. The overall burnout ratio declines with the addition of sludge due to the higher ash and moisture contents. Although the sludge contains more N than coal, the ${\mathrm{NO}}_x$ emissions in the cofiring case are lower than those in the coal-fired case due to the lower temperature and stronger reducing atmosphere in the primary zone. Reducing the moisture in the sludge is beneficial to the combustion within the furnace. Nevertheless, because of the higher temperature and lower CO concentration within the furnace, the ${\mathrm{NO}}_x$ concentration at the furnace outlet increases. For wall-fired boilers, feeding the sludge from the lower burners should be avoided considering the potential surge in ${\mathrm{NO}}_x$ emission. When the excess air ratio in the primary zone increases from 0.74 to 0.96, the ${\mathrm{NO}}_x$ concentration at the furnace outlet rises by 58%. Hence, although relatively lower excess air ratio in the primary zone could bring adverse impacts on the burnout behaviors, air-staging combustion is still necessary when cofiring sludge in the coal-fired boiler.

This paper describes the design and optimization of a cooling strategy based on a battery cooling system with indirect liquid-cooled plate heat exchange. The performance of the battery cooling system was analyzed using single-factor thermal simulation analysis. A cosimulation platform was built, and the rule-based multiparameter control strategy was used to design the heat dissipation logic, which was verified in the cosimulation platform. To improve the heat dissipation performance further, an orthogonal test (OT) was used to analyze the effects of different control parameters on each performance index during the battery discharge process, and the optimal combination of control parameters under a balanced multiobjective strategy was obtained. The results of the particle swarm optimization (PSO) algorithm with different weight coefficients were introduced for comparison. It was found that the OT and PSO can keep the temperature difference within the safe range. The maximum temperature was reduced by 3.57 and 4.10 K, respectively, and the average output power was increased by 11% and 9%, respectively, which indicates that the OT maintained good performance despite the significant workload reduction. The feasibility and reliability of the battery thermal management system control strategy optimized using OT were verified.

Using a newly developed thermo-linear swelling test, this work investigated the influence of temperature on shale swelling and shrinkage and Debye-Hückel length alterations within the diffuse double layer. Furthermore, the effect of temperature, dielectric constant of water, and ionic strength of aqueous solutions on the Debye-Hückel length and subsequent shale swelling and shrinkage was explored. It was found that, for dilute solutions, the product of temperature and dielectric constant of water ($T\times {\epsilon }_r$) did not considerably change for temperatures ranging from 25°C to 90°C. When shale communicated with 12% and 20% weight by weight (w/w) NaCl and ${\mathrm{CaCl}}_2$ solutions, the percent change in shale shrinkage as temperature incrementally increased from 25°C to 90°C is quite high and cannot be ignored. Results proposed that the dielectric constant of water may have been reduced by both temperature and ionic strength of solution, all of which caused a greater decrease in the Debye-Hückel length and consequent shale shrinkage. As for saturated NaCl and ${\mathrm{CaCl}}_2$ solutions, shale exhibited swelling performance at moderate temperatures (up to 50°C for NaCl and up to 70°C for ${\mathrm{CaCl}}_2$) followed by shrinkage afterward. This could be credited to the development of repulsive forces between similar ions within the diffuse double layer, which may have overwhelmed their electrostatic screening effect on charged clay surfaces. At higher temperatures, the influence of dielectric constant of water on the decreasing Debye-Hückel length may have softened the repulsion action generated by ions.

Air-breathing direct methanol fuel cells (AB-DMFCs) are used as a source of power for portable electronic devices. The width of the anode flow channel in AB-DMFCs plays a vital role in enhancing mass transfer to anode reaction sites. The transfer of oxygen to cathode reaction sites occurs through the current collector openings, and an optimum current collector open ratio (OR) was identified in this study. However, limited research is available on the effect of anode channel widths in combination with cathode current collector open ratios on the cell performance. This study analyzed the impact of anode single serpentine flow-channel widths and cathode current collector open ratios on AB-DMFC performance. The analysis was conducted in four stages. The first stage examined the influence of methanol concentration, varying from 0.5 to 2 M. In the second stage, three different anode flow-channel widths—1, 1.5, and 2 mm—were considered, with the methanol fuel flow rate varying from 0.5 to $2.5\mathrm{mL}/\min$. Experimental results revealed that fuel-cell performance increased with the increase of methanol concentration from 0.5 to 1.5 M and then decreased. Moreover, a fuel cell fitted with a flow field (FF) with a channel width of 1 mm provided better performance at a $2\mathrm{mL}/\min$ methanol flow rate. Three different open ratios of cathode current collectors—45.40%, 55.40%, and 63.05%—were considered in the experiment, and the ambient temperature was varied from 30°C to 70°C. Among the three current collectors, the cell with a 55.40% current collector offered superior performance, and the optimal condition was observed at a methanol flow rate of $2\mathrm{mL}/\min$. The optimized combination of a fuel cell fitted with a 1-mm channel–width flow field and 55.40% open-ratio current collectors produced a maximum power density (MPD) of $10.416\mathrm{mW}·{\mathrm{cm}}^{-2}$ at a $2\mathrm{mL}/\min$ methanol flow rate.

Water management plays a crucial role in the performance of proton exchange membrane fuel cells (PEMFC). In this paper, to speed up the removal of water in the flow channel, the microprotrusions are fabricated on the flow channel surface by using laser remelting, and the surface is then sprayed with nanohydrophobic materials. The contact angle of the surface after spraying the hydrophobic material and laser processing increases from 115° to 132° when only the hydrophobic material is sprayed. Through visualization experiments, the movements of droplets in the smooth and microstructured flow channel are compared at different gas inlet pressures and different water inlet mass flows. The results show that the contact form of droplets with smooth surface is a solid-liquid contact, whereas there is also a liquid-gas contact with a microstructured surface. The main movement form of droplets in the smooth flow channel is sliding, whereas in the microstructured flow channel it is rolling. Under different experimental conditions, the movement speed of droplets in the microstructured flow channel is faster than that of the smooth flow channel, which indicates that the flow channel with microprotrusions has a better drag reduction performance. As the gas inlet pressure increases, the initial diameter of the droplet gradually decreased, and the velocity of the droplet increases. The water inlet mass flow has little effect on the oscillation amplitude of the droplets in the smooth flow channel, whereas in the microstructured flow channel, the droplet oscillation amplitude increases with the increase of the water inlet velocity. This work provides a new choice for the design of a flow channel.

Abstract

The proton-exchange membrane fuel cell (PEMFC) bipolar plate serpentine flow channel U-shaped region is prone to the accumulation effect, which poses serious difficulties for fuel cell water management. As a result, a deep understanding of water transport in the U-shaped region is essential to improve the fuel cell performance. Under this direction, in this work, the impact of the different microstructure parameters and initial conditions on water transport in the U-shaped region was compared with and without microstructure using the volume of the fluid method. On top of that, the velocity field distribution in the $X$-direction and the pressure drop distribution in the flow channel were also analyzed. From the acquired results, it was demonstrated that due to the secondary flow caused by the bending property of the microstructure, the droplet movement time in the U-shaped region was significantly shortened after the microstructure was added in the U-shaped region. The initial conditions strongly affected the droplet motion, and a larger contact angle enhanced the wall hydrophobicity to facilitate the droplet discharge. An increase in the droplet diameter led also to a rise in the windward area and shear force, which shortened droplet discharge time. Interestingly, if the waveform microstructure has too-large crests, gullies will be created that will impede the droplet motion and increase the amplitude of the droplet oscillation, resulting in excessive pressure drop in the flow channel. A too-large period led to increased droplet momentum loss, whereas a short period reduced the wall contact angle, which is not conducive to drainage. The microstructure spacing significantly affected the droplet motion, and the reduced spacing increased the airflow diffusion effect to accelerate the flow rate. The main focus of this work was led on the application of the microstructure in a U-shaped region of the serpentine flow channel, which is of great specific significance for droplet removal inside the flow channel.

Practical Applications

Proton-exchange membrane fuel cells have the advantages of high energy efficiency and low emissions. They can directly convert chemical energy into electrical energy and have broad application prospects in many fields. There is a key component in a fuel cell called a bipolar plate. On top of them, different flow channels are formed through processing, and droplet accumulation is prone to occur at the corners of these flow channels. Therefore, solving the accumulation phenomenon is an effective way to improve the performance of fuel cells. By adding a microstructure design on the wall of the flow channel to change the internal droplet transport, the function of the microstructure is to accelerate the droplet discharge from the flow channel and improve the performance of the fuel cell. Therefore, this study will introduce how the internal water transport in fuel cell flow channels is influenced by the wall microstructure.

Abstract

The bipolar plate flow channels are critical to the operation of proton exchange membrane fuel cells (PEMFC). The appearance of a water flood phenomenon at the cathode flow channel affects mass transport capacity and output performance in the fuel cell. Based on the conventional parallel flow field (CPFF), multidimensional design is carried out to improve the comprehensive performance of the flow field. Auxiliary blockage flow fields (ABFF), auxiliary multiblockages flow fields (AMBFF), and auxiliary multiblockages tilt flow fields (AMBTFF) are proposed to overcome the previous concerns in this study. The mass transport of novel flow fields is studied based on fuel cell and electrolysis modules at CFD software FLUENT. The results indicate that multidimensional forced-convections formed in the cathode channel effectively promote both the entry of reactants and the removal of water, particularly in the under-rib region of AMBTFF. Therefore, the oxygen mass distribution in the cell is more uniform, which has a positive effect on the current density distribution, especially at the downstream. The current density in the AMBTFF is 11.1% more than that in CPFF. Moreover, the more stable operation of AMBTFF is confirmed due to the more uniform temperature distribution and the minimal increase of pressure drop.

Practical Applications

Proton exchange membrane fuel cells are devices that generate electricity through electrochemical reactions of clean fuels, with high efficiency, strong reliability, and zero pollution. It is widely used in equipment such as automobiles, ships, and portable power sources. Bipolar plates account for a significant proportion of the weight and cost of fuel cells, undertaking tasks such as fluid distribution, cooling, and heat dissipation. The flow field design of bipolar plate directly affects the heat and mass transfer capability and fuel cell output performance. The traditional flow field of proton exchange membrane fuel cells suffers from issues such inadequate mass transfer, internal flooding of the catalytic layer, and excessive temperature while operating at high current density. Novel multidimensional flow fields are proposed by this manuscript, which can improve the performance of proton exchange membrane fuel cells and further optimize material transport and drainage capabilities. The result can provide as new inspiration for proton exchange membrane fuel cell flow field design.

As a clean fuel with low carbon emissions, hydrogen-rich syngas has higher flame propagation speed and higher adiabatic flame temperature than other gaseous fuels, so its local flame propagation characteristics are also different from other fuels. In this paper, an experimental study on the hydrogen-rich syngas turbulent premixed flame was carried out at different pressures [101–303 kPa (1.0–3.0 bar)] when the hydrogen fraction was 65%, the fan speed was $\mathrm{3,559}\mathrm{revolutions}/\min$ (rpm), and the equivalence ratio was 1.0. The results show that with the propagation of the flame or the increase in pressure, the fluctuation amplitude of flame local radius and flame local pulsation radius becomes smaller. Similarly, the flame local propagation speed increases with the increase of pressure. By analyzing the correlation between the turbulent premixed flame front structure and the turbulent premixed flame propagation process in hydrogen-rich syngas, it is found that when the pressure increases, the correlation between the flame local pulsation propagation speed and the flame local pulsation radius weakens.

In the era of dominance of renewable energies and the pandemic-affected world, oil industries must produce oil from extant fields most economically. Further, increasing ecological awareness makes oil companies look forward to cost-effective, eco-friendly and efficient enhanced oil recovery (EOR) techniques like low-salinity water flooding (LSWF). The mechanism behind LSWF in the augmentation of oil recovery has been a prominent research area. The present study gives more profound insights into the impact of divalent cations (${\mathrm{Ca}}^{2+}$ and ${\mathrm{Mg}}^{2+}$) on LSWF in clayey sandstones by considering the multi-ion exchange (MIE) mechanism. The developed mathematical model consists of a fluid transport model, an ion transport module incorporating MIE, and a model for the weighing factor to interpolate between low-saline and high-saline states. The present model was validated and verified with analytical solutions and experimental results in the literature. In this study, the dilution of the ${\mathrm{Ca}}^{2+}$ ion concentration by a factor of $10$ and $100$ times of formation water in injection water led to an enhancement in desorption of ${\mathrm{Ca}}^{2+}$ ions and a relative increase in oil recovery by 9.61% and 12.33%, respectively. Further, the dilution of both ${\mathrm{Mg}}^{2+}$ and ${\mathrm{Ca}}^{2+}$ ions by 100 times led to the highest relative oil recovery of 13.22%. This study also provides fundamental insights into the microscopic displacement efficiency and fractional flow curves in the LSWF, which is a novel attempt. Moreover, this work helps in quantifying oil recovery in clayey sandstone reservoirs and also assists in selecting suitable reservoir candidates for LSWF.

The power output of proton exchange membrane fuel cells (PEMFCs) is built upon the uniform distribution of reacting gases and the mitigation of flooding of water on the cathode side of the fuel cell. This paper proposes a new flow field, which was modified from conventional serpentine flow fields (SFFs) by dividing the channel into three segments. In each of the segments, the flow channel length was decreased and increased gradually. This new modified flow field (MFF) was compared with SFF, both numerically and experimentally. Numerical and experimental investigations were carried out for an active area of $25{\mathrm{cm}}^2$. The MFF created an even distribution of gases and better water management than the SFF on PEMFCs. From the study, it is found that the new MFF improved power output compared to SFFs in numerical simulation and experimental analysis.

Thermal insulation coating is considered a low heat rejection technology for improving the thermal efficiency of engines in the future. A thermal-insulation-coated piston was used to reduce an engine’s heat loss; however, the piston temperature was increased notably for high-power engines. This increased wall temperature causes burning of the diesel spray. In order to analyze and improve the combustion quality of a high-power engine compounded with a thermal-insulation-coated piston, experiments and simulation methods were used in this research. The ultrahigh-pressure fuel injection system (up to 250 MPa) was applied to study the effect on combustion under high wall temperature and high-power conditions. A high wall temperature environment combustion image was achieved by visualization experiment in the constant volume combustion bomb. The thermal-insulation-coating and high-power engine condition can lead to ultrahigh wall temperatures. To study this kind of high wall temperature environment, the constant volume combustion bomb model was founded and calibrated. The effects of ultrahigh-pressure fuel injection and spray impingement distance on the combustion of high wall temperature were studied. The simulation results showed that the ignition delay is shortened, leading to more soot and longer combustion duration, which caused the combustion deterioration. With an increased fuel injection pressure and longer impinging distance, the combustion was improved. Moreover, the effect of increasing injection pressure on combustion is more obvious.

The complicated pore-throat structure of unconventional resource formations such as tight sandstones influences petroleum accumulation and even exploitation, because the pore-throat structure is difficult to mark. A pore-throat system was distinguished quantitatively utilizing high-pressure mercury (HPM), scanning electron microscopy (SEM), casting film, and rate-controlled mercury (RCM) methods. According to the analysis of the reservoir, the factors of differential accumulation of tight oil in Longdong and Northern Shaanxi were assessed. The results showed that lamellar throats and tube bundle throats were the primary types of throats in the study area. Tight sandstones from Longdong have a higher content of large throats than those from Northern Shaanxi, both with pore radii of 100–200 μm, whereas Northern Shaanxi has better pore-throat connectivity and better homogeneity of pores and throats. The fractal dimension of fine pores (D2) is significantly correlated with the pore-throat structure, including the median pressure and mercury saturation of macropore throats. Therefore, the pore-throat structure can be characterized by the fractal dimensions of small pores and throats. The continuous distribution of tight oil in Northern Shaanxi, with a higher degree of tight oil than Longdong, is positively related to the good pore-throat connectivity of the reservoir and the relatively small fractal dimension of the small throat. Thus, the differential accumulation of tight oil was influenced by the pore-throat connectivity and heterogeneity of the reservoir structure. The results of this study can be helpful in evaluating reservoir characteristics and selecting exploration zones.

Linear swelling and gravimetric ions and water uptake tests were experimentally conducted to examine the effectiveness of osmotically extracting water out of shale in the presence of dilute and concentrated salt solutions. In addition, vast data on shale’s membrane efficiency were collected from the literature to aid in this work. The main findings of this study confirmed that water transported into shale by diffusion osmosis may negate the benefits of water extraction out of shale by chemical osmosis. This is in line with previously reported results which suggested that shale acts as a nonideal leaky semipermeable membrane which allows ions to pass through. In addition, it was shown that shale swelling could occur due to diffusion osmosis and may dominate the swelling behavior of shale when it interacts with concentrated solutions. It was also shown that ion type and concentration could affect the amount of swelling that may be experienced by shale when exposed to salt solutions. Data from this work recommends incorporating dilute salt solutions in the make-up of drilling fluids to ensure that water extraction out of shale by chemical osmosis overtakes water flow into shale by diffusion osmosis. In addition, a critical salt concentration must be determined above which diffusion osmosis becomes dominant. The findings of this study can help us better understand the interaction between shale and drilling fluids and to improve drilling fluids design.

Underground hydrogen storage (UHS) and carbon dioxide capture and storage (CCS) have been the frontiers of energy transition of petroleum and coal industries. The similarities and differences of UHS and CCS are the key focus of this work. We first investigate the ${\mathrm{H}}_2/{\mathrm{CO}}_2\text{-}\mathrm{brine}$ flow characteristics in Berea sandstones applying our proposed pore-scale network modeling methods, emphasizing on the hysteresis of nonwetting phase. Then, the cap rock sealing capillary pressure curves are generated by scaling with the shale-gas-brine wettability conditions. Finally, the field-scale numerical models of ${\mathrm{H}}_2$ and ${\mathrm{CO}}_2$ injection processes are implemented based on the pore-scaled results, where the storage capacity and sealing security are focused. The simulation results imply that ${\mathrm{CO}}_2$ storage process has more potential of leakage happening, while the ${\mathrm{H}}_2$ storage is much safer since the cap rock sealing capillary pressure remains higher. Moreover, due to the extremely low viscosity and buoyancy effect, the gas front of ${\mathrm{H}}_2$ is sharper than that of ${\mathrm{CO}}_2$. The maximum injection volume of ${\mathrm{H}}_2$ is much lower than that of ${\mathrm{CO}}_2$ because ${\mathrm{H}}_2$ is less compressible at the subsurface conditions. In terms of storage capacity of finite saline aquifer, ${\mathrm{CO}}_2$ exhibits superiority over ${\mathrm{H}}_2$ storage. This study attempts to undertake the essential comparison of UHS and CCS in the way of multiscale numerical simulation methods and to propose the general rules of thumb for the related researchers.

The explosive mode that arises in the dynamics of the chemical kinetics term attracts particular attention because it is a mode that tends to drive a reacting system away from equilibrium. This is a slow mode that coexists with (1) a number of fast dissipative modes that tend to drive rapidly the system to equilibrium; and (2) a number of other slow dissipative modes, which compete with the explosive mode for the control of the system evolution after the fast modes become exhausted. Here, the proper context is established for the analysis of the explosive mode by accounting for the influence of all other modes present, both exhausted and active. It is shown that the analysis of an explosive mode is meaningful only when the fast dissipative modes become exhausted and this mode is among the slow modes that drive the system. The conclusions are highlighted through the analysis of a simple model.

With the global expansion of shale oil and gas exploration, analyzing the geochemical characteristics of different types of shale has seized extensive attention. Taking the Chang 7 Member and Shanxi Formation in the Ordos Basin as examples, this study investigated the geochemical and hydrocarbon expulsion characteristics of different types of shale. The results show that the Chang 7 shale is mainly type I. The total organic carbon (TOC) distribution of the Chang 7 shale in the study area was between 0.72% and 27.5%, with an average of 7.46%, and the vitrinite reflectance (Ro) ranged from 0.45% to 1.28%. It is a good source rock in immature to mature stages. The Shanxi shale is mainly type III. The TOC distribution of the Shanxi shale was between 0.6% and 58.5%, with an average of 8.92%, and the Ro distribution was between 0.42% and 2.39%, indicating good immaturity over mature source rock. The average hydrocarbon expulsion efficiencies of the Chang 7 shale calculated using the hydrocarbon generation potential method and the original hydrocarbon generation potential method were 82.49% and 94.81%, respectively. Simultaneously, a correlation analysis of hydrocarbon expulsion efficiency with organic matter abundance, maturity, and type found that when TOC was less than 5%, hydrocarbon expulsion efficiency increased with increased organic matter abundance and maturity. When the TOC exceeds 5%, the hydrocarbon expulsion efficiency is mainly related to maturity. The hydrocarbon expulsion efficiency of the sapropelic shale was much higher than that of the humic shale. This study is significant for evaluating shale gas and shale oil resources in similar areas.