Journal of Energy Engineering

To study the operational problems of an opposed firing boiler in continuously changing working conditions, the temperature, strain, and thermal stress of water walls were measured to analyze the distribution and relationship between temperature and deformation. The results showed that the asymmetrical arrangement of the burners in flexible operation can cause serious nonuniform distribution of the water wall temperature. The high temperature will induce extreme compressive stress, and the temperature difference between the high- and low-temperature areas will aggravate the tensile stress, which can induce bulge deformation and cracking of the water walls. We proposed replacing water wall plates with arc-shaped plates and adjusting the arrangement of burners to reduce the thermal stress. In addition, experimental equations were obtained between stress and temperature under steady and unsteady states by the least-squares method. These equations can be used to estimate the approximate range of high-stress areas based on the temperature of water walls. Finally, we found that the time hysteresis between temperature and thermal stress can be ignored. This study highlights the distribution and relationship of temperature and thermal stress on water walls under variable load conditions to guide their safe operation.

The combustion interactions during blended coal combustion affect their combustion characteristics, and the combustion interactions under air–fuel conditions have been well studied. However, oxy–fuel combustion considerably differs from air–fuel firing. Significantly, the $\mathrm{char}–{\mathrm{CO}}_2$ gasification reaction under oxy–fuel and high-temperature conditions substantially affects the combustion behaviors, which may influence the combustion interactions. This paper is to study the effect of the char oxidation and gasification reaction competition on comprehensive interactions in ${\mathrm{O}}_2/{\mathrm{CO}}_2$ mixture. The results show that under high-temperature and low-oxygen (${\mathrm{O}}_2<4\%$) conditions, an intense gasification reaction is observed. The competition between the $\mathrm{char}–{\mathrm{CO}}_2$ gasification and $\mathrm{char}–{\mathrm{O}}_2$ oxidation reactions influences the comprehensive interactions during blended chars combustion. As the $\mathrm{char}–{\mathrm{O}}_2$ oxidation reaction is strengthened and the $\mathrm{char}–{\mathrm{CO}}_2$ gasification reaction is weakened, the comprehensive interactions during blended chars combustion gradually decrease. Moreover, under the competition between the $\mathrm{char}–{\mathrm{CO}}_2$ gasification and $\mathrm{char}–{\mathrm{O}}_2$ oxidation reactions, only enhancing the $\mathrm{char}–{\mathrm{CO}}_2$ gasification reaction or enhancing the $\mathrm{char}–{\mathrm{O}}_2$ oxidation reaction weakens the comprehensive interactions. The weaker comprehensive interactions result in the smaller nonadditive behavior of the comprehensive combustion index. The findings shed light on the interaction effects observed during blended chars combustion, which can provide useful information to improve the combustion behaviors of the blended coals in oxy–fuel conditions.

The high-pressure injection strategy for di-n-butyl ether (DBE)-diesel fuel blends reduces particulate matter emissions. Exhaust gas recirculation (EGR) technology was used to decrease ${\mathrm{NO}}_x$ emissions. In this study, the combustion and emission characteristics of DBE blended fuel under the coupling of EGR and injection pressure (IP) were investigated using a turbocharged compression ignition (CI) engine. Furthermore, to understand the effect of fuel blends on particulate matter emissions, the emission levels of particulate matter were analyzed for four particle size ranges of different EGR, IP, and fuels. The results show that BD40 reduced CO emissions by 37.3% and soot emissions by 69.8% and increased ${\mathrm{NO}}_x$ emissions only slightly. The use of EGR significantly reduced ${\mathrm{NO}}_x$ emissions from DBE/diesel. The coupling of EGR with BD40 broke the ${\mathrm{NO}}_x$-soot emission balance. In addition, without EGR, BD40 reduced the $D_P<20\mathrm{nm}$ particle number concentration by 52.5% compared to D100. By increasing IP from 60 to 120 MPa, $D_P<20\mathrm{nm}$ particle number concentration of BD40 was reduced by 30.2%. Therefore, the use of 25% EGR and 120 MPa IP helps to decrease ${\mathrm{NO}}_x$ emissions, soot emissions, and fine particulate matter emissions of BD40.

Palm oil has significant potential for use as fuel for vehicles due to its abundance. However, it is highly viscous and has a high distillation temperature, such that it is difficult to use in engines. This study adds ethanol and gasoline to palm–diesel blends to improve their properties as engine fuel. Diesel, palm oil, gasoline, and ethanol can form transparent, homogeneous, and stable blended fuels at room temperature. D100 (pure diesel), D60P20G10E10 (60% diesel, 20% palm oil, 10% gasoline, and 10% ethanol by volume, denoted by D60P20), and D60P10G20E10 (60% diesel, 10% palm oil, 20% gasoline, and 10% ethanol by volume, denoted by D60G20) were used as test fuels in this study. Under the double injection strategy, the timing of the main injection was kept unchanged while the effects of different pilot injection timings were investigated by using pilot main intervals (PMIs). The results show that the diesel/palm oil/gasoline/ethanol (DPGE) blend as fuel had a longer ignition delay and shorter duration of combustion than D100. The peak heat release rate (PHRR) and peak combustion temperature (PCT) of D60G20 were the highest, followed by D60P20 and D100, at all engine loads. The DPGE blend reduced particulate matter (PM) emission and increased the emission of NOx, which is consistent with the variation in the PCT. With the increase in the PMI, the emission of PCT and NOx by the test fuels decreased slightly while the emission of soot decreased significantly. Of the test fuels considered, D60G20 delivered the best performance in terms of reducing PM emissions and has promising prospects for use in engines.

Providing an air cavity behind vinyl siding within a building envelope is an approach to mitigating building moisture-related issues, which also improves the building’s thermal performance. Previous studies commonly assume the cavity air as still and thus neglect the influence of mixed convection on the performance of the building envelope. Additionally, the air cavity is usually considered uniformly rectangular, neglecting the effects of its geometric irregularity and complexity. Therefore, to comprehensively investigate the effects of air cavities, this study analyzes ratios of siding depth to cavity depth in the mixed convection of air cavities, through rigorously formulating the problem and solving it using the perturbation method. The results show that increasing the ratio of the vinyl siding depth to the air cavity depth amplifies the metrics directly related to the energy performance of the building envelope, including the cavity air’s velocity, temperature, and mass fraction; the skin friction at cavity walls; as well as heat and mass transfer across the cavity. The effects of other critical parameters are also investigated, including the Reynolds number and temperature of the irregular cavity wall. This study provides guidance for comprehensively evaluating the thermal performance of an air cavity behind vinyl siding and improving the design of vinyl siding.

This study provides a solution to determine the porosity evolution of huge thick carbonates accurately using PetroMod version 2016.2 software with a cementation tool. The Lower Paleozoic carbonates from the Tazhong Uplift (Tarim Basin) were taken as examples. Results show that the errors of modeled porosity decreased from 256.3%–468.8% to 6.7%–12.5% for low-porosity carbonates and from 15.0%–22.9% to 2.9%–5.0% for high-porosity carbonates, indicating a better fit to the measured values after considering carbonate cementation. The calibrated model incorporating cementation exhibits typically low carbonate porosities and burial depths but high thermal conductivities, resulting in much lower formation temperatures, maturities, and hydrocarbon masses than the uncalibrated model. This study indicated that carbonate cementation plays a very important role in the reduction of carbonate porosity, and it is necessary to calibrate the thick-carbonate porosity model using the cementation tool. Although this method has certain feasibility and practicability and can be utilized widely to model huge thick carbonates, it has a limitation in recovering the increase in porosity caused by postdiagenesis.

The grid-scale battery energy storage system (BESS) plays an important role in improving power system operation performance and promoting renewable energy integration. However, operation safety and system maintenance have been considered as significant challenges for grid-scale use of BESS. Remaining useful life (RUL) is a useful indicator of the health condition of batteries but it is especially difficult to estimate because it is dependent on many monitoring quantities from BESS. This work presents a data-driven approach that is able to fully utilize BESS monitoring data obtained from the battery management system (BMS) in order to provide an accurate and robust estimation of RUL for each individual battery cells inside a BESS. Based on raw data from historical cycling records, the proposed approach employs elastic net regression to extract characteristic features from both primary and secondary data; a back-propagation neural network based model is then established to build the relationship of refined features and the resultant RUL. The effectiveness of the RUL predictor model is verified using a large-scale data set from real-world lithium-ion battery cells and expected to be applicable to practical grid-scale BESS.

An alcohol-based emulsified fuel is formed by mixing ethanol, biodiesel, and water in different proportions. This fuel can be used in internal combustion engines to reduce fossil fuel consumption. In high-temperature environments, the microexplosion phenomenon of alcohol-based emulsified fuel can be observed directly. In this study, a high-temperature fuel evaporation test device was set up. The microexplosion process of alcohol-based emulsified fuel with varying water content (0%, 1%, 2%, and 3%) in different temperatures (773 K, 873 K, and 973 K) was studied by high-speed photography, and the data were analyzed by morphological treatment. To evaluate the microexplosion characteristics of alcohol-based emulsified fuel, some kinetic parameters—such as microexplosion delay, mean interfacial tension, number of bubbles, and mean microexplosion intensity—were proposed. The results show that the kinetic parameters put forward in this paper are reasonable for evaluating the microexplosion process. If the water content in the alcohol-based emulsified fuel is kept the same, the microexplosion delay decreases, while the mean interfacial tension increases with increasing temperature. If the evaporation temperature is kept the same, the microexplosion delay and the number of bubbles increase with the content of water increasing. Within the range of tested content of water and temperature, the mean microexplosion intensity of emulsion fuel is 0.05366 $\mathrm{N}·{(\mathrm{m}·\mathrm{s})}^{-1}$ when the temperature is 973 K and the content of water is 3%, which is the largest.

Erosion wear is an important issue for a Francis turbine operating on rivers from the Himalayas, which directly hinders the utilization of hydropower. In this research, the severe erosion wear on the runner shroud of a Francis turbine is studied. The characteristics and physical mechanisms of the erosion wear on the runner shroud are investigated through numerical simulation using commercially available software. The results show that the runner shroud experiences heavy erosion wear, especially in the outlet region where the particle impact velocity is the fastest. The cross-flow and interblade vortex in the blade channel are major contributors to aggravating erosion on the shroud. They change the motion of the particle and cause more particles to accumulate on the shroud. Furthermore, this effect is ultimately attributed to the forces on the particle when moving in these flows. In the cross-flow, particles impact the shroud near the inlet at a slow velocity due to the drag force. In the interblade vortex, the slow particles are attracted to move around the vortex due to the fluid stress force and virtual mass force; when the particles are moving around the interblade vortex, they tend to impact the shroud at a high speed.

In order to obtain comprehensive fuel consumption of parts and systems in the energy transmitting process of plug-in hybrid electric vehicles, this work carried out an experimental study on energy flow of vehicles and made a comparison of vehicle performance and efficiency under different start states and state of charge (SOC) levels. The results show that the SOC has a major influence on equivalent fuel consumption against the way a vehicle starts, including cold and hot starts when the high-voltage battery has a low SOC level. Conversely, the start method plays a more important role in fuel efficiency for vehicles with high SOCs. In addition, the efficiency of engine and electric networks was also investigated. The results suggest that the highest brake thermal efficiency of 36% occurs when the vehicle is at a hot start and low SOC. This low SOC must be higher than the minimum limit. Also, motor efficiency increases with the increase of the SOC.

Analyzing the petrophysical properties of gas hydrate reservoirs under different conditions by experimental methods is time-consuming, costly, and very difficult. Therefore, it is of great practical significance to accurately reconstruct gas hydrate digital rocks using numerical simulation methods. In this study, based on in situ observations of gas hydrate pore habits and variation laws in the laboratory, a hybrid method was adopted to simulate pore-scale spatial distribution characteristics of gas hydrate using a digital rock model. The hybrid method combined classical nucleation theory, the diffusion-limited aggregation model, and the cluster-cluster aggregation model. Then, the pore size distribution, local porosity distribution, and average seepage probability distribution of gas hydrate digital rock and gas hydrate–bearing sediments were calculated and compared. In addition, the finite-element method was used to simulate and compare the reconstructed digital rock’s resistivity index and elastic modulus. The results showed that the hybrid method can effectively simulate the spatial distribution characteristics and variation laws of gas hydrate on the pore scale. In addition, the resistivity index and elastic modulus of the reconstructed gas hydrate digital rock were relatively close to those of gas hydrate–bearing sediments. However, compared with gas hydrate–bearing sediments, the average pore size of the reconstructed gas hydrate digital rock was smaller, and the pore connectivity showed a slight amount of difference. In summary, this investigation was of great significance in systematically studying the petrophysical properties of gas hydrate reservoirs.

The Xixiangchi Formation is a significant replacement stratum for natural gas production of deep marine carbonate in the Sichuan basin, which is mainly composed of grain shoal. Basic characteristics and corresponding major controlling factors of the Xixiangchi reservoir are of great importance for hydrocarbon exploration, but the diagenesis sequence and evolution of the reservoir are poorly understood because of their complexity. Based on core and thin-section observations, cathodoluminescence (CL), scanning electron microscopy (SEM), and microbiologically induced calcium carbonate precipitation (MICP) data, it is suggested that the Xixiangchi reservoir is comprised of medium crystalline dolostone and grain dolostone in the Central Sichuan basin, with an average porosity of 3.6% and 2.2%, respectively. The corresponding pore-throat type is an intercrystalline pore with a flaky throat and a dissolved intergranular pore with a necking throat. The majority porosity ranges from 2% to 4% (with a distribution frequency of 64.9%), but the permeability distribution is relatively scattered (with a distribution frequency between 10% and 30%). The capillary pressure curve of medium crystalline dolostone is characterized by coarse skewness, relatively flat plateaus, low displacement pressures, and high mercury saturation at relatively low injection pressures. The capillary pressure curve of grain dolostone is characterized by fine skewness, which exhibits relatively poor connectivity and a small value of median pore radius. The deposition of intraplatform grain shoals determines the original property of the Xixiangchi Formation reservoirs. Destructive diagenesis, including compaction and multistage cementation, decreases the physical properties of the Xixiangchi reservoir. Constructive diagenesis, including Caledonian supergene karstification and late-stage burial dissolution, tremendously improves the reservoir quality.

The air backflow in a Trombe wall has a serious offsetting effect on the ventilation performance. The air backflow always exists in areas outside the boundary layer. Therefore, the study of the characteristics of the boundary layer is of great significance to prevent the air backflow. In this study, mathematical models and simulation models are used to analyze the characteristics of the turbulent boundary layer, and the analysis results mutually verify the correctness. The boundary layer’s thickness decreases with the increase of heat flux and increases with the increase of surrounding temperature. The characteristics of the turbulent boundary layer obtained in this paper can be used to optimize the shape and structure of the Trombe wall to maximize the use of solar radiation.

For a diesel engine, it is crucial and difficult to reduce the original particle matter emissions. Although the emission of particle matter can be reduced effectively, the engine internal purification and external purification measures can increase the cost and manufacturing process. Therefore, designing and improving oil products has become the most effective way to reduce emissions. This study compared the combustion and particle matter characteristics of diesel, diesel–rocket propellant-3 (RP3) (WDBF) with 20%, 40%, and 60% rocket propellant-3 in a single-cylinder compression ignition engine. The brake power, brake thermal efficiency (BTE), and particle matter concentration of the diesel engine were determined experimentally at three speeds (2,000, 2,700, and $\mathrm{3,600}\mathrm{r}·{\min }^{-1}$) at engine loads of 10%, 50%, and 100%. The results demonstrated that with the increase of the RP3 blending ratio, the density, cetane number, kinematic viscosity, and surface tension of diesel–RP3 WDBF decreased, whereas the low heating value increased, and T10, T50, and T90 (10%, 50%, and 90% volume distillation temperatures, respectively) decreased. The addition of RP3 to diesel increased the peak number concentration of small particles under the test conditions. The total particle number concentration (TPNC), total particle volume concentration (TPVC), and total particle mass concentration (TPMC) decreased by 14.1%–53.4%, 22.5%–75.3%, and 21.3%–39.3%, respectively, compared with that of using diesel. The change was obvious with the increase of the RP3 ratio and without impact on brake power and BTE.

The horizontal axis tidal turbine is a typical apparatus to capture the energy in the ocean, but most traditional design methods of a turbine blade have led to the inefficiency of turbines. Therefore, to improve turbine efficiency, a design methodology of a horizontal axis tidal turbine blade based on bionics research is presented in this work. First, the point cloud of fin samples was scanned and processed. The three-dimensional digital models of pectoral and causal fins were extracted by reverse engineering software. Then, the bionic airfoil blade model was obtained through parameter optimization and coordinate transformation and a shark fin airfoil blade based on the bionic principle was designed, which provided a new method for the turbine blade design. Finally, the hydrodynamic performance of the bionic airfoil turbines at different pitch angles was studied through numerical simulations and underwater experiments, and the results showed that the performance of bionic airfoil turbines designed in this paper was better than that of the traditional blade turbines.

Dual-fuel engines can partially replace conventional diesel with alternative gaseous fuels and achieve lower smoke and nitrogen oxide (NOx) emissions. However, the fumigation of gaseous hydrocarbon fuels in dual-fuel engines results in high carbon monoxide (CO) and unburnt hydrocarbon (HC) emissions, particularly at low loads. In this work, a single-cylinder diesel engine was converted into a liquefied petroleum gas (LPG)-diesel dual-fuel engine. The engine performance and combustion characteristics have been studied along with the emissions of CO, HC, NOx, and smoke for 36%–64% LPG substitutions at 20%–70% loads. Reductions in CO and HC have also been studied with a commercial oxidation catalytic converter (OC) and a customized OC. The LPG-diesel dual-fuel engine operates efficiently with high LPG substitutions at 70% load. Without the use of the OCs, the LPG fumigation increases CO and HC emissions by up to 230% and 173%, respectively, with respect to diesel mode operations (single diesel fuel operations). The HC conversion efficiencies of the commercial OC are limited to approximately 60% at below half-load operations. However, the customized OC achieves HC conversion efficiencies of 77%–92% at 20%–70% loads, and the resultant HC emissions are 38%–87% lower than those of the diesel mode. Further, smoke emissions are 92%–96% lower than the diesel mode. The present study shows that the LPG-diesel dual-fuel mode can achieve CO, HC, NOx, and smoke emissions considerably lower than the diesel mode.

The Jiyuan oil field is a tight sandstone reservoir, and water injection does not effectively enhance the oil recovery. The microscopic seepage characteristics of water flooding are studied through physical and streamline simulation experiments. The results indicate that the piston-type displacement efficiency varies between 60% and 80%, and the nonpiston-type displacement efficiency reaches approximately 40%. The length of the horizontal section imposes the greatest influence on reservoir production, followed by the fracture length and the number of fracture segments, whereas the fracture conductivity impacts reservoir production the least. When the horizontal section length is 1,500 m, and the fracture length is 1,100 m, 5 fracture segments and 10 horizontal well clusters are adopted, and the conductivity of the artificial fractures reaches $200{\mathrm{um}}^2\times \mathrm{cm}$, while the oil field production efficiency reaches its maximum value. The preceding research results were applied in the Jiyuan oil field, and the results reveal that the initial well production increased by 47.06%, the decline rate decreased by 9.96%, and the well output increased by 19.1% during the stable production period. This research yields a reference significance for the efficient development of similar reservoirs.

The ignition and combustion characteristics of a single 20 (% by weight) Al/n-Heptane nanoslurry fuel droplet with oleic acid as surfactant was studied under the laser ignition model. The ignition delay time of the oleic acid/n-Heptane blended fuel droplet is lower than that of the n-Heptane fuel droplet, and its burning process is divided into three stages, namely, steady combustion of the n-Heptane, microexplosion combustion of the n-Heptane, and steady combustion of the oleic acid. When the laser hits the droplet of the oleic acid/n-Heptane, it has strong microexplosion and reburning. Compared with the oleic acid/n-Heptane droplet, the ignition delay time of the Al/n-Heptane nanoslurry droplet is significantly reduced and the burning time is slightly decreased, and the burning process only has two stages, i.e., microexplosive combustion stages of the n-Heptane and the oleic acid, respectively. When the laser hits the Al/n-Heptane nanoslurry fuel droplet, the morphology of the droplet that is heated by the laser but not ignited hardly changes during the falling process, while the morphology of the burning droplet changes greatly.