Journal of Energy Engineering

Aim of this work is the evaluation of thermal behavior and performance of a conventional diesel oxidation catalyst (DOC) installed on an engine operating in dual-fuel diesel-methane conditions following a well-defined methodology conceived ad hoc. A catalyst was sized, realized, and instrumented with five thermocouples. Once mounted along the engine exhaust line, the test was run in order to determine several parameters characterizing the DOC behavior, such as downstream emission levels, conversion efficiency, thermal behavior, and light-off temperature. Tests have been performed varying the engine speed and substitution ratio in order to analyze the effect of these operating parameters on the behavior of the catalyst. The results indicate that, in dual-fuel conditions, the oxidation of species takes place in zones closer to the exit section, determining temperatures higher than those measured in conventional diesel combustion conditions at the same engine load. The light-off temperatures related to the conversion efficiency of unburned hydrocarbons and carbon monoxide both increase in dual-fuel conditions. The effect of substitution ratio results from the combined effects on combustion development together with engine-out concentration of long-chain and short-chain unburned hydrocarbons. The resulting effect is, on one hand, the reduction of unburned hydrocarbons light-off temperature as methane increases. On the other hand, carbon monoxide light-off temperature increases as methane increases due to the increased amount of engine-out hydrocarbons emissions. The reduction of engine speed determines the reduction of the temperature of the exhaust gases to the extent that the light-off conditions are sometimes not reached. Finally, a sensitivity analysis base on neural networks showed that, while less variables are sufficient for describing the behavior, in terms of carbon monoxide conversion efficiency, of a DOC mounted on an engine working in dual-fuel diesel-methane conditions, in case of unburned hydrocarbons conversion a set of more variables is required.

This work presents the computational investigation of the nonreacting flow field and of the fuel–air mixing characteristics in a stratified, premixer/bluff-body combustor configuration under the effect of elevated inlet mixture temperatures. Four levels of preheats of the inlet reactants are investigated, ranging from 300 to $743\mathrm{K}$, for lean to ultralean mixture settings. Different fuel–air mixing wake topologies were captured by regulating the fuel injection level, the incoming fuel–air ratio gradient, and the mixture preheat. An implicit, finite-volume-based large eddy simulation method was employed yielding satisfactory agreement between simulations and counterpart experimental data by successfully reproducing the large-scale features of the interaction of the primary afterbody recirculation with the incoming annular shear layer and the impact of preheat on the developing disk wake topology and fuel–air mixing performance. Thus, the effects of inlet mixture stratification, alone or in combination with inlet preheat, on the performance characteristics of the disk stabilizer were elucidated, while parameters controlling the fuel–air mixing in the recirculation zone and the near wake region were also characterized.

A 1D transient model was proposed to investigate the effects of the current density operating modes on the cold-start process of proton exchange membrane (PEM) fuel cells. The temperature evolution of the cell is solved by considering the reversible heat, reaction heat, Joule heat, and phase change heat. Four current density operating modes were studied based on this model: constant mode, gradually increasing mode, stepwise increasing mode, and zigzag mode. The results show that there is a threshold for the initial current density that influences the relationship between the successful cold start and current density. The cell can successfully start at a lower operating temperature by increasing the initial current density when the initial current density is below this threshold value. However, the lowest temperature for successful cold start increases if the initial current density exceeds the threshold value. Finally, a chart was plotted to indicate the regions of successful and failed self-start processes at different operating temperatures for the studied current density operating modes, respectively. The chart suggests that the cells with gradually and stepwise increasing current density modes have nearly equivalent cold-start performance, and are both better than the constant and zigzag modes.

Lithium-ion batteries are currently the most suitable power source for new energy vehicles. Thermal runaway is the biggest potential safety hazard. To achieve safer battery and battery design, it is necessary to fully understand thermal runaway. Here, a chemical-thermal coupled lithium-ion battery model is established. The temperature distribution rule of a lithium-ion battery surface in quantity–quality change under the influence of an external local high temperature heat source is discussed and analyzed using a multitime scale. The results show that lithium-ion batteries tend to thermal runaway when the temperature of external heat source is higher than a certain value. During this period, the most important thermal reaction is the reaction between anode and electrolyte.

The NET power cycle (NPC) offers an alternative way to inherently capture combustion derived ${\mathrm{CO}}_2$ with low efficiency penalty. This manuscript improves the NPC by recompressing a portion of the recycled ${\mathrm{CO}}_2$ stream to the exit of low temperate regenerator, forming a recompression NET power cycle (RNPC). The RNPC further enhances cycle recuperation and no longer needs to input extra heat to cover the heat gap between low pressure and high pressure ${\mathrm{CO}}_2$ streams in the regenerator. The model of internal convection cooling for the turbine in ${\mathrm{sCO}}_2$ cycle is also accomplished according to the semiempirical formula, aiming to investigate the effect of coolant flow. This manuscript respectively conducts the system multiparameter optimization for uncertain boundary parameters and the sensitivity analysis for definite boundary parameters. The simulation results show that RNPC can output $27.2{\mathrm{MW}}_{\mathrm{e}}$ more NEP than NPC without extra heat input, leading to 3.54% of the increase in net electric efficiency. RNPC’s efficiency increases monotonically with not only turbine inlet temperature but inlet pressure, which indicates that RNPC has the potentiality to further improve its efficiency at higher turbine inlet temperature and inlet pressure. However, turbine outlet pressure has a nonmonotonic effect on the cycle performance, and the optimal turbine outlet pressure corresponding to the maximum cycle efficiency is about 38–42 bar. The multiparameter optimization indicates that the global optimal cycle efficiency is approximately 53.55% within the ranges of investigated parameters. The RNPC’s efficiency is considerably influenced by the minimum cycle temperature ($0.234\%/°\mathrm{C}$), compressor efficiency ($0.08\%/\%$), turbine efficiency ($0.355\%/\%$), and regenerator temperature differences ($0.083\%/°\mathrm{C}$ for HTR and $0.080\%/°\mathrm{C}$ for LTR).

This paper focuses on a proton-exchange membrane (PEM) fuel cell/electrolyzer-based regenerative hybrid power system modeling and energy management for automotive application. In the regenerative hybrid power system, the fuel cell acts as the main power, and the battery, supercapacitor, and electrolyzer consist of a hybrid energy storage system (HESS) to provide and/or reclaim the extra power. To effectively distribute the hybrid power, the load power demand of the automobile is handled by using the wavelet transform based on the power change rate. The supercapacitor copes with the high power change rate load demand, and the low-slope portion is balanced by the fuel cell/electrolyzer and battery. To reduce the fuel consumption online, an improved rule-based energy management strategy (EMS) depending on dynamic programming (DP) allocation of fuel cell power and battery state of charge (SOC) is developed, and an electrolyzer operation strategy is also designed. The numerical simulation is implemented to test the proposed rule-based EMS, and the results indicate that the real-time control keeping 93.8% fuel consumption performance compared with the off-line global optimization solution in a given driving cycle.

Direct methane-to-methanol (MTM) conversion in a stepwise process under mild conditions has been widely studied. Nevertheless, suitable catalysts and reaction processes for industrial applications have remained elusive. Recently, small-pore copper-exchanged zeolites [copper ion–exchanged mordenite (Cu-MOR)] have been reported as the most effective catalysts for MTM reaction, which necessitates enhancement of active sites in the catalysts and protection of methanol from overoxidation. Herein, we attempt to optimize the catalyst material compositions of Cu-MOR and to optimize the pretreatment and reaction conditions during MTM tests. We investigated effects of copper composition, catalyst activation time, and activation temperature. Rationalizing the catalyst compositions and reaction conditions achieved methanol productivity as high as $0.107\mathrm{mol}/\mathrm{mol}$ Cu ($72.63\mu \mathrm{mol}/\mathrm{g}$ catalyst). We also simplified the catalyst treatment and reaction procedure, which resulted in methanol yield increase.

A better-designed flow channel can enhance the mass transfer and improve the performance of a proton exchange membrane fuel cell. An orientated-type flow channel can achieve guidance on reactant and product transfers, resulting in an increase in the mass transfer flux and the rapid removal of the product (especially liquid water). In this study, flow fields with different orientated-type gas flow channels having different baffles are fabricated, and their effects on the current density outputs of proton exchange membrane fuel cells under various heating temperature and reactant flow rate conditions are investigated using a self-constructed testing system. The experimental results indicate that cell performance can be increased when using orientated-type flow channels with baffles having longer leeward sides, and cell performance is increased more under a suitable heating temperature. Moreover, the increase in the current densities of proton exchange membrane fuel cells with smaller baffles is limited when increasing the reactant flow rates. This limitation can be avoided when using the orientated-type flow channels with baffles having longer leeward sides.

The redox flow battery is getting intense attention these days as one of the most promising systems to store energy generated from weather-dependent renewable energy sources such as solar and wind energies. In this research, the geometry-related performance of the hydrogen–iron redox flow battery is analyzed with five different flow-field geometries (parallel, serpentine, crisscross, interdigitated, and porous) to determine the best geometry leading to the maximum cell power and fuel efficiency. Diffusion-dominant flow-by mode, convection-dominant flow-through mode, and the hybrid combining both modes are investigated in detail to understand the characteristic transport modes of reactive species and underlying flow physics. In particular, the effects of the flow geometries are analyzed with respect to system-based as well as cell-based performance. It is found that the best net power gain is achieved from the porous flow field, which has excellent fuel utilization and cell power with a low electrolyte supply rate.

The autoignition dynamics of a three-component surrogate jet fuel (66.2% n-dodecane, 15.8% n-proplylbenzene, 18.0% 1,3,5-trimethylcyclohexane) suitable for usage as Jet A-1 and RP-3 aviation fuels are analyzed, using the detailed mechanism of Liu et al. (2019). The conditions considered are relevant to the operation of gas turbines and the analysis is performed using mathematical tools of the computational singular perturbation (CSP) method. The key chemical pathways and species are identified in the analysis of a homogeneous adiabatic and constant pressure ignition system for a wide range of initial conditions. In particular, the key role of hydrogen and CO-related chemistry is highlighted, with an increasing importance as the initial temperature increases. The ${\mathrm{C}}_2{\mathrm{H}}_4\to {\mathrm{C}}_2{\mathrm{H}}_3\to {\mathrm{CH}}_2\mathrm{CHO}$ pathway is also identified as playing a secondary but nonnegligible role with an importance increasing with initial temperature, favoring the system’s explosive dynamics and, thus, promoting ignition. Finally, ${\mathrm{C}}_2{\mathrm{H}}_4$ is identified as being a species with a key (secondary) role to the system’s explosive dynamics, but its role is replaced by ${\mathrm{C}}_3{\mathrm{H}}_6$ and, eventually, by ${\mathrm{O}}_2$ as the initial temperature increases. In the second part of the current work, a 58-species skeletal mechanism is generated using a previously developed algorithmic process based on CSP. The developed skeletal mechanism was tested in a wide range of initial conditions, including both ignition delay time and laminar flame speed calculations. For the conditions that were of interest in the current work, the skeletal mechanism approximated the detailed mechanism with very small error. The 58-species skeletal mechanism is shown to be ideal for use in computational fluid dynamics applications not only because of its small size but also because of its sufficiently slow associated fast timescale.

Metal-organic frameworks (MOFs) are perhaps one of the promising candidates for ${\mathrm{H}}_2$ storage in a fuel cell vehicle. However, impurity gases, such as ${\mathrm{H}}_2\mathrm{O}$, ${\mathrm{CO}}_2$, ${\mathrm{CH}}_4$, ${\mathrm{O}}_2$, and ${\mathrm{N}}_2$ existing in the process of ${\mathrm{H}}_2$ production, have a detrimental impact on ${\mathrm{H}}_2$ storage. In the present work, the process of ${\mathrm{H}}_2$ with and without impurity gases (i.e., ${\mathrm{H}}_2\mathrm{O}$, ${\mathrm{CO}}_2$, ${\mathrm{CH}}_4$, ${\mathrm{O}}_2$, and ${\mathrm{N}}_2$) adsorption in 95 MOFs is screened by molecular simulation. The effect of a low concentration of impurity gases on the ${\mathrm{H}}_2$ delivery capacity is studied. The results show that the effect of impurity gases on the ${\mathrm{H}}_2$ delivery capacity of 95 MOFs ranks as ${\mathrm{H}}_2{\mathrm{O}>\mathrm{CO}}_2{>\mathrm{CH}}_4{>\mathrm{O}}_2{=\mathrm{N}}_2$. DIDDOK is demonstrated to exhibit the best gravimetric delivery capacity of ${\mathrm{H}}_2$, and ANUGIA exhibits the best volumetric delivery capacity of ${\mathrm{H}}_2$. These results show that one should consider impurity gas effects during screening the best adsorbent for ${\mathrm{H}}_2$ storage in fuel cell vehicles.

As the most critical part of a hydropower station, reversible pump–turbines (RPTs) are facing the trend of high parameterization (e.g., high head and high rotation speed) with the rapid development of hydropower, which may cause more detrimental cavitation-induced hydrodynamic forces. Considering that cavitation occurs more easily under pump mode than turbine mode for the RPT, the characteristics and generation mechanism of the hydrodynamic radial force induced by cavitation of a RPT model at pump mode are investigated by computational fluid dynamics and experimental methods. Combined with the shear stress transport (SST) turbulence model, the three-dimensional (3D) unsteady Reynolds-averaged Navier-Stokes (URANS) equations are solved to calculate the cavitation flow of the RPT at various cavitation states. The blade loading and the pressure pulsations of the pressure/suction surfaces of the blade are monitored from the inlet to the outlet. Results show that with the development of cavitation, increasing cavitation bubbles covering the blade surfaces lead to the decrease of the blade loading, weaken the regularity of the pressure fluctuation, and increase the amplitude of the pressure pulsation, especially the suction surface. Furthermore, the characteristics of hydrodynamic radial forces under various cavitation states are discussed, and it is found that the values of the hydrodynamic radial forces become larger and the alternating hydrodynamic radial forces are more remarkable with the development of cavitation. Meanwhile, the symmetry of the radial force of the impeller presents a slight change due to the rotor–stator interaction between impeller and guide vanes and the symmetrical structure of the guide vanes. Then, to explore the generation mechanism of the hydrodynamic radial forces, the frequency spectrum of the pressure pulsation and hydrodynamic radial forces are analyzed comparatively. It is found that the hydrodynamic radial forces are affected by the rotor–stator interaction in the initial stage of cavitation, whereas the influence of the pressure distribution of suction surface of the blade increases with the development of cavitation.

The solar-powered Organic Rankine Cycle (ORC) could solve the energy crisis and achieve low emissions because it presents a high energy conversion efficiency for a low-temperature heat source, with little impact on the environment. This paper investigates a solar-powered ORC that applies a compound parabolic collector (CPC) and a thermal storage unit for collecting solar radiation and achieving the continuous system operation, respectively. According to the established mathematical model, the effects of thermodynamic parameters on system performance are analyzed. In addition, a multiobjective optimization is performed to find the optimal key parameters and obtaining the optimal system performance from both thermodynamic and economic perspectives by employing nondominated sorting genetic algorithm II (NSGA-II). The results reveal that increasing the turbine inlet pressure, thermal oil mass flow of vapor generator, and CPC and decreasing the cooling water temperature could improve system performance. The optimization results show that the optimum solution is obtained with an average net power output of 143.02 kW and a daily average exergy efficiency of 7.75% under the given conditions. The corresponding values of the selected decision variables—turbine inlet pressure, thermal oil mass flow of CPC, thermal oil mass flow of vapor generator, and terminal temperature difference of condenser—are 1,999.611 kPa, $12.00\mathrm{kg}·{\mathrm{s}}^{-1}$, $5.97\mathrm{kg}·{\mathrm{s}}^{-1}$, and 14.02 K, respectively.

Ethanol alternating current (AC)-manipulated electrosprays were investigated for a frequency range of $0.1–10\mathrm{kHz}$; applied RMS voltages 3, 4, 5, and 6 kV RMS; and flowrates 5, 10, 15, 20, and $25\mathrm{mL}/\mathrm{h}$ with the purpose of determining spray phenomenology as well as the differences with DC-manipulated e-sprays. Five dominant modes were observed, dripping, cone-jet, multijet, ramified-jet, and spindle mode, of which the ramified jet is specific to AC manipulation. The AC electrosprays demonstrated pulsating spray behavior, with hopping between modes for some cases. The conditions under which each mode appeared were determined in terms of electric bond matter and nondimensional flow rate. It was also shown that the frequency of the applied AC field could couple with the ohmic charge relaxation time in the liquid, as well as with the ionic charge injection time in a way that determined the cycling frequency of the electrosprays.

The fuel octane number affects the fuel consumption and emission characteristics of vehicles powered by spark-ignition engines. An investigation on the effects of commercial types of gasoline with different research octane numbers (RON) on a vehicle’s performance can provide valuable insights and guidelines for the further improvement of the engine and fuel design. In this work, three commercial-types of gasoline with RON values of 92, 95, and 98 were tested in two compact passenger vehicles. One vehicle is equipped with a gasoline direct injection (GDI) engine with a 1.4-L displacement and a turbocharging system, and the other one is equipped with a port fuel injection (PFI) naturally-aspired engine with a 1.6-L displacement. The new European drive cycle (NEDC) was used to test the effects of three gasoline fuels on both vehicles. The experimental results show that for the vehicle equipped with the GDI engine, with the increase of the RON number, the fuel consumption, carbon dioxide (${\mathrm{CO}}_2$), and carbon monoxide (CO) emissions increase first and then decrease. The total hydrocarbon (THC) and particulate matter (PM) emissions decrease first and then increase, while the NOx emissions increase gradually; the differences between the maximum and minimum values in the fuel consumptions and the emissions of NOx, CO, THC, ${\mathrm{CO}}_2$, and PM are $0.1\mathrm{L}/100\mathrm{km}$ (1.7%), $57.54\mathrm{mg}/\mathrm{km}$ (4.5%), $119.26\mathrm{mg}/\mathrm{km}$ (3.3%), $21.73\mathrm{mg}/\mathrm{km}$ (2.3%), $2.55\mathrm{g}/\mathrm{km}$ (2.0%), and $0.24\mathrm{mg}/\mathrm{km}$ (20.6%), respectively. For the vehicle with the PFI engine, with the increase of the RON number, the fuel consumption decreases, the ${\mathrm{CO}}_2$ and THC emissions decrease first and then increase, and the CO emission increases first and then decreases, while the NOx and PM emissions increase gradually; the differences between the maximum and minimum values of the fuel consumptions and the emissions of NOx, CO, THC, ${\mathrm{CO}}_2$, and PM are $0.18\mathrm{L}/100\mathrm{km}$, $18.19\mathrm{mg}/\mathrm{km}$ (1.1%), $84.82\mathrm{mg}/\mathrm{km}$ (1.6%), $21.06\mathrm{mg}/\mathrm{km}$ (3.1%), $1.36\mathrm{g}/\mathrm{km}$ (0.9%), and $0.47\mathrm{mg}/\mathrm{km}$ (50.9%), respectively. It can be seen that different RONs lead to the variation in fuel consumption and emissions in an NEDC test. In terms of acceleration performance, the impact of different fuels is considered to be only marginal because the variation in the acceleration time due to fuel effects is less than 2%.

Previous studies have shown that predrying can improve lignite combustion performance and lignite-fired boiler efficiency. This paper numerically investigated the effect of the lignite predrying degree on the combustion and ${\mathrm{NO}}_x$ generation characteristics in a 600-MW lignite-fired boiler. The simulation models were firstly validated by the design value and part of the in situ data of the boiler, and then, the effects of the lignite predrying degree on the velocity, volatile distribution, combustion, and ${\mathrm{NO}}_x$ generation were conducted. The results show that the moisture content of lignite affects the devolatilization, ignition, combustion, and ${\mathrm{NO}}_x$ generation processes because moisture evaporation changes the temperature distribution. In addition, the NO concentration in the burnout zone is higher than that in the main combustion zone, which is different from the distribution of NO in a bituminous-coal-fired boiler. When the moisture content of lignite decreases, the devolatilization and ignition rate increase, the combustion intensity and flue gas temperature increase, and the NO production and the heat transfer between the flue gas and the water-cooled wall increase as well.

Taking inspiration from one of the most significant experiences of coal and biomass cogasification, such as that undertaken in the Willem-Alexander Centrale (WAC) power plant located in Buggenum, Netherlands, a modeling procedure was conceived to simulate the operation of an integrated gasification combined cycle (IGCC) power plant with different types of fuel, spanning from 100% coal to a mixture of 30% coal and 70% biomass. After a careful validation based on the experimental data currently available in the published literature, the IGCC modeling was combined with an optimization method through the use of the commercial code Thermoflex. The main goal was to find the coal/biomass mixture allowing for a twofold purpose: an effective reduction in carbon dioxide emissions, on the one side, to mitigate global warming, and an increase in the hydrogen content of syngas, on the other side, for potential economic benefits in the context of polygeneration. Different kinds of coal and biomass were taken into account, with a wide range of lower heating value (LHV). The results were found to be strongly dependent on the energy content of the selected coal/biomass blends. Overall, the optimized solutions resulted in a loss of net electric efficiency compared to the design performance with 100% coal firing.

Electric vehicles use lithium-ion batteries as their power source; however, many researchers have expressed concern about the safety of these batteries. In this study, a new method was used to establish an accurate model of a lithium-ion battery, which can be used to calculate the heat production of lithium-ion batteries and the change in lithium-ion concentration. The effect of local heat accumulation on the thermal characteristics of lithium-ion batteries was studied. The electrochemical heat generation and side-reaction heat generation of lithium-ion batteries under rates of 1C, 3C, and 5C were compared (C-rate is the measurement of the charge and discharge current with respect to its nominal capacity). The results show that adding the heat source during charging can reduce electrochemical heat generation but increase side-reaction heat generation. At the same time, adding heat will accelerate the precipitation of a lithium-ion battery, improving the overall temperature of the battery.