Journal of Energy Engineering

The effects of initial pressure, equivalence ratio, hydrogen fraction, and ${\mathrm{CO}}_2$ dilution ratio on the characteristics of ion currents and heat release rate (HRR) were comparatively investigated with natural gas as a fuel. Ion currents were measured with a central electrode; chamber pressure was measured with a pressure sensor, and HRR was calculated based on the measured pressure data. The feature parameters of the ion current and HRR correspond with each other; the start time, peak time, duration time, and peak values of the ion current and HRR have the same variation under the initial conditions. The interdependency between these parameters was discussed in detail. This study indicates that a good correlation exists between the characteristic parameters of the ion current and HRR under different initial conditions. The characteristic parameters of ion currents can be directly used to predict and analyze the HRR and the response dynamics of a flame in the combustion process.

Electrosprays of ethanol, 1-propanol and 1-butanol were studied experimentally at flow rates ranging from 5 to $25\mathrm{mL}/\mathrm{h}$, and voltages ranging from 3 to 6 kV, spraying along and against the direction of gravity. To study the general spray phenomenology and to provide measurements of the size and velocity of droplets, high-speed movies were taken of the light scattered by the spray from a planar laser sheet. Four modes of spraying were obtained when spraying along the direction of gravity. However, when spraying against the direction of gravity, another five modes were observed. The values of the measured velocities corresponded to low Reynolds numbers and low Nusselt numbers but high convective heat transfer coefficients. Electrical conductivity played a major role in bioalcohol electrospraying, but viscosity had a negligible effect. The possibility of coupling electrostatic spraying with combustion was established experimentally by performing burning experiments at 4 kV and $10\mathrm{mL}/\mathrm{h}$. Two distinct modes of flame were observed when burning the electrosprays, first a large diffusion flame and then a flat flame near the ground plate. The group combustion number calculation showed that the flame burned in a group combustion mode.

Coherency identification among generators plays an important role in controlled islanding and wide-area monitoring of a power system with renewable energy sources. So far, wide-area measurement systems (WAMS) have been deployed widely in power plants and key substations, so the trajectories measured by phasor measurement units (PMUs) and WAMS could be utilized to identify coherent generators (CGs). In this study, an algorithm for coherency identification among generators based on the fuzzy equivalence relation (FER) clustering method and synthesized weight is proposed. First, 10 indices for measuring the similarity of trajectories are presented. Then, the technique for order preference by similarity to ideal solution (TOPSIS) and a method based on entropy and multicorrelation coefficients is presented to determine the weight of each index for decision making of trajectory similarities. Next, the FER clustering method is proposed to cluster the trajectories and the $F$-statistics, which could measure the rationality of clustering results, is presented to determine the optimal cluster number of coherent groups among generators. Finally, the actual Guangdong power system in China, a revised 16-unit 68-bus power system, and the simplified China South Power Grid (CSPG) are used to demonstrate the effectiveness of the proposed methodology. Comparisons with some existing methods are performed and the impacts of integrated renewable energy generation sources on power system oscillations are also investigated.

Unitized regenerative fuel cells are unique devices that combine the functions of fuel cells and water electrolysis in one system. The internal mass-transport mechanisms present in a unitized regenerative fuel cell are closely related to the mode-switching method of the cell. A two-dimensional, single-phase, isothermal, multicomponent, and transient model was developed to investigate the characteristics of mass transfer coupled with electrochemical reaction in a unitized regenerative fuel cell under interval and continuous mode-switching methods. Results indicate that the average gas mass fractions in the gas-flow channel, gas diffusion layer, and catalyst layer are the same under the two different mode-switching methods. Gas mass fractions in different layers exhibit the same variation trend and gradient during the first and second cycles of interval and continuous switching. Under the two different mode-switching methods, the gradient of the gas mass fraction in fuel cell mode is larger than that in water electrolysis mode. The transient response of these layers under two different mode-switching methods is delayed by approximately 0.2 s compared with that of the operating voltage.

Thermal management is essential for the lithium-ion batteries of electric vehicles to maintain a suitable temperature range and reduce local temperature differences. In this study, a multichannel wavy tube is proposed for a liquid cooling cylindrical lithium-ion battery module. Three-dimensional (3D) transient simulations were conducted on the proposed battery module, and numerical optimizations were performed by varying the wavy contact angle and mass flow rate of the multichannel wavy tube. An increase in wavy contact angle and mass flow rate positively affects the heat dissipation efficiency and temperature field homogeneity of the battery module. However, the positive effects decline as the same amount of wavy contact angle or mass flow rate is increased because the wavy tube reaches its limit in cooling the battery module. Experiments under corresponding working conditions were performed to validate the heat transfer performance of the battery module. Simulation results will provide specific reference values for the thermal management of cylindrical lithium-ion battery modules.

Both experimentation and numerical simulations were conducted to study the effects of the overfire air (OFA) ratio on the coal combustion and ${\mathrm{NO}}_x$ generation characteristics of a 600-MW downfired boiler after changing the air distribution around the fuel-rich flow. In these experiments, the arrangement of the secondary air ports close to the fuel-rich flow was adjusted to modify the air distribution around the fuel-rich flow. The air distributions in the total air duct at OFA damper openings of 30%, 40%, 50%, 70%, 80%, and 100% were calculated by numerical simulation to determine the theoretical air ratios, and these values were in good agreement with experimental results. The calculated air ratios were used as the inlet boundary conditions in subsequent simulations of the boiler thermal states. The calculated ${\mathrm{NO}}_x$ emissions, carbon in fly ash, and gas temperatures in the lower furnace were also in good agreement with experimental data. Increasing the OFA damper opening from 30% to 80% generated both good flow and temperature symmetry while gradually reducing the airflow declination angles in the tertiary air regions, indicating reduced downward airflow depth. The flame kernel was also found to move upward. The OFA was readily drawn into the lower furnace at OFA damper openings below 50%, whereas larger openings gradually enhanced the OFA penetration. The corresponding experimental work demonstrated that increasing the opening from 30% to 80% increased the ${\mathrm{O}}_2$ concentration at the furnace exit from 3.02% to 3.51%, and ${\mathrm{NO}}_x$ emissions were decreased from 1,337 to $735\mathrm{mg}/{\mathrm{m}}^3$ at 6% ${\mathrm{O}}_2$. Reducing the outer secondary air while simultaneously increasing the secondary air ratio between the fuel-rich flow nozzles increased the carbon in fly ash from 4.93% to 5.75%. However, values of 5.94%–15.1% where obtained upon increasing the OFA damper opening from 0% to 70% in conjunction with prior secondary air distribution around the fuel-rich flow. Under these conditions, the coal burnout was greatly enhanced and the lower furnace temperature and ${\mathrm{NO}}_x$ emissions were slightly increased.

This paper examines the influence of wall reactions on the generation of the explosive time scale that characterizes ignition delay around the third explosion limit of a stoichiometric ${\mathrm{H}}_2/\mathrm{air}$ homogeneous mixture. The only wall reactions exhibiting a sizeable influence are ${\mathrm{HO}}_2\to {\mathrm{HO}}_2(\mathrm{w})$ and ${\mathrm{H}}_2{\mathrm{O}}_2\to {\mathrm{H}}_2{\mathrm{O}}_2(\mathrm{w})$—in both cases opposing the ignition process. The opposing influence of the former wall reaction complements that of $2{\mathrm{HO}}_2\to {\mathrm{H}}_2{\mathrm{O}}_2+{\mathrm{O}}_2$ in opposing ${\mathrm{H}}_2{\mathrm{O}}_2+\mathrm{H}\leftarrow {\mathrm{H}}_2+{\mathrm{HO}}_2$, which promotes ignition. However, the combined influence of these three reactions is not practically affected when the third explosion limit is crossed by increasing the initial pressure for a given initial temperature. The latter wall reaction opposes $2\mathrm{OH}(+\mathrm{M})\leftarrow {\mathrm{H}}_2{\mathrm{O}}_2(+\mathrm{M})$, which also promotes ignition. The combined influence of these reactions increases substantially as the third explosion limit is crossed, leading to significantly lower ignition delays. It is shown that around the third explosion limit the temperature has a strong influence on the explosive mode that leads to ignition. This influence is stronger when the wall reactions are accounted for.

This paper proposed a gas turbine and organic Rankine cycle (GT-ORC) combined cycle to further improve the energy efficiency of gas turbines. Alkanes, linear siloxanes, and aromatics were selected as working fluids for the bottoming organic Rankine cycle. Based on the mathematical model and solution procedure proposed, a thermodynamic comparison of GT-ORC combined cycle was conducted with pure and mixture working fluids. Simulation results showed that the mixtures made the combined cycle achieve higher efficiency than pure fluids. Compared with conventional steam Rankine cycles, the organic Rankine cycle had larger potential in recovering exhaust heat from gas turbines. The thermodynamic analysis showed that the thermal efficiency of the bottoming cycle increased with the rise of turbine inlet pressure. Besides, the ORC net power was maximum at the optimum turbine inlet pressure. Four commercial gas turbines with different exhaust temperatures (553–778 K) were also examined, and results indicated that the Trent 60 combined cycle achieved the highest thermal efficiency of 56.48%. For gas turbine of different power levels, the toluene/benzene mixture was more suitable in recovering waste heat from small and medium size gas turbines, while the cyclopentane was more applicable for microgas turbines.