Journal of Energy Engineering

The interaction of an axisymmetric, bluff body-stabilized, primary zone, operated under stratified inlet mixture conditions, with a coannular, secondary swirling stream and an external, surrounding air coflow was investigated. The coannular assembly establishes an axial sequence of two recirculations, the bluff body zone and the adjacent swirl-induced vortex breakdown region that promotes mixing of the combustion products with the swirl stream. The rate and efficiency of admixing of primary, secondary, and external stream gases and the entrainment behavior of the twin vortex system was studied for inert conditions, under different inlet settings and combinations of fuel injection placement in either the primary or swirl stream. The counterpart lean and ultralean reacting wakes were then studied to appraise the capacity of the system to regulate effectively the primary combustion process. Measurements of fuel-air mixing concentrations, temperatures, chemiluminescence imaging of ${\mathrm{OH}}^{*}$ and ${\mathrm{CH}}^{*}$, and gas analysis assisted in this preliminary evaluation of the variations in flame structure, mixing topology, and combustion performance. Complementary computations of the mixing fields were performed to provide insight into the flow patterns that support flame stabilization. The differences and similarities between the present flame stabilizing configuration and other types of axisymmetric arrangements are also highlighted and discussed.

Energy and exergy analyses of a recompression supercritical carbon dioxide Brayton cycle integrated with a solar tower through a two-tank thermal storage system were conducted. A complete mathematical model, where a heliostat field was deployed and annually optimized is presented. This optimized heliostat field was then integrated with the supercritical carbon dioxide (${\mathrm{sCO}}_2$) recompression Brayton cycle through a two-tank thermal storage system. Finally, exergy analysis was conducted for the entire integrated system. Molten salt was used as the medium in the storage tanks, and the analysis was performed for June 11, March 16, and December 10. The analysis was conducted for each complete day so that the storage system operated for 24 h without the need for any auxiliary heat source irrespective of the net power output of the integrated system. It was concluded that the highest and the lowest exergy destruction occurred in the central receiver system and the thermal storage system, respectively. For the month of June, the exergy destruction rate for the heliostat field and the solar tower is 1,295,605 and $\mathrm{156,254}\mathrm{kWh}/\mathrm{day}$, respectively, which together constitute the total exergy destruction of the central receiver. In addition, the combined exergy destruction of all the components of supercritical carbon dioxide Brayton cycle is $\mathrm{138,432}\mathrm{kWh}/\mathrm{day}$, and for thermal storage the exergy destruction rate is $\mathrm{4,735}\mathrm{kWh}/\mathrm{day}$. Furthermore, the net energy efficiency of the whole system at solar noon for the month of June, March, and December is 6.93, 5.71, and 4.45%, respectively. Lastly, the electrical second law efficiency is 7.44, 6.14, and 5.04% for the months of June, March, and December, respectively. This analysis was conducted for Dhahran, Saudi Arabia, as an illustrative example of the developed model.

Electricity and freshwater are fundamental demands both for life consumption and industrial production. In this paper, a power and water combined system is proposed, with a humidification dehumidification (HDH) desalination unit coupled to a top organic Rankine cycle (ORC), and the condensing heat from the turbine exhaust is absorbed by the seawater to drive the desalination system. Based on the mathematical models of the combined system, energy and exergy analysis is achieved. After the detailed calculation for the heat and mass transfer characteristics, the system cost is also illustrated to present the economy of the system. The results show that peak values for the output power, 9.51 kW, and freshwater production, $262.97{\mathrm{kg}\mathrm{h}}^{-1}$, can be obtained when an evaporation temperature of R245fa, 380.15 K and balance condition of the dehumidifier, arrive simultaneously. The corresponding values of gained output ratio (GOR), 1.66, and efficiency, 1.59, with a minimum specific exergy, $250.46{\mathrm{kJkg}}^{-1}$, indicate the best energy utilization within the combined system. It can be concluded that the characteristics of the dehumidifier are more important because of the value elevation for GOR to 2.05, and declination of specific cost for heat and mass transfer area to $49.24\yen {\mathrm{t}}^{-1}\mathrm{h}$, while the effectiveness of the dehumidifier is raised from 0.85 to 0.9.

A new type of solar-aided power generation plant has been proposed and numerically analyzed in this work. It is composed of a parabolic trough collector field, based on gas-phase nanofluid, coupled with a flameless coal burner. In this system, high-temperature solar thermal energy is used to preheat combustion air before it is sent to the burner. In the first part of this study, the solar field was sized in order to optimize its performance in coupling with the coal-fired power plant. The simulations, which resulted in 2,585 feasible solutions, explained the relationship between solar energy introduced into the burner, the parabolic trough collector field surface, and heat storage mass. In the second part of this work, a computational fluid dynamics analysis of the coal burner was carried out, in order to reach, as much as possible, a flameless operating condition, assuming provision of solar energy to the burner. At the same time, in order to keep the final flame temperature and the overall heat exchange conditions unchanged, it was considered useful to increase the external exhaust gas recirculation fraction in equal measure with the increase of the thermal input. The computational fluid dynamics analysis demonstrated that the increase in the temperature of the combustion air, due to solar input, intensifies the staging effect. In addition, the recirculation zone (more intense), resulting in flame shortening and rapid mixing of reagents and combustion products, yielded very uniform conditions in terms of chemical species and temperatures in the rest of the combustion chamber. All this contributed to a significant reduction in terms of NOx emission.

This work investigated the thermal management of Li-ion battery packs by using reciprocating cooling and heating systems with different reciprocating periods and air velocities. The accuracy of the 3D model was validated through the comparison of the temperature curves between experimental and numerical data. Results show that the reciprocating cooling and heating systems can reduce the temperature nonuniformity and maximum temperature of cells significantly. For the reciprocating cooling system, it can increase the minimum temperature in cells. The maximum average surface temperature difference curve is a concave parabola that first decreases and then increases with the increase of the reciprocating period. The strategy by increasing the reciprocating period has little influence on lowering the maximum average surface temperature of cells. As for the reciprocating heating system, the reciprocating period has little effect on the variation of temperature for cells when the reciprocating period is higher than 10 s. The temperature difference curve inside of a cell with a different reciprocating period is a parabola too. The maximum average temperature inside of each cell increases with the increase of air velocity, but the increase rate tends to be reduced. For small air velocities, the average temperature inside of each cell increases linearly with the increase of time, but for high air velocities, it increases quadratically.

Oxygen-enriched combustion experiments of individual samples (lignite and semi-char) and their blends were conducted using a thermogravimetric analyzer. The semi-char sample was prepared from Baorixile (BL) lignite under a pyrolysis temperature of 800°C. The differences between semi-char and BL lignite in terms of thermal behaviors and combustion dynamics were investigated. Subsequently, the combustion reactivity corresponding to three ratios of BL lignite to semi-char was analyzed. Results showed that the yield of volatiles from BL lignite was proportional to oxygen concentration below the ignition temperature, whereas that from semi-char was nearly constant. The degree of conversion of semi-char has remained unchanged in each reaction region under different oxygen concentrations. The reduced rate of activation energy of semi-char combustion was larger than that of BL lignite below degree of conversion 0.6. These findings indicated that semi-char can maintain the combustion stability of blends. Further studies found that the thermal interaction between semi-char and lignite resulted in the optimum combustion stability when the proportion of semi-char was from 30 to 50%.

The wide application of combined heat and power (CHP) units increases the interaction between electricity and heating networks and the interest in combined analysis of the integrated electricity and heating networks (IEHNs). However, most of the existing power and mass flow (PMF) analysis methods for IEHNs are deterministic in nature, which cannot address the uncertainties and their effects on the operation of IEHNs. Therefore, the well-known concept of probabilistic power flow (PPF) analysis of an electricity network is extended to IEHNs in this paper. A probabilistic power and mass flow (PPMF) problem of IEHNs considering various uncertainties and correlations in wind speeds, electricity loads, and heat loads under both grid-connected mode and island mode is formulated at first. A probabilistic method based on the Latin hypercube sampling (LHS) technique and Nataf transformation is then developed to solve the PPMF problem. Finally, the effectiveness of the proposed method is verified by a sample IEHN composed of a 33-bus distribution system and a 27-node heating network.

Among various microhydropower plants, gravitational water vortex power plants are emerging because of their simple installation, reduced setup time, and minimal maintenance cost. The methodology and the selection of a suitable basin and turbine blade combinations are yet to be explained by researchers. This study attempts to investigate the parameters that affect the formation and strength of a vortex for efficient power generation using an artificially induced air-core vortex. Computational fluid dynamics based on a two-phase flow analysis of the vortex formation at different basin parameters resulted in the selection of a suitable configuration of the basin. The basin was then used in the blade analysis with different blade shapes at various load conditions. An experimental setup was also fabricated for the validation of the numerical results, in which a close agreement was observed. The proposed methodology could be used to determine the plant specifications and the blade size and shape for various flow rates and heads. The role of vortex height in determining the performance of the gravitational water vortex turbine was explored. Among the four types of blades used in the study, cross-flow blades have shown the best efficiency for the same discharge and head conditions.

Buildings exploit 40% of the total annual global energy consumption and account for 33% of the greenhouse gas (GHG) emissions around the world. A significant portion of this energy is consumed in buildings for heating, cooling, and air-conditioning purposes. Phase change materials (PCMs) can be used as cold accumulators for nighttime ventilation of buildings, also termed the “free-cooling concept.” An experimental test setup was established in the Laboratory for Advanced Energy Materials at US-Pakistan Center for Advanced Studies in Energy (USPCAS-E) for investigating heat transfer during charging and discharging using butyl stearate as PCM for free-cooling application. Effects of airflow rate and different metal additions on PCM charging and discharging were also assessed. Analysis of the data indicated that the increased airflow cuts the PCM charging time but reduces the time for useful cold availability. The addition of metals like aluminum (Al) and copper (Cu) powders to the PCM enhances the heat transfer rate during the charging process by 25 and 15%, respectively. Variation in size of the metal particles reveals that finer the metal size, more it enhances the heat transfer rate of the PCM during the charging process. The results and performance characteristics of the PCM show that it will be suitable for free-cooling applications.

Water injection represents a promising technology to overcome limitations of knock occurrence and fuel enrichment that reduce the efficiency of downsized spark-ignition (SI) engines. This paper presents the results of an experimental investigation performed on a port-fuel injection turbocharged spark-ignition engine within the speed range 3,000–4,500 revolutions per minute (rpm) under medium-high load conditions. Engine tests were carried out by setting the gasoline baseline conditions at 0.9 as the relative air–fuel ratio according to the standard electronic control unit engine map. As the water injection was activated, the fuel amount was steadily reduced to reach the established relative air–fuel ratios (1 and 1.05). A spark timing sweep up to the most advanced one without knock was carried out, and results of engine performance, exhaust gaseous emissions, particle number (PN), and particle-size distribution were measured and compared with the baseline gasoline case. The main findings showed that the water injection was able to stop mixture overfueling and improve fuel efficiency without engine load penalties. Regarding particulate emissions, the higher knock tolerance and better combustion phasing allowed by water injection produced significant reductions in particle number emissions, which were primarily marked at higher engine speeds.

Elevated emission of hydrogen chloride (HCl) from the combustion of biomass in utility boilers is a major issue, as it can cause corrosion, and in combination with the high alkali content often encountered in these fuels, it can deposit molten alkali salts on the boiler’s water tubes. Such deposition can impede the heat transfer and cause further corrosion. Previous work in this laboratory showed that the HCl emissions of biomass combustion can be drastically abated by burning torrefied biomass instead of raw biomass. Alternatively, the present work concentrated on using alkali-based sorbents to capture the HCl emissions from the combustion of raw biomass and reported on their effectiveness. It burned corn straw and corn-based distillers dried grains with solubles (DDGS), both pulverized to the size range 75–150 µm. Their combustion products were treated with calcium carbonate (${\mathrm{CaCO}}_3$), sodium carbonate (${\mathrm{Na}}_2{\mathrm{CO}}_3$), and potassium carbonate (${\mathrm{K}}_2{\mathrm{CO}}_3$). The high-temperature evaluation of the sorbent’s performance was achieved by the coinjection of the sorbents with biomass in a drop tube furnace (DTF) at steady-state steady-flow conditions. Moderate- and low-temperature evaluation of the sorbent’s performance was achieved by allowing the effluents of the batch combustion of the biomass to pass through heated fixed beds of the alkali carbonates. In all experiments, the HCl reductions by the sorbents ranged from 10 to 57% at a molar alkali/chlorine ratio of $\sim 5$ and a gas/sorbent contact time on the order of 1 s. The HCl reduction by the alkali carbonate sorbents at the high temperature (1,350 K) was comparable to that achieved at the moderate temperatures (773 and 573 K), whereas the reduction at room temperature (298 K) was lower. Potassium carbonate was more effective than sodium carbonate, which in turn was more effective than calcium carbonate in the HCl capture. However, under all the current experimental conditions, the replacement of the raw biomass fuel with thermally pretreated biomass (torrefied at 523 K) resulted in HCl emissions that were lower than those from treating the effluents of raw biomass with the previously described alkali carbonate sorbents.

This work examines the effects of diesel fuel oxygenation on the combustion and emissions in a direct injection (DI) diesel engine. This is a predominately computational study, where the influence of the fuel oxygen content at various injection timings and loads is addressed by using an in-house, comprehensive, two-zone model of DI diesel engine combustion, which divides the cylinder contents into a nonburning zone of air and another zone in which fuel is continuously supplied from the injector and burned with entrained air from the air zone. The validity of the model results is assessed favorably against pertinent experimental data, such as cylinder pressure and heat release rate (HRR) diagrams and nitric oxide (NO) and soot emissions generated in this laboratory by conducting tests on an experimental, single-cylinder, DI Hydra (Ricardo/Cussons, Manchester, United Kingdom) diesel engine operated at two different loads and injection timings. Various degrees of oxygenation of conventional diesel fuel and various injection timings were undertaken in the theoretical study at each load. The numerical simulation results provide insight into the local combustion and emissions formation conditions. Numerical modeling determined that cylinder pressures, temperatures, and NO emissions increase, whereas soot emissions decrease with the degree of fuel oxygenation at any load, and also that cylinder pressures, temperatures, and NO emissions decrease, whereas soot emissions increase by retarding the injection timing at any load. These results are used for discussing the implications they have on the behavior of biofuels or diesel fuel blends, where the fuel-bound oxygen and ignition delay (embodied here in the injection timing variable) are the main parameters dictating their behavior. At least for the case of some common biofuels in blends with diesel fuel, it is shown that lower injection timings and higher degrees of biofuel blend oxygenation (inside limiting values) can alleviate the notorious NO–smoke trade-off with respect to a point of lower oxygenation degree lying on a higher injection timing NO–smoke curve (at any constant load).