Search Results (14)

Taking into account the approaches to ecology and social policy, the development of technologies for optimizing the combustion process for thermal power plants, one of the key sources of greenhouse gas emissions, is relevant. This article analyzes approaches that improve the combustion process efficiency in thermal power plants, as well as speed up the development of various operating modes. Particular attention is paid to the control of fuel composition and geometric parameters of a burner device. Optimal settings of these parameters can significantly impact the reduction in harmful emissions into the atmosphere, though finding such parameters is a labor-intensive process and requires the use of modern automation and data processing tools. Nowadays, the main methods to analyze and optimize various characteristics are machine learning methods based on artificial neural networks (ANNs), which are used in this work. These methods also demonstrate the efficiency in combination with the optimization method. Thus, the use of approaches based on the combustion process optimization can significantly improve the environmental footprint of thermal power plants, which meets modern environmental requirements. The obtained results show that the most significant effect on the $N{O}_X$ content has the mass flow rate change of primary air and fuel with a change in geometric parameters. The decrease in $N{O}_X$ concentration in comparison with the calculation results with basic values is about 15%. Full article

In order to explore the influence of pilot structure on the lean ignition characteristics in a certain type of internally staged combustor, the current study was conducted on the effects of the auxiliary fuel nozzle diameter, the rotating direction of the pilot swirler, and the swirl number on the lean ignition fuel–gas ratio limit, combining numerical simulation and experimental validation. The optimization potential of the mixing structure of this type of internally staged combustor was further explored. It indicated that the lean ignition fuel–gas ratio limit was significantly influenced by the diameter of the auxiliary fuel nozzles the swirl number of the pilot swirler and the combination of the same rotating direction for both pilot swirlers, while the mass flow rate of air was constant. Increasing the diameter of the auxiliary fuel path nozzles (0.4~0.6 mm) and having excessively higher or lower swirl numbers of the pilot module primary swirlers are not conducive to broadening the lean ignition boundary. Compared with the two-stage pilot swirler with the same rotation combination, the fuel–gas ignition performance of the two-stage pilot swirler with the opposite rotation combination is better. Under the typical working conditions (the air mass flow rate is 46.7 g/s and the ignition energy is 4 J), for a pilot swirler with a rotating direction opposite to the main swirler, the diameter of the auxiliary fuel nozzles is 0.2 mm, the swirl number of first-stage of pilot swirler is 1.4, and the lean ignition fuel–air ratio was reduced to 0.0121, which is 32.78% lower than the baseline scheme, which further broadens the lean ignition boundary of the centrally staged combustion chamber. Full article

The term “sea effect” generally refers to the process of air mass modification after cold air flows above a warm sea surface. Affected by the sea effect, small-scale and sudden fogs have occasionally been observed on the western coast of the Bohai Sea. A more in-depth study of this type of fog is crucial for ensuring the safety of maritime and aerial traffic routes in this region. This study investigated the formation mechanism of this specific type of fog on the morning of 17 October 2007, utilizing both meteorological stations and 255 m tower observations, combined with the results of the Weather Research and Forecasting model (WRF). It is demonstrated that Bohai Sea evaporation and the associated water vapor advection played crucial roles in the formation of fog along the west coast of the Bohai Sea. The cold return flow became more moist as it passed over the warm Bohai Sea, which was the primary contributor to triggering regional fog on the western coast. A moisture budget analysis revealed that water vapor from the Bohai Sea intruded into its western coast along an eastward trajectory, dominating the oscillations in the net moisture flux. The eastern water vapor flux significantly increased at 17:00 on the 16th (Local time, LST), reaching its peak at 21:00. Correspondingly, the fog water growth rate began to increase at 23:00 on the 16th, reaching its maximum at 03:00 on the 17th. A sensitivity experiment on evaporation further indicated that the Bohai sea effect played a decisive role in fog formation. With a tenfold reduction in evaporation from the Bohai Sea and subsequent significant weakening of water vapor advection, the simulated fog along the western coast of the Bohai Sea completely disappeared. Understanding the formation mechanism of this type of fog is beneficial for refining forecasting focal points, thereby enhancing forecast accuracy in a targeted manner. Full article

The auto industry aims to deliver cost-effective, efficient vehicles to meet customer needs. They are utilizing aluminum to lower expenses, enhance durability, and lighten vehicles. Currently, the industry is developing a high-speed blow forming (HSBF) technique—a faster version of the aluminum thermoforming process, superplastic forming (SPF). HSBF allows the rapid creation of aluminum bodywork or structural parts at high temperatures using pressurized gas. It can produce up to 25 parts per hour, significantly faster than SPF, which only produces 4 parts per hour. The primary objective of this project is to select and characterize a seal that can increase the production rate to 120 parts per hour by allowing the sheet to flow into the mold, especially during the initial stages of the forming process, where most of the deformation occurs. Several test benches were developed to assess the performance and durability of the selected high-temperature seals under conditions that imitate the HSBF process. During the tests, low air pressures are applied to a gasket-enclosed cavity and the resulting mass-flow leakage is measured. The temperature of the mold is kept constant at approximately the superplastic temperature of the aluminum alloy. Through testing, we derived leakage mass flow curves based on cycle count, showcasing the superior sealing ability and longevity of packing seals in HSBF conditions. The seals displayed good durability and sealing performance under HSBF operational conditions, sustaining over 3000 cycles. Moreover, the seals attained a leakage mass flow rate of around 0.3 g/s·m·bar, nearly ten times below the target application limit of 2 g/s·m·bar, confirming their superior performance. Full article

This study presents the implementation of a micro-generation system and its operation procedure, based on a dual fuel diesel engine using natural gas as the primary fuel and conventional diesel as the pilot fuel. On the other hand, the evaluation and validation results by experimental testing of a model according to International Energy Agency—IEA—Annex 42, applied to dual fuel diesel micro-cogeneration system, are also presented. The control procedure for experimental operation depends of both inputs’ electric power generation demand and desired substitution level due a given natural gas availability. The heat recovery system of the micro-generation system uses a gas–liquid compact heat exchanger that was selected and implemented, where wasted heat from exhaust gases was transferred to liquid water as a cool fluid. Effective operation engine performance was determined by measurement of masses’ flow rate such as inlet air, diesel and natural gas, and also operation parameters such as electric power generation and recovered thermal power were measured. Electric power was generated by using an electric generator and then dissipated as heat by using an electric resistors bank with a dissipation capacity of $18\mathrm{kW}$. Natural gas fuel was supplied and measured by using a sonic nozzle flowmeter; in addition, natural gas composition was close to $84.7\%$ ${\mathrm{CH}}_4$, $0.74\%$ ${\mathrm{CO}}_2$ and $1.58\%$ ${\mathrm{N}}_2$, with the rest of them as higher hydrocarbons. The highest overall efficiency (electric efficiency plus heat recovery efficiency) was $52.3\%$ at $14.4$ kW of electric power generation and $0\%$ of substitution level. Several substitution levels were tested at each engine electric power generation, obtaining the maximum substitution level of $61\%$ at $17.7$ kW of electric power generation. Finally, model prediction results were closed to experimental results, both stationary and transient. The maximum error presented was close to $20\%$ associated to thermal efficiency. However, errors for all other variables were lower than $10\%$ for most of micro-cogeneration system operation points. Full article

Recently, radiation-absorbing phase change material (PCM) for thermal storage that can discharge thermal energy on demand when no radiation is present has been developed and tested indoors. Organic materials with limited thermal conductivity slow down the thermal response processes when charging and discharging. For various industrial applications, much research is devoted to the introduction of solar collectors with the best possible integration of solar thermal collector and PCM in terms of both shape and material. In this study, the performance of a solar collector is examined in relation to the additive effects of aluminum particles in spherical capsules. For the transfer fluid temperature with the behavior of the heat storage, a mathematical model of the solar collector was created. The integrated system consists of two primary steps: a first phase that involves an isolated duct covered in glass, and a second step that involves an array of spherical capsules used as storage. The solar air collector is 1.32 m in width and 2.450 m in length. The PCM unit has a 7.7 cm diameter, 0.15 cm thickness, and is filled with a paraffin wax with concentrations between 0.1 and 0.5 weight of nanoparticle aluminum powder. The air mass flow rate varies from 0.03 kg/s up to 0.09 kg/s, while the temperature varied from 30 to 35 °C. The results obtained from experiments agreed with the predicted results. The reduction in charging time was approximately 70% as the cooling rate increased. The improvement of efficiency of thermal storage reached 76.8% and 71%, at mass flow rates 0.07 kg/s and 0.05 kg/s for pure paraffin wax. The overall thermal storage performance for the system was enhanced from 21.7% to 78.9%. Full article

This article discusses the atomization of composite liquid fuels. A large group of injectors is considered. A comparative analysis of the atomization characteristics (droplet sizes and velocities, jet opening angles) and the influence of the fuel characteristics (density, viscosity, component composition) and the process parameters (the ratio of the fuel–air mass flow rates, the features of the jet formation) has been carried out. Finally, the most effective types of injectors, which provide for the necessary characteristics of fuel atomization for its combustion, have been determined. The most favorable conditions for the applicability of each type of atomization have been formulated. Possible mechanisms of secondary fragmentation of droplets of composite fuels have been analyzed: those resulting from mutual collisions of droplets in the flux and from the interaction with a solid surface as well as those resulting from thermal overheating in the presence of a phase boundary or a large gradient of component volatility. A conclusion is made about the need of using a synergistic effect of primary and secondary atomization of fuel suspension droplets. Full article

This paper investigated the effect of air leaking into the working fluid on the performance of a steam ejector. A simulation of the mixing of air into the primary and secondary fluids was performed using CFD. The effects of air with a 0, 0.1, 0.3 and 0.5 mass fraction on the entrainment ratio and internal flow structure of the steam ejector were studied, and the coefficient distortion rates for the entrainment ratios under these air mass fractions were calculated. The results demonstrated that the air modified the physical parameters of the working fluid, which is the main reason for changes in the entrainment ratio and internal flow structure. The calculation of the coefficient distortion rate of the entrainment ratio illustrated that the air in the primary fluid has a more significant impact on the change in the entrainment ratio than that in the secondary fluid under the same air mass fraction. Therefore, the air mass fraction in the working fluid must be minimized to acquire a precise entrainment ratio. Furthermore, this paper provided a method of inspecting air leakage in the experimental steam ejector refrigeration system. Full article

An indirect evaporative cooling system combining with thermoelectric cooling technology (i.e., TIEC system) is proposed, in which a counter-flow plate-fin indirect evaporative cooler is inserted with thermoelectric cooling (i.e., TEC) modules. In hot and humid climate, condensation may occur on the dry channel surface of the cooler. For the TIEC system, with the aid of TEC technology, the surface temperature of the dry channel can be much lower than that of a traditional indirect evaporative cooler, thus, the condensation from the primary air is more likely to take place. A numerical model of this novel TIEC system is developed with specifically taking condensation from primary air into account. Detailed performance analysis of the TIEC system is carried out. Analytical results found that the condensation from primary air reduces the dew point effectiveness by up to 45.0% by weakening the sensible heat transfer but increases the coefficient of performance by up to 62.2% by increasing the latent heat transfer, under given conditions. The effects of main operating conditions, such as the electrical current I and number n of TEC modules, inlet temperature T_p,i, humidity ratio RH_p and velocity V_p of the primary air, and the mass flow rate ratio x of secondary to primary air, are investigated under non-condensation and condensation states. It is shown that condensate is more easily produced under higher I, n, T_p,i, RH_p, x and lower V_p. Full article

It is of practical significance to understand the flame puffing behavior under varying mass flow rate of primary air ṁ_pri. An experiment was conducted to study the impact of ṁ_pri on flame puffing in a swirl partially premixed combustor, the puffing behavior of six significant flame properties was examined. The results showed that almost every spectrum had two fundamental frequencies, which is different from the single-peak spectrum of non-swirl flame. The flame heat-release rate, flame area, and flame equivalent width had identical dominant frequency and sub-dominant frequency, both decreased with the increasing of ṁ_pri. It was attributed to the decreased overall flame temperature caused by the improved mixing of fuel and primary air. All measured frequencies were in the range of 3–14 Hz, but the predicted frequencies from the theoretical models based on non-swirl flame were larger than the measured. This indicates the puffing frequency of swirl flame was much more sensitive to the variation in ṁ_pri than the frequency of non-swirl flame. Moreover, the amplitude of flame length was the smallest in all properties, with the most weakened oscillating intensity. While the amplitude of the flame area and flame equivalent width were the largest, with the strongest oscillation level. Consequently, the flame puffing is mainly attributed to the oscillation in width direction. Full article

Flame pulsation has a significant effect on combustion, and understanding its oscillatory behavior is important to the combustion community. An experiment was performed to analyze the pulsation characteristics of a swirl non-premixed flame under various parameters. The results showed that as fuel mass flow rate increased, the puffing frequency increased due to the decreased flame radiation fraction, and the puffing amplitude became smaller resulting in a more stable flame. With an increase in combustor pressure, the flickering frequency declined because of the increasing soot radiation, while the flickering amplitude uniformly increased, leading to more deteriorative flame stability. With an increment in mass flow rate of primary air, the puffing frequency decreased due to the enhanced mixing between fuel and primary air. Also, the puffing amplitude had an oscillating relationship with the mass flow rate of primary air. When the exit velocity of the injector was increased, the flickering frequency diminished nearly linearly because of the improving swirl intensity, and the flickering amplitude was approximately unaffected by injector exit velocity. Moreover, the measured puffing frequencies summarized over all cases varied within the range of 3–22 Hz, the predicted values from theoretical models based on non-swirl flame also fell within this range. The puffing frequency of swirl combustion was more sensitive to the variation in operating conditions than that of non-swirl combustion. Additionally, the obtained correlations indicated that the Strouhal number St was proportional to Fr^−1.4 (the Froude number) and Re^−2.9 (the Reynolds number), respectively. Full article

Flame shape and size for a high-pressure turbulent non-premixed swirl combustion were experimentally investigated over a wide range of varying parameters including fuel mass flow rate, combustor pressure, primary-air mass flow rate, and nozzle exit velocity. A CFD simulation was conducted to predict the flame profile. Meanwhile, a theoretical calculation was also performed to estimate flame length. It was observed that flame length increased linearly with increasing fuel mass flow rate but decreased with the increment of combustor pressure in the power function. The flame diminished at a larger primary-air mass flow rate but remained unaffected by the increasing nozzle exit velocity. Considering the global effect of all parameters at a particular pressure, the flame length generally decreased as the primary-air to fuel ratio increased. This was attributed to the reduced air entrainment required to dilute the fuel to stoichiometric proportions. The CFD simulation offered a good prediction of the variation trends of flame length, although some deviations from experimental values were observed. The theoretical calculation estimated the trends of flame length variation particularly well. Nevertheless the difference between the theoretical and experimental results was found to be due to the swirl influence. Hence, a swirl factor was proposed to be added to the original equation for swirl flames. Full article

Steam-diluted combustion in gas turbine systems is an effective approach to control pollutant emissions and improve the gas turbine efficiency. The primary purpose of the present research is to analyze the influence of steam dilution on the combustion stability, flame structures, and CO emissions of a swirl-stabilized gas turbine model combustor under atmospheric pressure conditions. The premixed methane/air/steam flame was investigated with three preheating temperatures (384 K/434 K/484 K) and the equivalence ratio was varied from stoichiometric conditions to the flammability limits where the flame was physically blown out from the combustor. In order to represent the steam dilution intensity, the steam fraction Ω defined as the steam to air mass flow rate ratio was used in this work. Exhaust gases were sampled with a water-cooled emission probe which was mounted at the combustor exit. A 120 mm length quartz liner was used which enabled the flame visualization and optical measurement. Time-averaged CH chemiluminescence imaging was conducted to characterize the flame location and it was further analyzed with the inverse Abel transform method. Chemical kinetics calculation was conducted to support and analyze the experimental results. It was found that the LBO (lean blowout) limits were increased with steam fraction. CH chemiluminescence imaging showed that with a high steam fraction, the flame length was elongated, but the flame structure was not altered. CO emissions were mapped as a function of the steam fraction, inlet air temperature, and equivalence ratios. Stable combustion with low CO emission can be achieved with an appropriate steam fraction operation range. Full article

Air high in humidity leads to uncomfortable conditions and promotes the growth of different fungi and bacteria, which may cause health problems. The control of moisture content in the air using traditional air conditioning techniques is not a suitable option due to large consumption of primary energy and hence emission of greenhouse gases. The evaporative cooling technology is a cost effective and eco-friendly alternative but can provide thermal comfort conditions only under low humidity conditions. However, the evaporative cooling method can be used effectively in conjunction with desiccant dehumidifiers for better control of humidity. Such systems can control the temperature and humidity of the air independently and can effectively utilize the low-grade thermal energy resources. In this paper, the theoretical analysis of desiccant based evaporative cooling systems is carried out for five cities in Saudi Arabia (Jeddah, Jazan, Riyadh, Hail, and Dhahran). It has been observed that the coefficient of performance (COP) of the system varies from 0.275 to 0.476 for different locations. The water removal capacity of the desiccant wheel is at its maximum for the climatic conditions of Jazan and at its minimum for Hail. The effect of climatic conditions of five cities on regeneration temperature, air mass flow rate, and potential of solar energy has been evaluated using RET Screen software. Full article