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This research proposes an H-class micro-mixing gas turbine combustor prototype with a thermal power of 1.15 MW, which employs 40 exterior jet-in-crossflow micro-mixing nozzles with a tapered round outlet to reduce pollutant emissions and prevent the flashback. These nozzles are located by a distribution arrangement in order to improve the temperature distribution uniformity of field flow. To respond to off-design operation of gas turbine, the combustion performance of the micro-mixing combustor prototype is investigated numerically at the rated fuel temperature of 473 K and other ones of 373, 423, 523 and 573 K. The results indicate that NO emission has a relatively high augment as the fuel temperature decreases, which is due to the rising local equivalence ratio. The variation trends of the temperature distribution uniformity, combustion efficiency and total pressure loss are not obvious as the fuel temperature changes. Based on the rated and off-design combustion performance at different radial planes, this research finally proposes an optimal relationship between the axial liner length and micro-mixing nozzle outlet diameter. [Display omitted] • Application of a micro-mixing combustor prototype in an H-class gas turbine. • Combustor employs 40 micro-mixing nozzles with a distribution arrangement. • An exterior jet-in-crossflow nozzle with a tapered round outlet is designed. • Effects of fuel temperature on different combustion performance are investigated. • Optimal relevance between axial liner length and nozzle exit diameter is proposed. [ABSTRACT FROM AUTHOR]

Chemiluminescence is a major spontaneous emission inflame and can be used in combustion diagnostics to evaluate various flame characteristics. OH∗ chemiluminescence is a good indicator for heat release rate analysis in alkane flames. In this paper, a high-resolution ultra-violet imaging system was used to capture the OH∗ chemiluminescence images. The experiments were conducted in a pilot-scale system with a 300 kW combustion chamber. The variety of temperature distribution is evaluated using the outlet temperature distribution factor. The heat release rate dynamic characteristics were discussed by criteria of distribution uniformity on the spatial and temporal dimensions and the characteristic frequency results obtained by three different methods. The result shows that operating conditions with a uniform outlet temperature distribution always have more uniform spatial distribution and smaller temporal fluctuation amplitude of heat release rate. Frequency results obtained by different methods match very well when the heat load ratio is over 70%. The flame frequency characteristics correlate well with the turbulence property compared with the unmixedness of fuel and air. But the oscillation amplitude of heat release is mainly affected by the unmixedness. • MGT part-load performance is limited by flame dynamic characteristics. • Discussion of HRR dynamic characteristics based on chemiluminescence. • Consideration of HRR spatio-temporal distribution property and dynamic characteristic. • Spatio-temporal distribution of temperature can be improved by changing unmixedness. • Flame dynamic characteristics correlate well with turbulence characteristics. [ABSTRACT FROM AUTHOR]

Pumping of self-consolidating concrete (SCC) is a vital construction technique. Curiosities are aroused by the effect of this intense physical process on the hardened properties of SCC. To examine this issue, a total of seven SCC mixtures are pumped at constant flow rates in pipelines with lengths of 324, 600, and 912 m. Parameters related to the hydration stages, air-void system, compressive strength, elastic modulus, and shrinkage at early ages are tested on specimens made of concrete before and after pumping. Results of tested samples find that the spacing factor grows, but the specific surface lessens after pumping. Also, in most cases, the compressive strength and elastic modulus decrease due to the pumping. The variations of these two factors are linearly related to the pumping distance in most cases. Additionally, the variations in the early age of shrinkage cracking show a dependency on the concrete compositions, temperature, and pumping characteristics. [ABSTRACT FROM AUTHOR]

The influence of pumping on the rheological properties of self-consolidating concrete (SCC) is widely recognized, but there is still limited understanding of its behavior within the pipeline. In this study, we propose a novel approach using equilibrium distances to investigate the evolution of rheological properties along the pipeline. Full-scale horizontal pumping circuits spanning 328 m were established to assess the axial development of SCC's rheological properties. Thirteen mixtures, with water-to-cement (w/c) ratios ranging from 0.22 to 0.27, were pumped at discharge rates varying from 5.77 to 12.69 L/s. Our findings show that for pumping setups and material studied, both the w/c ratio of SCC and the discharge rate significantly affected the influence of rheological equilibrium distances on pressure loss gradient changes. In all tested samples, viscosity values required the entire length of the pipeline to reach post-pumping levels, while yield stress values rapidly achieved their fully developed state upon entering the pipeline. Importantly, the predicted pressure loss displayed a strong correlation with experimental measurements, with an accuracy of 89.42% across all tested mixtures. Our predictive model showed an average improvement of 4.6% in accuracy compared to the linear approach, with the most significant enhancement observed in samples with higher w/c ratios. This research sheds new light on the behavior of SCC during pumping and provides valuable insights for optimizing the pumping process. • The equilibrium distance of rheology is introduced to describe SCC flow behavior along the pipeline. • Horizontal pumping circuits spanning 328 m is used. • Factors affecting the equilibrium distance of rheology are discussed. • The prediction accuracy of the model is validated. [ABSTRACT FROM AUTHOR]

The pumping pressure loss of fresh concrete has traditionally been modeled as a linear function of the pumping distance. However, previous studies have suggested that this relationship is nonlinear in nature. This research has identified that the nonlinearity is due to changes in the rheological properties of fresh concrete during pumping. In this study, a new prediction equation has been proposed for the loss of pumping pressure for concrete mixtures with w/c ratios between 0.17 and 0.46, and an equivalent horizontal pipe length between 328 and 912 m. The equation provides a linear approximation of the nonlinear relationship of pumping pressure loss. To account for the effect of rheological changes during pumping, an empirical coefficient related to the initial slump flow of the concrete has been incorporated. The new function can improve the prediction accuracy of pressure loss by 25 % and 4.2 % for horizontal and vertical pumping, respectively. [ABSTRACT FROM AUTHOR]

Exhaust gas recirculation (EGR) is an option proposed to augment the CO 2 content in the exhaust gas for the efficient removal of CO 2. In the field of micro-gas turbine (MGT), EGR is also a feasible solution to improve the part-load performance and fuel flexibility. This research combined EGR with an adjustable fuel feeding combustor to assess the part-load performance of a 300 kW MGT and the flame spatiotemporal characteristics. The radical chemiluminescence intensity of hydroxyl is selected to represent the heat release rate (HRR) in natural gas flames. The influence of EGR on HRR was investigated experimentally under various load ratios (50%–100%) and EGR ratios (0–20%). In addition, the temperature at the combustion chamber outlet is also measured. The results show that EGR can effectively reduce OTDF when the load ratio is high. Both the spatial distribution non-uniformity and fluctuation amplitude of HRR are suppressed after applying EGR. And EGR can also reduce the influence of mixing on HRR spatiotemporal characteristics. At last, the frequency characteristics of HRR are analyzed. The result shows that the flame frequency has a strong correlation with the characteristic frequency of turbulence. • EGR has an important impact on MGT performance, especially for off-design conditions. • The change of heat release rate characteristic can directly reflect the impact of EGR. • Consideration of HRR spatio-temporal distribution property and dynamic characteristic. • EGR can improve part-load performance and slightly increase characteristic frequency. • MGT can directly apply EGR without structural optimization. [ABSTRACT FROM AUTHOR]

Pumping is a widely used placement means for concrete construction, but both fresh and hardened property changes in concrete due to pumping. In this review, the effects of pumping on both the fresh and hardened properties of various concrete mixtures are presented in terms of each specific characteristic. Analyses of data from the published literature showed that the air content of fresh concrete is altered after pumping. The general trend in the change in rheological properties of fresh concrete due to pumping was also determined, and the mechanisms of this trend were discussed. Moreover, the improvement in the compressive strength of hardened concrete was investigated, which is considered to result from the pumping-induced hydration acceleration and the air content variation. Finally, changes in the durability of hardened concrete were discussed, and future research topics were suggested. [ABSTRACT FROM AUTHOR]

Pumping changes the rheological properties, workability and construction performance of fresh concrete. However, there were limited knowledges on influences of discharge rates and pumping distances on the fresh properties of concrete. In this paper, effects of various discharge rates and pipeline lengths on rheological properties of self-consolidating concrete (SCC) after pumping were studied. A total of 12 SCC mixtures with the slump flow of 650–745 mm were pumped in pipelines with measured lengths of 342 m, 545 m, and 1044 m by constant discharge rates ranging between 5.1 and 11.4 L/s. Rheological properties were measured before and after pumping. Physical conditions of SCC during pumping, including pressure, shear, and temperature were estimated theoretically and experimentally. Moreover, the total organic carbon in the pore solution of SCC mixtures was measured to evaluate the change of superplasticizer adsorptions after pumping. Test results indicated that, due to pumping, the yield stress increased; the initial tangential viscosity decreased and the shear-thickening phenomenon was eliminated. The changes of yield stresses and viscosity were encouraged by discharge rates. Besides, lower initial slump flow of SCC exhibited a larger slump flow loss after pumping due to a higher shear rate experienced during pumping. The yield stress and viscosity after pumping increased with the increase of pipeline length at similar discharge rates, but decreased with the pipeline length under similar pumping pressures. The adsorption of superplasticizer increased after pumped at relative low discharge rates (5.2–5.7 L/s), but decreased at discharge rates of 7.7–10.8 L/s. [ABSTRACT FROM AUTHOR]

• Resistivity evolution of fresh HSC were measured to characterize the early age hydration process in HSC. • Influence of pumping on early age hydration in HSC were evaluated. • Changes in dynamic yield stress of HSC after pumping were related to corresponding changes in hydration process. The pumping process exerts high pressure and strong shearing on fresh concrete, which may affect the hydration process and rheological behavior of concrete. In this paper, full-scale pumping circuits with lengths of 348-, 600-, and 924-m were established to evaluate the effect of pumping on hydration and rheology of concrete. Electrical resistivity measurement was employed to indirectly evaluate the hydration process of concrete. Ten high-strength concrete (HSC) mixtures with slump flow of 680 ± 50 mm and strength grades of C60-C100 were pumped, and HSC mixtures were sampled before and after pumping for rheological properties and electrical resistivity measurements. Findings indicated that the hydration process, determined by the electrical resistivity evolution, was accelerated after pumping. The end of the dormant period of fresh concrete was decreased by 10.3%-27.3%, and the end of the setting period was shortened by 15.6%-28.4% after pumping. The reduction in the dormant period can be well correlated with the drop in slump flow or increase in dynamic yield stress after pumping. [ABSTRACT FROM AUTHOR]

• Changes in rheological properties of high-strength concrete due to pumping were systemically investigated. • Fresh concrete was sampled in dismantled pipes for the rheological test. • Shear-thickening in high-strength concrete was eliminated after pumping. • Shearing energy during agitation and pumping was estimated and correlated to the changes in viscosity. Pumping of high-strength concrete (HSC) in high-rise or long-span structures is of paramount importance in constructions. However, pumping technology in practice is highly dependent on practical field experience, and full-scale testing that is carried out for complex projects involving new materials or long pumping distances. In this paper, a long pumping circuit was built to study changes in fresh properties of HSC due to pumping. In total, 10 HSC mixtures with strength grades of C60 to C100 were pumped at constant flow rates in pipelines measuring 348, 600 and 924 m in length. Rheological properties, workability characteristics, and concrete temperature were measured on concrete specimens sampled before and after pumping. Rheological properties of concrete sampled in dismantled pipes shortly after the end of pumping were also determined. Test results indicated that the yield stress increased, the initial tangential viscosity decreased and the shear-thickening phenomenon was eliminated due to pumping. The increase in yield stress mostly occurred in the first half of the pipeline, and the tangential viscosity decreased nearly linearly along the pipe length. The levels of drop in initial tangential viscosity were found to positively correspond to the calculated shearing energy, which is estimated given the shear rate, apparent viscosity and elapsed time during agitation and pumping. [ABSTRACT FROM AUTHOR]

The combustion characteristics of ignition processes under different ignition fuel ratios were studied on a natural gas-fueled micro gas turbine combustion chamber. With the changing of air mass flow, the equivalence ratio varied from 0.024 to 0.994 at which the fuel mass flow remained the same. The flue gas compositions were measured at the combustion chamber outlet, and used to calculate the combustion efficiency. To characterize the relative flame stability, optical measurements and digital image processing techniques were applied. The results indicate that the combustor can ignite successfully under the ignition fuel ratio conditions of 10%, 15%, and 20%, in which the corresponding equivalence ratios are 0.082–0.497, 0.082–0.746, and 0.098–0.994, respectively. Moreover, the combustion efficiency decreased with the descending equivalence ratio. However, the amount of CO and unburned CH 4 in the combustion products increased as the equivalence ratio decreased. The heat release rate in the reaction zone and the morphological characteristics of the flame were obtained using the gray level of average flame images. Furthermore, the flame fluctuation was analyzed by coefficient of variation of the flame area, and the relative flame stability was analyzed by the probability distribution density of the relative flame area ratio. The appropriate equivalence ratios for ignition are around 0.245, 0.243–0.369, and 0.196–0.326 under the ignition fuel ratio conditions of 10%, 15%, and 20%. The ignition fuel ratio has considerable influence on combustion efficiency, combustion product, and flame stability. • Experiments of ignition process of a 300 kW micro gas turbine. • Development of an flame analysis method based on high speed observable light imaging. • Consideration of combustion efficiency and relative flame stability in selection. • Big difference in the relative stability with different ignition operating conditions. • The results show the proposed method can successfully capture the flame fluctuations. [ABSTRACT FROM AUTHOR]

Abstract Because of the environmental, technical and economic benefits, plant-based (e.g. jute) natural and mineral-based (e.g. basalt) natural fiber reinforced polymer (FRP) composites are considered as alternatives for conventional glass FRP composites. However, the scarcity of data on the long-term durability of natural FRP composites becomes a major barrier for their wider use in different engineering areas. In this work, durability studies were performed to evaluate the effects of water and alkali solutions, and the temperature of their solutions on weight gain, tensile properties and surface morphology of jute and basalt fabric reinforced epoxy composites. In total, four types of composite specimens (i.e. untreated jute fabric/epoxy, alkali-treated jute fabric/epoxy, silane-treated jute fabric/epoxy and untreated basalt fiber/epoxy) were fabricated and exposed to different ageing conditions for 180 days. The water absorption and tensile properties of these four composite specimens were measured and compared. The results showed that in general, the weight gains of the three plant-based natural jute/epoxy specimens (i.e. from 5.0% to 8.5%) were larger than that of the mineral-based natural basalt/epoxy composite (i.e. from 1.1% to 2.2%). Both alkali and silane treatments of jute fiber reduced the water absorption and enhanced the tensile strength of the resulting jute fabric/epoxy composites. For all the four types of composites, increasing exposure temperature of the water and the alkali solutions caused the reduction in their tensile strength. The strength reduction of these four types of composites at alkali solution was larger than the reduction of the corresponding composite at the water solution. In addition, their reduction in tensile strength was more pronounced compared with that in their Young's modulus. Compared with mineral-based basalt/epoxy composites, the untreated, alkali-treated and the silane-treated plant-based jute fabric/epoxy composites showed higher tensile strength reduction retention for the considered ageing conditions. However, the basalt fiber composites had much higher modulus retention. The deterioration of the interfacial properties of these composites at different ageing conditions was confirmed by the SEM observations. [ABSTRACT FROM AUTHOR]

Hydrogen has been regarded as an important alternative fuel, especially in gas turbine applications. However, the premixed combustion of pure hydrogen has problems such as easily flashback and high NO x emissions. A more reasonable method of combustion is to use micro-mixing technology combined with water vapor dilution. This work experimentally investigated the influences of dilution rate (D) and equivalence ratio (φ) on the flame characteristics of hydrogen-air micro-mixing combustion diluted with water vapor. Results show that increasing D reduces the flame area by reducing the downstream OH radical signal, which is contrary to the effect of CO 2 dilution. The flame local curvature radius shows that the micro-mixing combustion is a high turbulence intensity combustion, and the convex structure is more frequent. Moreover, increasing φ or decreasing D leads to a decrease in the instantaneous average curvature radius (R ave), indicating more small-scale wrinkle structures are generated. D and φ have a similar influence on the fluctuations of R ave and flame area in the time domain, while the fluctuation of the flame area is more evident near the lean-burn limit. When D = 25%, the frequency characteristics of the flame structure and chemical reactions are synchronized. [ABSTRACT FROM AUTHOR]

UHPC is a cement-based material characterized by outstanding strength and durability, but its high viscosity poses challenges for field application. Herein, we built a Horsfield theory modified cementitious packing structure by utilizing fly ash microsphere (FAM), aiming to release water, thus, reduce viscosity. The wet packing density indicated that FAM could optimize the packing structure, and transform locked water into free water. Meanwhile, 1H NMR revealed the variation of adsorbed water to free water due to the surface characteristics of FAM. Consequently, more free water could be obtained, which thereby reduced the viscosity up to 75 %. The slump flow, t500, v-funnel flow time and J-ring tests were further conducted to assess the workability, where the results indicated the modified UHPC met the standards for self-compacting concrete. Besides, the synergistic water-reducing strategy attributed to cementitious materials packing optimization can maintain a low w/b (<0.2), which contributes to an ultrahigh strength of 120.5 MPa, realizing the feasibility of developing self-compacting UHPC This study provides a new approach to enhance the workability of UHPC without sacrificing mechanical property and durability, expanding the field application of UHPC. [Display omitted] [ABSTRACT FROM AUTHOR]

To respond to off-design operation of the micro-gas turbines, this research proposed an adjustable fuel feeding combustor (AFFC). The AFFC employed a main fuel distribution device and an active control method called the adjustable fuel feeding method (AFFM). Through the main fuel distribution device, the AFFC can switch various groups of working main fuel tubes (MFTs), ultimately achieving the AFFM. Each group has a different symmetrical distribution feature of working MFTs. Based on these features, the AFFM characteristic number ( U ) has a unique calculation value for the AFFM at each group, and particularly, it was entirely different from the values of U for the AFFM at the other groups. In this research, four different working MFT groups were presented, and the values of U were calculated to be 0.143, 0.333, 0.429 and 1 for the AFFM at each group, respectively. As U changes, the AFFC combustion performance was investigated numerically at various combustor inlet air temperatures ( T 3 ) of 600, 700, 800, 900 and 1000 K. Moreover, the CFD method applicability was verified by the experimental data. The results indicate that at different T 3 , NO emission has various trends with the rising U due to the coupling influences of the fuel flow and fuel jet velocity of each working MFT, while CO emission and combustion efficiency are only affected by the AFFM at the low T 3 of 600 K. The outlet temperature distribution factor keeps growing, and the total pressure recover factor remains almost the same as U rises. [ABSTRACT FROM AUTHOR]