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Light is often considered the primary factor leading to the regeneration failure of Korean pines (Pinus koraiensis) under the forest canopy. However, studies on the effect of light on Korean pines mainly focus on the use of an artificial sunshade net to control shade; field studies on the canopy are extremely scarce, and the current experimental results are contradictory. For a deeper understanding of the relationship between light conditions and understory Korean pine trees, the conditions of low, middle, high and full light (control) under the forest were tested at 18 years of age. The photosynthetic pigments, chlorophyll fluorescence, non-structural carbohydrate metabolism, antioxidant enzyme activity, and nutrient concentrations of current-year needles from Korean pine trees were measured. From June to September, light intensity and quality decreased under full light, but following leaf fall, understory light conditions improved slightly. As the light conditions improved, the photosynthetic pigments in the needles decreased, but Car/Chl were highest in the needles under full light. All light conditions had a positive correlation with glucose concentrations and Rubisco activity. Full-light needles had the highest APX activity, DPPH scavenging capacity, and proline concentration, as well as higher NPQ and lower Fv/Fm readings. This indicated that full-light Korean pine trees were stressed and inhibited photosynthesis to some extent, while the understory light environment may alleviate stress. The conservative strategy of storing more starch and using less glucose in understory Korean pine trees may be one of the reasons for the observed differences in growth rates among Korean pine trees under varying light conditions. Overall, this study implies that understory light during the growing season is not always unfavorable to 18-year-old Korean pine trees; this means that 18-year-old Korean pine trees still have shade tolerance to some extent and are capable of living under a canopy of deciduous trees.

A new type of flame organization, dual-stage lean premixed (DLP) combustion, is proposed. It constructs lean premixed flame with nonuniform equivalence ratio in the combustion zone, which is aimed ...

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.

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 CH4 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.

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.

To improve off-design operation performance of micro-gas turbine, we proposed an adjustable fuel feeding combustor (AFFC), and it employed the lean premixed swirling combustion technology and the adjustable fuel feeding method (AFFM). The AFFM was achieved by switching the various working groups of main fuel tube, and represented by its unique characteristic number (U). To verify the availability of adopted models, the AFFC combustion performance was investigated numerically at different equivalence ratios (ϕ) in ANSYS CFX. The results indicate that NO emission has various trends with the rising U under different ϕ due to the coupling influence of fuel flow and jet velocity in each working main fuel tube. Although the AFFM has almost no effect on the distribution of outlet temperature and the length of primary recirculation zone, the maximum and non-uniform coefficient of outlet temperature increase with the rising U.

Premixed flames have shown different behaviors while operating with inhomogeneous equivalence ratio. This property can be used to improve the performance of premixed flames. Present work proposed the idea of dual-stage lean premixed (DLP) combustion, which constructs lean premixed flames with equivalence ratio staged radially. Laminar DLP flames were built in a coaxial jet burner. The combustion and NOx emission characteristics of DLP flames were analyzed and compared to the homogeneous cases. Results showed the arrangement of DLP combustion allows more heat to support the ignition of secondary premixed gas, which is located in periphery and has a lower equivalence ratio. So, the DLP flames can reach a fairly low global equivalence ratio compared to homogeneous cases. Besides, the secondary flame can produce a certain number of intermediate products during combustion, which will reduce NOx into N2, helping limit the NOx emissions of the overall combustion. In short, the idea of DLP combustion may provide new thinking for the development of clean combustion.