Multi-stage injection with pilot injection and post injection has been widely used for the noise and emissions reduction of diesel engines. Considering many parameters to be decided for optimal combustion, computer simulations such as three dimensional computational fluid dynamics (3D-CFD) and lower dimensional codes should play a role for optimal selection of intervals and quantity ratios. However, the data for the sprays are insufficient for reproducing the actual fuel-air mixture formation process related to pilot and post injection. Hence, there is a need for experimental data with a small-quantity injection. The small-quantity injection is characterized with an injection rate shape similar to a triangle rather than a rectangle. This study is mainly focused on the spray characteristics of diesel sprays in which the entire process is dominated by unsteady injection processes. The effects of injection parameters and nozzle hole diameter on spray penetration, spray angle, and fuel concentration are studied with the help of a rapid compression and expansion machine. A hybrid of shadowgraph and Mie scattering imaging setup is used to visualize both spray liquid phase and vapor phase at the same time. A highspeed camera with a frame rate of 90,000 fps is used to acquire spray images. Two injectors with a nozzle hole diameter of 0.12 mm and 0.14 mm are used. The studies are performed at the injection pressure of 40, 80, and 120 MPa while environmental temperature of 850 K. The experimental results show that the development of the spray tip is proportional to t and then to t 1/2 at the later stage, and after the end of the injection, the spray tip penetration is found to follow t 1/4. Also, the spray liquid penetration, spray dispersion, and air-fuel mixing processes are evaluated and compared with various injection parameters. In addition, the instantaneous behavior of the near-nozzle spray angle is studied carefully in order to provide reliable input data for spray models.
This study aims to utilize high-pressure split-main injection for improving the thermal efficiency of diesel engines. A series of experiments was conducted using a single-cylinder diesel engine under conditions of an engine speed of 2,250 rpm and a gross indicated mean effective pressure of 1.43 MPa. The injection pressure was varied in the range of 160-270 MPa. Split-main injection was applied to reduce cooling loss under the condition of high injection pressure, and the split ratio and the number of injection stages were varied. The dwell of the split main injection was set to near-zero in order to minimize the elongation of the total injection duration. As a result, thermal efficiency was improved owing to the combined increase in injection pressure, advanced injection timing, and split-main injection. According to the analysis of heat balance, a larger amount of the second part of the main injection decreased the cooling loss and increased the exhaust loss. Computational fluid dynamics calculations were performed to reveal the causes of the lower cooling loss; however, the results could not capture the experimental trend when using an ordinary spray cone angle. While using a wider spray angle for the second part of main injection, the calculated trend improved. The total cooling loss depends on the balance between the cooling losses by the first and second main sprays.
BACKGROUND: Woody biomass has a low hydrothermal-carbonization (HTC) degree and the hydrolysis process of some of its components is similar to that of saccharides. To improve the adsorption performance of wood-chips hydrothermal char (hydrochar) for tetracycline in water, molasses and potassium ferrate (K 2 FeO 4 ) were added to its HTC process; K 2 FeO 4 catalyzed the carbonization of raw materials and the surface of wood chips and saccharides in molasses, along with the iron ions mutually polymerized, added more reactive-oxygen functional groups to the hydrochar surface. The effects of K 2 FeO 4 and molasses on the morphology, pore structure, surface oxygen-containing functional groups, and tetracycline-adsorption properties of hydrothermal carbon were investigated. RESULTS:The strong oxidizing properties of K 2 FeO 4 promoted the hydrolysis of raw material. The modified hydrochar formed more oxygen-containing functional groups and produced Fe O bonds with an increased specific surface area. For the adsorption of tetracycline in water, the pseudo-second-order kinetic model and Freundlich isotherm were more consistent with the hydrochar-adsorption process. The adsorption mechanism favored a combination of physical and chemical adsorption, with chemisorption being predominant. The maximum tetracycline-adsorption capacity of HTC-0.15Fe was 119.7 mg g −1 , which is significantly higher than that of unmodified hydrochar HTC-C (56.4 mg g −1 ). Furthermore, molasses addition effectively improved the hydrochar structure, forming carbon-coated iron-core particles on its surface, which increased adsorption performance.CONCLUSION: K 2 FeO 4 -catalyzed hydrochar produced from wood chips and sugarcane molasses is an effective adsorbent for tetracycline removal from water. This work provides innovative insights into the recycling and effective use of wood chips and molasses for environmental remediation and waste treatment.
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