Flow directed spark stretch and flame propagation in a high-tumble production engine

This study performs endoscopic high-speed imaging to enhance the fundamental knowledge of in-cylinder flow structure and flame development process in a selected high-tumble production engine. The endoscopic high-speed particle image velocimetry (eHS-PIV) was performed for varied engine speeds and intake valve closing (IVC) timings to evaluate their impact on the in-cylinder flow structure in a motored engine condition. On another endoscope engine sharing the same hardware, high-speed flame imaging was conducted to visualise spark stretch and flame propagation. The flow and flame measurements were repeated for over 100 cycles and the ensemble-averaged results are compared. The eHS-PIV showed that a strong tumble vortex is generated during the piston compression with the flow directed towards the exhaust side. As the piston reaches top dead centre (TDC), however, a complex flow breakup involving multiple flow components occurs. This is followed by lateral flow vectors travelling back towards the intake side, which is termed as the bounce-back flow. For a tested engine speed range of 1700–2700 revolutions per minute (rpm), 2500 rpm shows the most significant bounce-back flow as a result of competition between the remaining exhaust-ward tumble flow strength and the newly formed bounce-back flow strength. At a retarded IVC timing, the flow loss leads to a weakened tumble flow and subsequently no bounce-back flow formation to maintain the exhaust-ward TDC flow direction. From the comparison between the flow results and spark/flame high-speed images, a strong positive correlation is found between the TDC flow direction and spark plasma stretch, and subsequently the flame propagation direction. The findings indicate that the TDC flow direction should be considered as a key parameter in the engine design and operating condition settings.

The Tip Leakage Vortex Breakdown and its Possible Relationship With Rotating Instability in a Subsonic Compressor Rotor

The unsteady flow in the compressor at small mass flow rate has an important impact on the safety and efficiency of the compressor. Rotating instability was found in the experiment at near stall condition. Through URANS simulation, the origin of unsteady flow in an isolated subsonic rotor is studied. And the relationship between unsteadiness of tip leakage flow and rotating instability is revealed. With the deepening of the throttle, the flow field in the rotor changes from steady to unsteady. The intermittent spiral type breakdown of tip leakage vortex is considered to be the origin of the unsteady flow. Quantitative analysis of the tip leakage vortex shows the breakdown cycle caused by the interaction of the tip leaked vortex with the adjacent blade. When the tangential velocity and axial velocity of the leakage vortex reach a critical value, the tip leakage vortex will break. A radial vortex called back flow vortex will appear periodically after breakdown happens, which plays an important in rotating instability. The back flow vortex at upstream causes an overflow at adjacent blade leading edge, which results the next breakdown happens at downstream. Due to such feedback, the tip leakage vortex breakdown at two location alternately. A possible cause of RI was proposed: The spiral breakdown of the tip leakage vortex at different positions resulted in a cross-passage structure, which propagates into circumferential direction.

Grapevine berry shrivelling, water loss and cell death: an increasing challenge for growers in the context of climate change

Late ripening berry dehydration is an important phenomenon that occurs through grape berry water loss due to the alteration of the fruit water budget when transpiration and potential water back flow to the plant exceed the import of water into the berry through the phloem and xylem. Berry shrivelling can have a significant economic impact, reducing yields by ≥25 % with consequences on berry composition and the resulting wine. Its occurrence and consequences are expected to increase due to predicted climate change, shifting grape development and ripening into warmer periods (i.e., heat waves and drought events).

Method of calculating the total energy in suction and pressure pipelines of the main units at reclamation pumping stations

Purpose: theoretical substantiation of the method for calculating the total energy in suction and pressure pipelines of the main units at reclamation pumping stations to prevent unsteady processes and water hammer. Materials and methods: research and calculations were carried out at the pumping station “Mezhdurechye”, “Management of Stavropolmeliovodkhoz”, equipped with three main centrifugal pump units and two pressure pipelines. To calculate the total energy in the suction and pressure pipelines of the main pump, the entire pipeline network is divided into three sections: the first one is the intake, the second one is the distribution and the third one is the main pressure pipeline. For each section from 0.25 to 3.41 с²/м⁵ and the entire network 4.65 с²/м⁵, specific resistances were determined, the actual total head losses from 2.50 to 29.32 m when three units were fed into two pressure pipelines from 0.3 to 7.2 m³/s and hydraulic parameters of each unit: head (90.2 m), flow (2.67 m³/s), power (1585 kW), admissible vacuum suction head (4.2 m) at efficiency (88 %), with various operating options of the pumping station. Results: as a result of the research, the procedure for determining the total energy in the suction and pressure pipelines of the main units at reclamation pumping stations was determined, the total energy was calculated depending on the number of running pumping units: for suction pipelines from plus 0.1 to minus 1.5 m, for pressure pipelines from 75.79 to 86.34 m, which allows calculating the required hydraulic parameters of the booster pump used to close the back flow valve in the pressure pipelines of the main pump, to prevent backflow of water and water hammer before stopping the main pump. Conclusions: the above method is recommended for calculating in case of necessity the prevention of water hammer in the network by closing the back flow valve with a booster pump for reclamation stations equipped with centrifugal pumps with a maximum possible head of 120–130 m, in a complex operational option – the maximum number of pumps per one pipeline.

Desain dan Pengembangan Prototipe Alat Uji Pembangkit Listrik Tenaga Mikro Hidro dengan Back Flow Water System

Inovasi pengembangan Pembangkit Listrik Tenaga Mikro Hidro (PLTMH) terus dikembangkan mengingat kebutuhan akan energi listrik terus meningkat. Hal ini perlu didukung adanya media pembelajaran untuk mencari solusi alternatif permasalahan dalam mengatasi kebutuhan energi tersebut. Penelitian ini mendesain dan mengembangkan pembuatan PLTMH dengan back flow water system. Implementasi sistem berupa prototipe yang dapat digunakan sebagai media pembelajaran mahasiswa dan alat uji energi alternatif hidro. Metode perancangan dan manufaktur menggunakan metode Pahl & Beitz dan pengujian menggunakan metode eksperimen dengan cara pengamatan dan pencatatan data-data yang ditunjukkan pada alat ukur. Pengujian dilakukan dua tahap, pengujian pertama pada putaran kincir dan transmisi, pengujian kedua pada putaran dinamo dan voltase. Hasil pengujian menunjukkan bahwa sistem yang dirancang memiliki unjuk kerja yang baik.

Effects of Changes of Lake Victoria Water Levels on Land Use Patterns, Covid-19 Pandemic and Food Security in Winam Gulf, Homa-Bay County, Kenya

The study was carried out on the Southern shore of Winam Gulf, Homa Bay County, Kenya. It was aimed at establishing the relationship among changes of Lake Victoria water levels, land use patterns and food security during the COVID-19 pandemic. Empirical studies involving ground point survey was used to determine the extent of spread of the back flow and vertical rise of the lake’s waters from five pier and nine beach survey points between July 2019 to October 2020. In-depth interviews and questionnaires were also used to collect data which were analyzed using descriptive statistics and Likert’s scale. The average variations of the extent of the back flow was approximately 294m while the vertical change in the water levels along the pier points was 1.03m. This led to submergence of the adjacent land use patterns and interfered with food security in the region. Coupled with the impacts of COVID-19 pandemic, majority (209) of the respondents substituted their meals and a quarter (79) of the them reduced their number of meals per day. A strong positive perception on the responses by the Government of Kenya and County Government Homa Bay towards addressing the pandemic with the Likert’s scale summative perception index of 381 very effective, 328 effective and 363 satisfactory were realized. The study recommends: observance and execution of environmental laws governing settlement on riparian lands, proactive compliance with the warnings and advice from the meteorological department, and adoption of alternative land use patterns.