Air Mass Flow Research Articles

Study on the Effects of Inflow Parameters on the Auto-Initiation of Hydrogen-Rich Gas Rotating Detonation

ABSTRACT To obtain a comprehensive understanding of the auto-initiation characteristics of rotating detonation with the high-temperature hydrogen-rich gas. The experiment was carried out with hydrogen-rich gas as fuel and ambient temperature air as oxidant. The high-temperature hydrogen-rich gas was a kind of fuel-rich gas produced by the pre-combustion of hydrogen and oxygen. The effects of inflow parameters such as air mass flow rate, hydrogen mass flow rate, and hydrogen-rich gas temperature on the auto-initiation delay time and velocity of rotating detonation waves (RDWs) were experimentally studied. The experimental results showed that when the hydrogen and air mass flow rates were 6.3 ~ 17.4 g/s and 314 ~ 610 g/s, respectively, auto-initiation could be successfully achieved and a stable RDW could be formed. As the hydrogen and air mass flow rates increased, the auto-initiation delay times decreased from 40 to 5 ms and from 45 to 19 ms, respectively. When the temperature of the hydrogen-rich gas increased from 460 to 690 K, the auto-initiation delay time decreased from 100 to 10 ms, the RDW velocity decreased from 1368.5 to 1231 m/s. Hydrogen-rich gas has a high temperature, which is easy to cause the non-detonative combustion ahead of the wave of air and hydrogen-rich gas in the RDC, which consumes part of the fuel and resulting in a decrease in the RDW velocity.

A novel solar tower simulator for hydrogen regeneration by thermo-catalytic cracking of Ammonia: Energy, Exergy, and CFD investigations

This paper presents a novel concept of a central solar tower-based hydrogen regeneration system by thermo-catalytic cracking of ammonia. This includes a closed volumetric receiver for ammonia heating and cracking, a 2.45 kWe high-concentration radiation source, and an air-cooling system for the radiation source. The thermodynamic analysis shows that the net solar-to-hydrogen generation efficiency, first law efficiency, and exergy efficiency are 31 %, 82 %, and 79.8 %, respectively, for the optical efficiency of 35 %, the conversion efficiency of 99 %, and the waste heat recovery fraction of 20 %. The simulations with an ammonia flow rate of 1 kg/hr and flux concentration of 1200 Suns show the regeneration of 1.27 kg H2/day at Jodhpur and 1.57 kg H2/day at Ladakh. Monte Carlo ray tracing simulations revealed that the developed radiation source provides an average flux of ∼ 2 MW/m2 onto a spot size of 20 mm with an efficiency of about 31 %. Reynolds-averaged Navier Stokes-based analyses are used to design a novel air-cooling system for the radiation source. The computations show that (a) an unequal distribution of air mass flow rates at the front mḟ and back mḃ, should be preferred with mḟ>mḃ, and (b) for a total mass flowrate of 0.1 kg/s with mḟmḃ = 4, the maximum surface temperature of reflectors and Xe-arc lamps is less than 315 K and 610 K, respectively. The investigations revealed the feasibility of the concept and provided valuable insight for the planned experimental assessment and scale-up of the solar tower simulator.

Thermodynamic analysis of lined rock caverns for initial inflation and cyclic operational conditions in compressed air energy storage

With the irreversible trend towards cleaner and lower carbon energy alternatives on a global scale, the Lined Rock Cavern (LRC) compressed air energy storage technology emerges as a promising solution, offering vast prospects for large scale energy storage. This study explores the thermodynamic behaviors that arise from complex factors under high-frequency charging and discharging conditions in compressed air energy storage. It comprehensively considers transient gas flow, heat transfer, and real air properties, employing Computational Fluid Dynamics (CFD) methods. The simulations and analyses focus on the temperature and pressure variations inside the cavern during the initial inflation and cyclic operational conditions, along with the heat transfer characteristics of the sealing layer steel plate, concrete lining, and surrounding rock. As revealed by the research results, the inlet temperature and the air mass flow rate are two key factors affecting the average temperature inside the cavern during the initial inflation. Specifically, the inlet temperature shows a linear relationship with the average temperature while the air mass flow rate exhibits a nonlinear relationship. By fitting the simulation results, expressions that enable effective control of the average temperature are obtained. Under cyclic operational conditions, the pressure inside the cavern fluctuates within the range of 6 MPa to 10 MPa, displaying regular oscillations. With an increase in the number of cycles, the average temperature inside the cavern exhibits a decreasing trend, eventually stabilizing within a fixed range of fluctuations, indicating that the cavern has reached a steady state. The temperature of the steel plate and concrete lining undergoes significant changes throughout the entire operational cycle, influenced by both convective heat transfer and thermal conduction. With an increase in the number of cycles, their temperature variations align with the changes in the average temperature inside the cavern. In contrast, the temperature of the surrounding rock fluctuates within a narrow range throughout the process. The research findings of this study enable a more accurate estimation of the temperature variation range inside the cavern, facilitating the optimization of cavern design and providing crucial guidance for the application of lined rock caverns compressed air energy storage systems.

Research on operation characteristics of wind supercharged solar chimney dust haze removal street light

To realize distributed dust haze removal in street canyons, an innovative wind supercharged solar chimney dust haze removal street light is proposed. The design couples solar chimney technology with municipal street lighting, utilizing thermal pressure, chimney effect and wind supercharged wheel to power the system, which achieves the dual function of lighting and dust haze removal. Operational testing on a small-scale model showed: the airflow warms up the most in the inlet area, and the model creates updrafts with a dust haze removal effect. The filtration system consists of various filter screens arranged by descending filtration efficiency: HEPA, primary filter cotton, activated carbon and nylon filter screens, with airflow velocity in the flow runner in the opposite order. The average filtration efficiency is positively correlated with the pressure drop and negatively correlated with the overflow airflow. A combination of different material filter screens is more effective than simply increasing the thickness of a single filter screen. A single layer of 10 mm primary filter cotton has the highest total mass flow of clean air, reaching 4.18 g. HEPA has the highest average filtration efficiency at 93.1 %. This innovative approach offers an efficient solution for urban air purification while maintaining street lighting functionality.

Thermo-Economic Analysis of Thermoelectric-Based Atmospheric Water Harvesters: Flow Configuration Impacts

In recent years, thermoelectric cooling has seen significant growth, driven by advancements in nanoscience and manufacturing. Concurrently, the increasing water crisis in various regions has led to a surge in research on Atmospheric Water Harvesters (AWHs) for decentralized water harvesting. This study presents a comprehensive thermodynamic and economic analysis of Thermoelectric-based Atmospheric Water Harvesters (TAWHs) with different Heat Exchanger (HX) configurations with different flow configurations. Our research identifies five types of HXs, each characterized by its own optimal geometrical and controlling parameters. These HXs are evaluated based on economy, eco-friendliness, productivity, air cooling efficiency, and compactness. We provide new insights into the hidden potential and performance of Thermoelectric Coolers (TECs) in desalination, particularly highlighting the effect of increasing the ratio of surfaces mounted with TECs to the total surface area of the channels. Our results indicate that among the HX configurations, the counter flow HX is the most economical option, capable of water harvesting at a cost of $0.230 USD per liter from an 80% humidity level. The parallel flow HX demonstrates higher efficiency according to the second law of thermodynamics and environmental friendliness, while the crossflow HX exhibits lower overall efficiency. We found that the optimum cold channel incoming air flow rate varies with humidity in a detailed analysis of a counter flow HX with 2 columns and 15 rows. Interestingly, we found that humidity and incoming air mass flow rate have a negligible effect on power consumption. This work can be used as a guideline for future engineering problems involving the design and optimization of TAWHs.

Modeling and Control of Multi‐Stack Fuel Cell Air System based on Nonlinear Model Predictive Control Method

Hydrogen is crucial for achieving SDGs by driving energy transition and combating climate change. Proton exchange membrane fuel cell technology, leveraging hydrogen, faces challenges in meeting high‐power demands. The multistack fuel cell system (MFCS) tackles this by integrating multiple substacks, yet its air supply needs meticulous control. Proportional integral derivative (PID) decoupling from single‐stack falls short of MFCS. This article proposes nonlinear model predictive control (NMPC) for optimized air flow and pressure decoupling. Modeling MFCS's air system and designing a predictive model, it is aimed to ensuring precise control of air flow and pressure in each substack. The decoupling experiments show that NMPC outperforms PID, accurately managing air flow and pressure and reducing load fluctuations. For air mass flow, NMPC cuts mean‐absolute error (MAE) by 64.56% and root‐mean‐square error (RMSE) by 81.36%. For pressure, MAE drops 81.23% and RMSE 83.59%. Comprehensive step load tests confirm NMPC's precise, dynamic regulation too, compared to PID, NMPC lowers average MAE for air mass by 20.67%, pressure by 32.22%. RMSE improvements of 31.08% and 33.23% highlight NMPC's strength. NMPC's quick response mitigates coupling issues, enhancing vehicle load adaptability.

Evaluating long-term operational data of a Very Large Crude Carrier: Assessing the diesel engines waste heat potential for integrating ORC systems

Given the spotlight on waste heat recovery (WHR) technologies for decarbonizing the shipping industry, critically assessing waste heat from propulsion and auxiliary engines using actual data is crucial for accurately predicting fuel and carbon savings. This paper addresses this by applying advanced data processing, considering voyage characteristics, and developing methods for mapping waste heat from main engine (ME) and diesel gensets (DGs) operations using long-term operational data from a Very Large Crude Carrier (VLCC) case study. Two methods predict unrecorded air mass flows by implementing heat balance: one using measured temperature values and the other estimating exhaust gas mass flow rates based on fuel oil consumption. Within the main objectives of this study is to examine the impacts of employing the exhaust gases of both ME and DGs to evaporate recuperative ORC working fluid on power output and vessel annual carbon savings, with the formed diesel engines operational profiles serving as inputs. Simulations show a power output of 530 kW using ME exhaust gases, increasing to 653 kW and 741 kW with DGs integration for R245fa and R1233zd(E) as the selected ORC working fluids, respectively. The proposed solutions can reduce annual CO2 emissions by 4 % to 7 %.

CFD modeling of a modern wood stove - Soot formation

Wood stoves are important domestic heating appliances using renewable bioenergy. However, the emission of Particulate Matter (PM) is the major concern for the application of wood stoves. Thus, improvements in the design of wood stoves are required for the reduction of PM emissions (mainly soot) to fulfill the increasingly stringent pollutant emission limits. To achieve low PM emission of the wood stove, a 3D steady-state CFD model is used to simulate the wood stove with a focus on soot formation in this study. The model is evaluated with the experimental data, the results of which show that the CFD model provides a reasonable prediction of wood stove experiments, indicating that the CFD model can be used as an efficient tool to optimize the design of the wood stove. The model is further used to study the effects of injection direction and mass flow rate of the tertiary air on the soot particle emission. It is found that the horizontal- and down-direction injectors can effectively reduce soot formation and an optimized tertiary air mass flow rate exists in the modern wood stove system. These conclusions are very useful in designing and developing the intelligent control system of the modern wood stove.

Investigation of the utilization of forest woodchips in a commercial small-scale open-top gasifier

The present work investigates the gasification of forest woodchips, which also contain needles, branches and cones, in an 85-kW open-top gasifier with 60 %–100 % load. This lower quality fuel has higher contents of ash, bark and fines compared to typical requirements of commercial small-scale gasifiers. The woodchips were utilized in unsieved and sieved (>10 mm) fraction. By using gas analysis and temperature measurements at a high local and temporal resolution, three main novel results were found: 1) The results of this work confirm that preferential paths in the fuel bed, caused by the fines content, led to a worse gas quality. The positive effects of a load reduction (i.e., increasing hydrogen and decreasing tars contents) were not found with the unsieved fuel. 2) Opposite trends for the methane concentration with the load were found with unsieved and sieved fuel. The preferential paths probably prevented the complete decomposition of longer-chain hydrocarbons and increased the intermediate product methane, while the non-methane hydrocarbon content reduced at a similar rate with both fuel fractions. 3) When using unsieved fuel, reducing the load massively decreased the fluctuations of the air mass flow and the total hydrocarbon content. With sieved fuel, however, a satisfying process stability was already achieved in all loads. Therefore, an appropriate load management was identified to enable the utilization of fuels with higher fines contents. With these new findings, forest chips in unsieved and sieved form can be successfully used in small-scale open-top gasification.

Determination Of Two-Phase Flow Regimes Of A Condensing Water-Air Mixture In An Array Of Micro Channels

Proton exchange membrane (PEM) full cells (FCs) are a promising alternative to combustion engines for mobile applications. Their signature low operating temperature leads to the possible existence of product water in its liquid form. Liquid water formation and transport are important phenomena to understand and model in order to facilitate the development of new, more efficient PEMFCs. This contribution investigates the two-phase flow phenomena separately by introducing a gaseous air-vapor mixture into an optically accessible fuel cell flow plate with 14 parallel micro channels (confinement number Co = 7.3) and a carbon paper inlay representing the FC's gas diffusion layer and bringing it to the point of onset of condensation. Special care is taken to provide a controlled and reproducible air-vapor mixture with low pressure pulsation. One key feature of the experiment is that the flow plate used is designed to be as similar to a regular research fuel cell flow plate as possible, retaining its channel surface properties and electrical parameters. It can also be heated to a given temperature to mimic the fuel cell operating conditions. Therefore, the same plate can also be used in in-situ experiments in an operated fuel cell. An air mass flow rate of 500 - 1000 mLn / min with relative humidities of 75% - 95% at 65°C and 75°C was investigated. The emerging flow patterns were captured using a high-speed camera at 250 Hz and categorized using canonical two-phase flow regime nomenclature. It is shown that the present setup can produce the relevant two-phase flow patterns that can be found in operated fuel cells as reported by previous studies and is furthermore equipped to investigate flow states not easily reached with an operated fuel cell (e.g. flooded channels).

Effect of channel depth ratio and absorber plate configuration on performance of a solar air heater

An experimental evaluation of the effect of channel depth ratio and absorber plate configuration on the performance of a baffled counter flow double-pass solar air heater (BCDSAH) is main objective of current work. The BCDSAH was constructed so as to permit adjustments of channel depth ratio (CDR) to 2, 3 and 4. During experimentation, the lower channel depth was kept at 50 mm while the upper channel depth was adjusted to 100 mm, 150 mm and 200 mm, yielding various channel depth ratios. The assessments were conducted for three configurations of absorber plate: (i) flat absorber plate, (ii) baffled absorber plate and (iii) baffled absorber plate with phase change material (PCM). The performance of the BCDSAH was evaluated at an air mass flow rate of 0.07 kg/s for temperature rise, useful heat gain (UHG), energy efficiency, and exergy efficiency. For CDR = 2 and a baffled absorber plate with PCM, the obtained average values of temperature rise, UHG, energy efficiency and exergy efficiency were 15.3 °C, 1075.2 W, 76.2 % and 2.7 % respectively. For the baffled absorber plate with PCM, increases of 8.5 %, 9.4 %, 10.1 % and 10.9 % were obtained in temperature rise, UHG, energy efficiency and exergy efficiency respectively for CDR = 2 compared to CDR = 4. Finally, a value of CDR = 2 and a baffled absorber plate with PCM are suitable for applications like drying of agricultural products and space heating.

Experimental Investigation of the Sensitivity of Forced Response to Cold Streaks in an Axial Turbine

In turbomachinery, geometric variances of the blades, due to manufacturing tolerances, deterioration over a lifetime, or blade repair, can influence overall aerodynamic performance as well as aeroelastic behaviour. In cooled turbine blades, such deviations may lead to streaks of high or low temperature. It has already been shown that hot streaks from the combustors lead to inhomogeneity in the flow path, resulting in increased blade dynamic stress. However, not only hot streaks but also cold streaks occur in modern aircraft engines due to deterioration-induced widening of cooling holes. This work investigates this effect in an experimental setup of a five-stage axial turbine. Cooling air is injected through the vane row of the fourth stage at midspan, and the vibration amplitudes of the blades in rotor stage five are measured with a tip-timing system. The highest injected mass flow rate is 2% of the total mass flow rate for a low-load operating point. The global turbine parameters change between the reference case without cooling air and the cold streak case. This change in operating conditions is compensated such that the corrected operating point is held constant throughout the measurements. It is shown that the cold streak is deflected in the direction of the hub and detected at 40% channel height behind the stator vane of the fifth stage. The averaged vibration amplitude over all blades increases by 20% for the cold streak case compared to the reference during low-load operating of the axial turbine. For operating points with higher loads, however, no increase in averaged vibration amplitude exceeding the measurement uncertainties is observed because the relative cooling mass flow rate is too low. It is shown that the cold streak only influences the pressure side and leads to a widening of the wake deficit. This is identified as the reason for the increased forcing on the blade. The conclusion is that an accurate prediction of the blade’s lifetime requires consideration of the cooling air within the design process and estimation of changes in cooling air mass flow rate throughout the blade’s lifetime.

Interpretasi Fase Awan dengan Metode CCO Dan RGB pada Data Satelit Himawari-9 di DKI Jakarta (Studi Kasus: 1 Januari 2023)

Indonesia is the largest archipelagic country in the world so it receives large amounts of energy from solar radiation which makes it the most active convective region in the world. In December and January, DKI Jakarta tends to experience the rainy season. On January 1 2023, BMKG gave an early warning that it would rain in Jakarta. Reporting from several news reports, in the new year 2023, Jakarta was hit by heavy rain. Cloud phase analysis is needed to determine the potential for rain. This research identifies cloud phases using Himawari-9 satellite image data which is then processed using the Cloud Convective Overlays (CCO) method and the Red Green Blue (RGB) method. The CCO method can identify the distribution of cumulonimbus clouds and the RGB method can determine the flow of air masses, the type of air mass (Airmass), identify cloud phase, and the presence of high clouds containing ice (Day Convective Storm, Day Natural Color, and Cloud Phase Distinction ). The data used are bands 3 (0.6 µm), 5 (1.6 µm), 7 (3.7 µm), 8 (6.2 µm), 10 (7.3 µm), 12 (9.6 µm), 13 (10 .4 µm), and 15 (12.4 µm) at 7.00, 8.00, 9.00, 10.00, 11.00, 12.00, 13.00, and 14.00 WIB (GMT+7). The data was processed and visualized using Grid Analysis and Display System (GrADS) and GMSLPD SATAID software.

Optimal Design and Performance Analysis of a Gas-Gas Heat Exchanger for Harvesting Waste Heat

This study reports the design of an optimized heat exchanger capable of efficiently extracting and transferring waste heat from flue gas to air. An experimental setup was constructed to recover waste heat from the exhaust steam of a boiler, using this heat to warm compressed air. Thermocouples recorded the temperatures at the inlet and outlet of both the hot and cold fluids. A MATLAB code is developed to compare the experimental results. According to our code, the cold fluid outlet temperature ranged from 71.5°C to 76°C, while the experimental setup showed temperatures ranging from 66°C to 71.5°C at air mass flow rates of 0.1564, 0.1346, and 0.1794 kg/s. The deviation may arise from the inaccuracies of the flow rate and the temperature measurement devices as well as the constraints in correlations which calculate heat transfer coefficient and friction factor in pressure drop. Future work may focus on minimizing the deviations and propose an improved design of heat exchanger. IUBAT Review—A Multidisciplinary Academic Journal, 7(1): 124-141

VALORIZATION OF ONION AND TOMATO THROUGH SOLAR DRYING: CASE OF THE SHELL SOLAR DRYER

One of the most widely grown vegetable crops in Burkina Faso is onion and tomato. Solar drying is crucial for the conservation of these products. One of the most accessible solar dryers is the shell solar dryer, which allows these products to be dried hygienically. We were able to obtain some results from the experiment carried out over three typical days with a solar dryer which shelled 1116 g of onion and 695 g of tomato cut and distributed on the three racks of the dryer. We observed a total water loss of 456 g for the onion and 257 g for the tomato from the first to the third day of the experiment. The shell solar dryer has an efficiency of 29.88% with an inlet temperature of 33°C, an outlet temperature of 76°C and an air mass flow rate of 0.004 kg/s. The average solar irradiation is 579 W/m 2.

Reducing convective losses in a solar cavity receiver VoCoRec by creating a controlled vortex of returned air

The efficiency of air-type solar towers influences the minimal cost of electricity/heat produced by them, which limits their use despite the widespread use of many forms of concentrated sun power plants. Nonetheless, the temperature potential of this kind of concentrated plant is the highest. To improve the efficiency of an air-type solar tower, a technique for reducing convective energy losses with return air is therefore suggested. In order to increase a cavity receiver's thermal efficiency, a little-known concept called vortex creation will be discussed in this work. The article models different ways of creating an air vortex inside the cavity receiver. Using the VoCoRec design as an example, cases are shown where the vortex increases and decreases the thermal efficiency of the receiver. The concept of Air Return Ratio (ARR) is used to determine the convective losses in a solar collector. This coefficient indicates the convective losses of the receiver due to buoyancy forces and has a direct proportional dependence on the convective efficiency coefficients of the receiver. The VoCoRec receiver, which incorporates the directional vortex inside the receiver, increased the air return coefficient by 4 % (at the same air mass flow rate). The dependence of the air return coefficient on different angles of the air outlet to the absorber plane, including in the radial direction, was also investigated. Increasing the angle of inclination of the air outlet to the main absorber increases the air return coefficient in all cases, but also increases the aerodynamic drag of the receiver (pressure drop).

Investigation of the effect of dimensional and non-dimensional parameters on the performance of pitch-varied staggered arranged dimple solar air heaters

In this study, the efficacy of a single pass, single glazed, five different types of absorber plate incorporated solar air heater (SAH) was experimentally examined in outdoor test conditions on alternative days. The experiment was carried out for flat plate solar air heater (FPSAH) and staggered arranged dimple imprinted absorber plate solar air heater (SDPSAH) maintained at four different pitch ratios (Pt/Pl: 1.0, 1.11, 1.25, and 1.67) by varying the air mass flow rate (ma) from 0.01-0.05 kg/s (corresponding Re range: 1971.66–10466.45). The results show that the performance of both FPSAH and SDPSAH improves when the ma increases. For the tested range of ma, SDPSAH outperforms FPSAH regardless of pitch ratio. SDPSAH, with a pitch ratio of 1.25, on the other hand, has a greater air temperature difference, efficiencies, heat removal factor, collector efficiencies, and averaged Nusselt number (Nuavg) while having a lower global heat loss coefficient and top loss. The Nuavg of SDPSAH at a pitch ratio of 1.25 is 1.01–1.17, 1.16–1.24, 1.26–1.57, and 1.44–1.88 times higher than SDPSAH at pitch ratios 1.0, 1.11, 1.67, and FPSAH, respectively. The higher averaged friction factor (favg) of 0.0443 is attained for SDPSAH at a pitch ratio of 1.25 due to the presence of the largest number of dimples. The ηth and ηd of SDPSAH at a pitch ratio of 1.25 are 34.5 and 35.5 % higher than those of FPSAH. The global heat loss coefficient of SDPSAH at pitch ratios 1.11, 1.0, and 1.67 is 1.05–1.84, 1.09–2.15, and 1.11–2.92 times higher, respectively, than that of SDPSAH at a pitch ratio of 1.25.

Utilization of vortex flow pattern in the design of an efficient solar air heater

In this work, numerical and experimental analyses of a new model of circular solar air heater are carried out to examine the effect of employing vortex flow inside the air vessel of collector for convection enhancement. In three-dimensional numerical CFD-based analysis, the COMSOL Multi-physics is used to solve the flow equations for the turbulent forced convection airflow and conduction equation for the solid parts of the solar heater at different air mass flow rates in the range of 0.003 to 0.012 kg/s. In the calculation of turbulent stresses and heat fluxes, the RNG κ-∊ turbulence model is employed. The surface to surfaces (S2S) radiation model is used to consider the radiations emitted by the hot surfaces in collaboration with the energy equation. For validation, the theoretical findings are evaluated against the experiment. For the studied test cases with different values of solar irradiation and air mass flow rate, thermal efficiencies of up to 80 % are found. In comparison to the conventional rectangular-shaped solar air heaters with smooth ducts, more than 100 % increase in the value of thermal efficiency is delineated from the theoretical and experimental findings. This gain is attributed to the unique flow pattern in the developed solar collector.

Applicability of Variable-Geometry Turbocharger for Diesel Generators under High Exhaust Back Pressure

The exhaust back pressure of diesel engines is becoming increasingly higher nowadays. In order to keep discharging exhaust unhindered and operating smoothly under high exhaust back pressure, a large reduction in engine maximum brake output is often observed, as well as increased fuel consumption and lower combustion efficiency with heavy exhaust smokes. In our previous study, “Applicability of Reducing Valve Timing Overlap for Diesel Engines under High Exhaust Back Pressure”, a reduced valve timing overlap of 12 °CA partially improves the brake output and BSFC for a fixed-geometry turbocharged diesel engine under high exhaust back pressures. A potential solution for restoring the brake output under high exhaust back pressures could be the use of variable-geometry turbochargers. In this study, a variable-geometry turbocharger is applied to a diesel engine to study the engine performance characteristics and applicability, especially the further improvement of brake output and the brake-specific fuel consumption of the engine. Continuing with the results of our previous research, a basic setting of 12 °CA for the valve timing overlap is set up for the subsequent engine performance simulations in this study (using GT-Power SW). Via simulation, exhaust back pressures of 25 kPa, 45 kPa, and 65 kPa gauge are studied for a turbocharged diesel engine. The results for the engine parameters, including brake output, brake-specific fuel consumption, compressor outlet temperature, turbine inlet temperature, intake air mass flow rate, and exhaust mass flow rate are analyzed. The results of the variable-geometry turbocharger, including turbocharger speed, pressure ratios and efficiencies of compressor and turbine are also analyzed. The results indicate that the brake output and brake-specific fuel consumption are effectively improved under full-load operation with an adequate variable-geometry turbocharger rack position. Operable ranges of rack position are also set up for different back pressures.

Warm‐Season Drying Across Europe and Its Links to Atmospheric Circulation

AbstractWe study drying trends across the central latitude strip of Europe (47.5–52.5°N and 2.5–27.5°E) during 1980–2019 and their links to atmospheric circulation. Daily differences between potential evapotranspiration and precipitation (PET–P) calculated from the E–OBS data are used to characterize dryness, and atmospheric circulation is represented by circulation types classified using daily sea level pressure patterns from the NCEP/NCAR reanalysis. Circulation types favoring dry conditions in vegetation season (April–September) are identified based on daily PET–P, and their temporal changes, seasonal variations, and links to trends in dryness in individual European regions are analyzed. In the early vegetation season (AMJ), drying trends are observed mainly in Western and Central Europe while in the late vegetation season (JAS), they are located predominantly in Eastern Europe. The dry circulation types include all anticyclonic types in all regions, as well as northeast to south (southwest in Eastern Europe) directional types. Trends of the dry circulation types correspond to those of dryness: the largest increase is found during AMJ in Western and Central Europe but during JAS in Eastern Europe. The results show that trends in dryness in the central latitude strip of Europe in the warm half‐year were associated with changes in atmospheric circulation, as the largest increases in frequency of dry circulation types occurred in the regions and months affected by pronounced drying. The increasing frequency of anticyclonic types in AMJ and reduced inflow of moist air masses from the Atlantic are the key factors supporting intensification of dry conditions in European mid‐latitudes.