Search Results (6)

Based on the three-dimensional (3D) steady-state CFD numerical simulations conducted previously on an industrial Kalugin top combustion hot blast stove, a two-dimensional (2D) transient CFD numerical model for a single channel (hole) of a column of checker bricks in the regenerator of the same hot stove was established in the present work. The average mass flowrate and temperature of the flue gas flowing into the checker brick holes during the combustion period predicted by the 3D model were used as the inlet boundary conditions of the 2D model. Inside the hole of the checker bricks, processes of fluid flow and heat transfer of the flue gas during the combustion period and those of cold air during the hot-air-supply period were simulated using the 2D model for multiple operation cycles (combustion and hot-air-supply periods) of the hot stove, enabling rapid predictions of hot-air temperature under different operating conditions. The simulation results show that when the fuel gas flowrate and air consumption coefficient during the combustion period are controlled within the range of 80,000–100,000 Nm³/h and 1.02–1.28, respectively, a hot-air temperature in the range from 1273 °C to 1295 °C can be obtained during the hot-air-supply period. Applying this optimized operating condition to the industrial hot stove investigated in this study can achieve significant effects of reducing fuel gas flowrate by 8.6% and increasing hot-air temperature by 32 °C. In addition, a regression analysis on the numerical simulation results and the data measured from the industrial hot stove yields a roughly linear relationship between the dome temperature during the combustion period and the hot-air temperature during the hot-air-supply period, that is, the hot-air temperature would be increased by about 16 °C for every increment of 10 °C in the dome temperature, for instance. Therefore, the influences of the operating parameters on heat transfer characteristics in the regenerator and on hot-air temperature obtained in the present work provide a useful reference for guiding the hot stove operation optimization to achieve significant energy saving and emission reduction through facilitating more efficient combustion to minimize fuel gas consumption in steel plants. Full article

A theoretical study of the dynamic closed-loop behaviour of a reactor/feed-effluent heat exchanger (FEHE)/furnace system for the catalytic combustion of volatile organic compounds (VOCs) is presented. A 1D pseudohomogeneous plug-flow model is proposed to simulate the non-steady-state operation of the monolith reactor and the FEHE, while the furnace behaviour is described by means of a heterogeneous model of lumped parameters. Positive energy feedback is a source of instability that leads to strong thermal oscillations (limit cycles) and may cause damage to the equipment and sintering of the catalyst. The design of a robust and flexible control system and an efficient control strategy are, therefore, required to ensure safe and stable operation. The response of the system under three different control strategies to the most frequent disturbance variables—the feed flowrate (F_V0) and feed concentration of VOCs (C_0Et)—was evaluated. One of the control strategies consisted of a single-loop feedback system with servomechanism changes in the reactor inlet temperature (T₀) that manipulated the bypass valve and, sequentially, the natural gas flowrate in the furnace (F_NG). This approach made it possible to meet the control objective (reducing VOCs) without losing controllability and while minimizing the use of external fuel. Full article

The bulldozer is a mobile earthmoving machine with a differentially steered mobile base and an onboard manipulator used for soil cutting and transportation. Grading the ground to match a desired contour is an end-effector path-following task, with required joint rates dependent on mobile base motion. The offline planning of travel velocity profiles that respect the available hydraulic flowrate limits is difficult due to uncertainties in the machine–soil interactions. Hence, we propose a flow-bounded velocity controller enabling accurate automatic grading with online velocity scaling. The capacity of hydrostatic transmission and manipulator actuators, as well as the desired velocity, are considered when deciding the commanded velocity reference for the mobile base. Our dynamic simulation results show that, with the proposed controller, a desired ground profile is cut accurately when the machine operates at its performance limits. Comparison to constant velocity driving shows that errors in blade positioning are reduced dramatically. Constant velocity selected to keep the flow within limits results in longer completion times compared to our solution, making it more time optimal. Furthermore, the rpm of the diesel engine can be reduced to save fuel without compromising control performance. Full article

Fuel flowrate control system and fuel thermal management are very important for aeroengine and the overall aircraft, and it has been researched for several decades. This survey paper makes a comprehensive and systematic overview on the exiting fuel flowrate regulation methods, thermal load of fuel metering units, fuel-based thermal management, and the fuel tank’s thermal management topology network with drain and recirculation. This paper firstly reviews the mechanism, technical advantages, and technical challenges of the fuel metering unit with flowrate control valve and constant pressure difference valve compensator, flowrate control valve and variable displacement pump-based pressure difference compensator, and motor-based flowrate regulation. Then, the technical characteristics of above fuel flowrate control methods related to thermal management are discussed and compared. Meanwhile, the behaviors of recirculated fuel flow within single tank system and dual tank system are explored. Thirdly, the paper discusses the future directions of fuel flowrate control and thermal management. The survey is significant to the fuel flowrate control and fuel thermal management of the aircraft. Full article

Stable operation of fuel cell air compressions is constrained by rotating surge in low flowrate conditions. In this paper, a diagnosis criterion based on wavelet transform to solve the surge fault is proposed. First of all, the Fourier transform was used to analyze the spectral characteristics of the outlet flowrate. Before wavelet transform was used, the data are standardized. This step eliminated the influence of the flowrate’s absolute value. Then, the wavelet coefficients under characteristic frequencies were extracted. Finally, the diagnosis criterion’s threshold, which indicates the surge occurrence, was defined from the perspective of safety margin. The criterion threshold alerted a surge only 1 s after it occurred. The analysis results show that the criterion meets with the expectation, and it can be used for the control of anti-surge valve. Full article

The demand for internal combustion engines remains high for mobile power sources in all fields due to their low costs, running distance capacity, charging reliability, and heavy driving durability. However, air pollution, efficiency, and environmental factors make this more challenging. According to recent research, using a fueled prechamber can lead to lean combustion in the main chamber, resulting in increased efficiency, reduced fuel consumption, and reduced toxic emissions. However, difficulties in producing a fueled prechamber for commercial engines include mixture and soot formation problems in the limited space of the prechamber, and limited research on the charging possibility of the unfueled prechamber. A removable prechamber is advantageous for used vehicles because an engine redesign is not required. Therefore, we proposed to use an unfueled prechamber to enhance the lean burning efficiency of the spark ignited (SI) engine and explore the possibility of charging an unfueled, unscavenged prechamber with a fuel-rich mixture. Consequently, investigating the possibility of filling an unfueled prechamber with a fuel-rich mixture without additional fuel delivery or an air control system was the aim of this study. For this purpose, the charge flowrate of the centrally located unfueled prechamber is extensively investigated by using Computational Fluid Dynamics (CFD), through its design. As a result, a realizable charge flow was detected for the unfueled prechamber in two periods in the inlet and compression strokes. Most importantly, we found fluctuation phenomena in mass flow rates at the inlet stroke directing a charge flow of the richer mixture into an unfueled prechamber without additional systems. Moreover, keeping the charged rich mixture inside the prechamber during the compression stroke is as important as charging the prechamber with the fuel-rich mixture. The study will enable us to produce a removable prechamber to improve the combustion efficiency of port injected engines. Full article