Advanced Materials Research Vol. 1016

Abstract: In-cylinder flow such as tumble and swirl has an important role on the engine combustion efficiencies and emission formations. In particular, the tumble flow whichis dominant in current high performance gasoline engines has an important effect on the fuel consumption and exhaust emissions under part load conditions. In this research a numerical analysis on a single cylinder engine using computational fluid dynamics (CFD) is presented. From the results of the commercial code, the tumble, cross-tumble and swirl ratios are calculated for evaluating the flow development through intake and compression strokes. The reliability of the results is accessed through a validation process, which consists of comparing numerical and experimental results for in-cylinder pressure, along with a grid independence study. The results for the in-cylinder pressure show good agreement between numerical and experimental results, and the grid independence is rapidly achieved. The results for rotational ratios around X and Z axis show lower and unstable values, and indicate that the vortex on those plane change its rotation direction. On the other hand, the ratio around Y axis has the greater values, and also keeps its rotation direction.

Abstract: Theincrease of greenhouse gases emissions makes necessary to improve the comprehension of the Internal Combustion Engines operation. One of the factors that affect the combustion in these engines is the turbulence, since it can raise the quality of the fuel-air mixture inside the combustion chamber. However, when modeling internal combustion engines using CFD, the turbulence model choice is always a relevant problem. The present paper analyzes the results for three different turbulence models (k-ε Realizable, RNG k-ε and Menter k-ω SST) ina single-cylinder engine geometry, comparing numerical and experimental pressure data. For this experiment, the k-ε models obtained more trustable results than the k-ω SST, using less computational resources. The models achieved good results for eddy recirculation inside de cylinder and in regions of free shear flow at the valve openings, which makes possible to observe the correlation between parameters such as tumble and turbulent kinetic energy.

Abstract: Torque, as an important indicator of the engine, is the reflection of performance of cylinder-embedded piston engine. In power stroke, torque varies at different moments, so if the impact of structural parameters on torque needs to be analyzed, the values of torque in power stroke need to be added together and divide lasting time. The average effective torque is the average of the torque generated by explosive force during the entire power stroke, which overcomes the disadvantages of the instantaneous torque which can not reflect the changes in power process. Therefore, the influence of each structure size on the force transmission performance can be analyzed with maximizing the average effective torque. It is concluded that for increasing the average effective torque, the radius of the hinge center trajectory of cap R should be increased, and the length from rotating center O to the trajectory of piston H should be decreased. The length of rod L has little influence on the average effective torque. However, if there is a too large D-value between R and H, the rod may deflect seriously, so that the piston side force increases, causing the piston wear and tear. So the values of R and H should be selected with specified conditions in the design.

Abstract: Flashing is an important factor in the working process of hot water rocket motor. In order to deeply understand the performance characteristic of hot water rocket motor, a numerical simulation model of the flow field in the nozzle was established in this paper. According to the study of flow field in the nozzle of the motor,it is found that the phase change occurs at the position of the throat,and the flow reaches to supersonic after the throat because of the changing sound speed.The flow in the nozzle can be divided into three processes in this paper: single-phase flow process, flash process and expand-accelerating process.

Abstract: In aim to gain the capability of providing variable thrust, the technology of an axial pintle inserted into the nozzle of the solid rocket motor had been used. As the pintle inserted into the nozzle, the loss of specific impulse will increase. In order to reduce the loss of fluid dynamics of the pintle nozzle, considering the interaction of the nozzle contour and the pintle contour, CFD method combined with the response surface method is used to optimize the contour of the pintle nozzle. The central composite design is used to introduce a design point; the Kriging algorithm is used to generate the response surface; and the Nonlinear Programming by Quadratic Lagrangian is used for optimization. After the optimization, the loss of fluid dynamics can be reduced significantly. To study the influence of the key parameters to the loss of specific impulse, the key parameters are optimized independently in this paper. It indicates that the main factor of the loss of specific impulse is the parameters of the nozzle. To reduce the computational consumption, the process of optimization has been improved. And the result shows that when optimizing a pintle nozzle, the nozzle part and the pintle part can be optimized separately. The method that bases on the response surface not only takes into account of the interactive effects of the shape parameters, but also works with less calculation. Additionally it maintains the high accuracy and reliability. It can be used to select the optimal shape parameters of the pintle nozzle quickly, which has certain engineering application value.

Abstract: This paper discusses the cooperative control for formation keeping of fractionated spacecraft, which is a new concept in recent years. For system of second-order differential equations of formation flying dynamics, knowledge of graph and consensus theory is introduced in study. By means of the idea of sliding mode control, we design a tracking control law for time-varying desired signal. Via exchanging error information among modules, the control law can make errors synchronized up to zero to achieve tracking. Relative velocity information between modules is not needed in this control law, which will efficiently reduce the requirements for relative navigation between modules. Then we prove the stability of the control system. Finally numerical simulation results show the effectiveness of the control law. By configuring the control parameters reasonably, we can achieve high degree of control accuracy.

Abstract: The main goal of the present work was to assess and test a pilot assisting technique for light aircraft with inexperienced volunteers. The pilot assisting technique consisted of modified PID controllers with gain scheduling, with features to maintain the pilot authority and flight safety, simplifying the piloting. After the gain adjustment, the controlled model (pilot assistance) was adapted into a simulation platform of the ACS-100 Sora aircraft at CEA-UFMG and volunteers were invited to simulate a flight in a predefined trajectory. It was possible to conclude that inexperienced volunteers were able to improve significantly on this task.

Abstract: Permanent magnet synchronous motor (PMSM) has been widely in production and everyday life, and its control system has been a difficult point needing more researches. Therefore, it is important to investigate the control system of PMSM. In order to ensure the dynamic and static performance of PMSM, this paper presents a new vector control method based on the rotor field oriented control (RFOC) technology. The paper introduces the fundamental principal of RFOC, and designs three loop servo control simulation system and analyses the result of the simulation. The results shows that the RFOC system has high dynamic and static performance by adopting the three loop control. And the analysis can also provide a reference for similar servo control system design personnel.

Abstract: This paper presents a case study for the design and implementation of real-time harmonic monitoring at the main 3-phase 4-wire distribution system in a shopping center. The implemented monitoring system automatically acquires real-time data from a power-quality measuring instrument over Ethernet connection. The acquired data are subsequently stored in a database and can be retrieved for further processing and analysis. As a result, harmonic currents of all three phases and a neutral can be monitor up to 31^st order.

Abstract: In this paper, a Fault-Tolerant Control strategy (FTC) was applied using a linear dynamical model of a business jet aircraft subjected to actuation faults. As a baseline controller, an optimal linear quadratic tracker was designed to control some selected aircraft motion variables. Faults due to the loss of effectiveness were assumed. Then, the FTC was built upon a compensation of faults into the dynamical equations. The complete system was tested using nonlinear simulations of the aircraft dynamics. The results demonstrate the ability of the FTC strategy to maintain the stability of the system and to improve the tracking performance for a large scope of faults.