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Now showing items 1 - 16 of 27

  • Research on combustion process of a free piston diesel linear generator

    Feng, Huihua   Guo, Chendong   Yuan, Chenheng   Guo, Yuyao   Zuo, Zhengxing   Roskilly, Anthony Paul   Jia, Boru  

    Highlights • We study the exothermic properties of the FPDLG during the combustion process. • We compare the combustion of TRE with FPDLG, and reveal the heat releasing characteristics of FPDLG. • We validate the model with test data from a running FPDLG prototype. Abstract The piston motion of a free-piston diesel linear generator (FPDLG) is different from the traditional reciprocating engine (TRE). Here we focused on a numerical simulation for the research on the combustion process of an FPDLG by adopting coupled models of zero-dimensional dynamics and multi-dimensional computational fluid dynamics (CFD). Piston dynamics model and CFD model to simulate the combustion process were set up based on the calculated results of free-piston motion, which were validated with tested data from a running FPDLG prototype. According to the coupled parameters of these two models, we studied the exothermic properties of the FPDLG during the combustion process through iterative computation, and compared the simulation results of a TRE to a FPDLG with comparable and similar structural parameters. The results indicated that, combustion in the FPDLG lasted for a longer time compared with that in the TRE. While the heat release before top dead center (TDC), the isochoric heat release, and the heat release during the rapid combustion period were low, the post-combustion became more intense. Furthermore, the average temperature in the cylinder was generally lower, while became higher in the end of expansion stroke. In addition, the maximum combustion pressure was lower and lasted for a shorter time.
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  • Piston dynamics analysis considering skirt-liner dynamic clearance

    Tian, Jingyi   Feng, Huihua   Feng, Yuanjie   Yang, Zhengwei   Zhu, Chengjun   Li, Jiegui  

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  • Stable Operation and Electricity Generating Characteristics of a Single-Cylinder Free Piston Engine Linear Generator: Simulation and Experiments

    Feng, Huihua   Song, Yu   Zuo, Zhengxing   Shang, Jiao   Wang, Yaodong   Roskilly, Anthony  

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  • Research on the intermediate process of a free-piston linear generator from cold start-up to stable operation: Numerical model and experimental results

    Feng, Huihua   Guo, Chendong   Jia, Boru   Zuo, Zhengxing   Guo, Yuyao   Roskilly, Tony  

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  • Systematic Reduction of the Detailed Kinetic Mechanism for the Combustion of n-Butane

    Liu, Chunhui   Zuo, Zhengxing   Feng, Huihua  

    A systematic approach for mechanism reduction was demonstrated to generate a skeletal and reduced mechanism for the oxidation of n-butane. First, a skeletal mechanism, including 89 species and 440 elementary reactions, was derived from a 230-species detailed mechanism using path flux analysis (PFA). Then, the unimportant reactions were eliminated using the importance index defined in computational singular perturbation (CSP), resulting in a skeletal mechanism consisting of 89 species and 298 elementary reactions. Finally, 20 global quasi-steady-state species were identified using a CSP-based time-scale analysis, leading to a 69-species reduced mechanism. Validation of the 89-species skeletal and 69-species reduced mechanisms showed good agreement with the detailed mechanism for both the ignition delay time and the distribution of species concentration over a wide range of simulation conditions.
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  • Influence of Material Parameters and Thermal Parameters on Sealing Performance of Reactor Pressure Vessel Under Heat Focusing Effect

    Tian, Jingyi   Feng, Huihua   Yang, Ye   Liang, Junming   Kuang, Yuxiao   Zhang, Huiyong  

    In this paper, an effective numerical model is established by combining the fluid-structure coupling and thermomechanical coupling methods to solve complex sealing problems of a reactor pressure vessel (RPV) test simulator under heat focusing effect. Some key factors are considered in the structure and thermal analysis, such as contact nonlinearity, high temperature elastic-plastic, and high temperature compression-resilience performance. The simulation results agree well with the data of test. An analysis is performed to study the effects of material and thermal parameters on sealing performance. The stress and deformation mechanism of bolt flange and gasket connection system is clarified.
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  • Review of recent advances of free-piston internal combustion engine linear generator

    Guo, Chendong   Zuo, Zhengxing   Feng, Huihua   Jia, Boru   Roskilly, Tony  

    Free piston internal combustion engine linear generator (FPELG) is a novel energy conversion device. Compared with traditional rotary internal combustion engines, FPELG shows many potential advantages due to the elimination of crank-connecting rod mechanism, such as structure simply, the high thermal efficiency, the low emission, the multi-fuel and the multi combustion mode feasibility. Therefore, the FPELG has become a research hot-point in recent years and has achieved a lot of research results. This paper mainly discusses and summarizes the recent technical advances of the FPELG from the research groups worldwide. After a brief introduction on the early research of the free-piston internal combustion engines, its working principle and different configurations are introduced respectively. Then, this paper mainly focuses on the recent research progress of the FPELG from the aspects of modeling and simulation method, experimental approach, and control strategies development. In the end of the paper, the research trend and future development of the FPELG will be prospected. It is concluded that matching and optimizing performances of free-piston internal combustion engine and linear generator are the key research points, and the controlled piston trajectory of the FPELG is the key technology.
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  • Trapping devices of nematode-trapping fungi:formation,evolution,and genomic perspectives

    Su, Hao   Zhao, Yong   Zhou, Jing   Feng, Huihua   Jiang, Dewei   Zhang, Ke-Qin   Yang, Jinkui  

    Nematode-trapping fungi (NTF) are potential biological control agents against plant-and animal-parasitic nematodes. These fungi produce diverse trapping devices (traps) to capture, kill, and digest nematodes as food sources. Most NTF can live as both saprophytes and parasites. Traps are not only the weapons that NTF use to capture and infect nematodes, but also an important indicator of their switch from a saprophytic to a predacious lifestyle. Formation of traps and their numbers are closely related to the nematicidal activity of NTF, so the mechanisms governing trap formation have become a focus of research on NTF. Recently, much progress has been made in our understanding of trap formation, evolution, and the genome, proteome and transcriptome of NTF. Here we provide a comprehensive overview of recent advances in research on traps of NTF. Various inducers of trap formation, trap development, structural properties and evolution of traps are summarized and discussed. We specifically discuss the latest studies of NTF based on genomic, proteomic and transcriptomic analyses.
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  • Evaluation and Improvement of the Sound Quality of a Diesel Engine Based on Tests and Simulations

    Yang, Zhengwei   Feng, Huihua   Ma, Bingjie   Khalifa, Ammar Abdualrahim Alnor  

    Traditional acoustic evaluation of a diesel engine generally uses the A-weighted sound pressure level (AWSPL) and radiated sound power to assess the noise of an engine prototype present in an experiment. However, this cannot accurately and comprehensively reflect the auditory senses of human subjects during the simulation stage. To overcome such shortage, the Moore-Glasberg loudness and sharpness approach is applied to evaluate and improve the sound quality (SQ) of a 16 V-type marine diesel engine, and synthesizing noise audio files. Through finite element (FE) simulations, the modes of the engine's block and the average vibrational velocity of the entire engine surface were calculated and compared with the test results. By further applying an automatically matched layer (AML) approach, the engine-radiated sound pressure level (SPL) and sound power contributions of all engine parts were obtained. By analyzing the Moore-Glasberg loudness and sharpness characteristics of three critical sound field points, an improvement strategy of the oil sump was then proposed. After improvement, both the loudness and sharpness decreased significantly. To verify the objective SQ evaluation results, ten noise audio clips of the diesel engine were then synthesized and tested. The subjective evaluation results were in accordance with the simulated analysis. Therefore, the proposed approach to analyze and improve the SQ of a diesel engine is reliable and effective.
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  • Multi-dimensional scavenging analysis of a free-piston linear alternator based on numerical simulation

    Mao, Jinlong   Zuo, Zhengxing   Li, Wen   Feng, Huihua  

    A free-piston linear alternator (FPLA) is being developed by the Beijing Institute of Technology to improve the thermal efficiency relative to conventional crank-driven engines. A two-stroke scavenging process recharges the engine and is crucial to realizing the continuous operation of a free-piston engine. In order to study the FPLA scavenging process, the scavenging system was configured using computational fluid dynamics. As the piston dynamics of the FPLA are different to conventional crank-driven two-stroke engines, a time-based numerical simulation program was built using Matlab to define the piston's motion profiles. A wide range of design and operating options were investigated including effective stroke length, valve overlapping distance, operating frequency and charging pressure to find out their effects on the scavenging performance. The results indicate that a combination of high effective stroke length to bore ratio and long valve overlapping distance with a low supercharging pressure has the potential to achieve high scavenging and trapping efficiencies with low short-circuiting losses. (C) 2010 Elsevier Ltd. All rights reserved.
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  • In-cylinder heat transfer and gas motion of a free-piston diesel engine generator

    Yuan, Chenheng   Xu, Jing   Feng, Huihua  

    The free-piston engine generator is an attractive alternative to the conventional reciprocating engine due to the feature that it moves without crankshaft system. This paper presented a simulation for the investigation on the characteristic of in-cylinder gas motion and heat transfer in a compression ignited free-piston engine generator. An operation experiment was performed to obtain the precise piston motion for the modeling of heat transfer and gas flow. The development of the multi-dimensional model was described, and simulation results were presented and showed good similarity with the experimental data. Then, the heat transfer and gas motion in the free-piston engine generator were discussed, on which the influences of piston motion were also investigated compared with a corresponding conventional reciprocating engine. The results indicated that compared with the conventional reciprocating engine, a higher level of squish and reverse squish effect was found for the free-piston engine generator due to its faster motion around top dead center, while its slower piston motion led to weaker gas turbulence in the compression process. Moreover, the free-piston engine generator and conventional reciprocating engine did not show a significant difference in heat transfer during the compression process, however, an obvious advantage of heat transfer was indicated for the free-piston engine generator in combustion and expansion processes due to its lower combustion temperature and the reduced time that is available for heat transfer caused by its faster expansion. The mechanism for such differences is that the free-piston engine generator moves with uneven equivalent speed.
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  • A Decoupled Design Parameter Analysis for Free-Piston Engine Generators

    Jia, Boru   Zuo, Zhengxing   Smallbone, Andrew   Feng, Huihua   Roskilly, Anthony Paul  

    The free-piston engine generator (FPEG) is a novel power generation device with an estimated brake efficiency (energy contained in the fuel that is transformed into useful work) of up to 46%, compared to the 25-35% reported in conventional reciprocating engines. This paper seeks to address a major challenge in the development of new and complex technologies-how do we effectively communicate and understand the influence of key design parameters on its operating performance? In this paper, the FPEG is described using a simple numerical model, a model which is reduced to a forced mass-spring vibration system under external excitation, enabling all the major input parameters to be decoupled. It proved that the engine piston position as a function of time and output power could be predicted directly from the input parameters with acceptable accuracy. The influence of the key FPEG design parameters on the piston oscillation characteristics and electric power output can be characterised with respect to one another and summarised. Key design parameters include piston mass, compression stroke length, piston cross sectional area, and electric load. Compared with previous and more complex numerical models, the presented methods can be used to simply describe the sensitivity of key design parameters on the FPEG performance. It will provide useful general guidance for the FPEG hardware design process.
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  • Effect of closed-loop controlled resonance based mechanism to start free piston engine generator:Simulation and test results

    Jia, Boru   Zuo, Zhengxing   Feng, Huihua   Tian, Guohong   Smallbone, Andrew   Roskilly, A. P.  

    Two general methods to start the engine are investigated by the linear electric machine operating as a linear motor and identified one for a specific FPEG prototype configuration. Based on that, a novel method to start the engine by mechanical resonance is proposed. Both simulation and test results are presented, and the numerical model is successfully validated. The results show that with a fixed motor force of 110 N, within 0.5 s, the maximum in-cylinder pressure could reach 13 bar, indicating that the engine is ready for ignition. Further investigation on the engine performance with the closed-loop control strategy is carried out. The results demonstrate that it is feasible to start the FPEG with mechanical resonance with a closed-loop controlled electric linear machine that applies a proper constant motor force in the direction of the natural bouncing motion. With different starting motor force, the top dead centre (TDC) value for both cylinder is different during the first few running cycles, but the difference reduces and tends to be zero during the stable resonance state. There is not any significant difference observed on the engine frequency and piston profile during combustion process. (C) 2015 Elsevier Ltd. All rights reserved.
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  • Higher order accuracy analysis of the second-order normal form method

    Xin, Zhenfang   Zuo, Zhengxing   Feng, Huihua   Wagg, David   Neild, Simon  

    The second-order normal form method has shown its intelligence in handling the weak nonlinear vibration problems, especially the lightly damped nonlinearities. The new technology can directly realize near identify transformation to the differential equation, while the first-order method has to change the differential equation to the first-order form at the very beginning. In order to get a more precise result, a lot of effort has been done to realize it through eliminating unnecessary approximations or reconsidering the influence of the nonlinearity in the subsequent processing. It is easy to conduct a simplified nonlinear transformation to get the first-order motion equation. Here in this paper, we focus on the higher-order accurate terms in the dynamic equation. The Taylor series expansion and the Poincar, expansion of the nonlinearity indicate that there are other resonance terms existing in final dynamic equation. A general form of expression for higher-order resonance response function has been derived. The results show that the additional resonance terms cannot obviously increase the accuracy of the second-order normal form method; also, it cannot improve much of the predictions of sub and superharmonic responses.
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  • Disturbance analysis of a free-piston engine generator using a validated fast-response numerical model

    Jia, Boru   Smallbone, Andrew   Mikalsen, Rikard   Feng, Huihua   Zuo, Zhengxing   Roskilly, Anthony Paul  

    In this paper, a fast-response numerical model was used to investigate potential disturbances to a free piston engine generator (FPEG), i.e. engine cycle-to-cycle variations, misfire and immediate electric load change. During the engine operation, there could be one disturbance taking place or several disturbances take place simultaneously. By identifying different types of system disturbance with specific occurring times, the influence on the system was characterised. It was found that a step change of electric load would induce a corresponding top dead centre (TDC) step change. Low variations on piston TDC are observed when cycle-to-cycle variations take place. When unsuccessful ignition occurs, the engine will stop after one oscillation cycle. Reducing the electric load after misfire would cause more oscillation cycles and require a restart of the engine. Technically feasible control variables were identified and coupled with a PI feedback controller design to minimise the impact of each kind of disturbance, a design which could be used in future FPE control system designs. The controller performance was seen to be satisfactory for the electric load step change, and the piston TDC was controlled to back to the set point in 0.5 s. (C) 2016 The Authors. Published by Elsevier Ltd.
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  • Parameters coupling designation of diesel free-piston linear alternator

    Mao, Jinlong   Zuo, Zhengxing   Feng, Huihua  

    This research presents a novel parameters coupling designation method of diesel free-piston linear alternator. The relationship between the main parameters of linear alternator and free-piston engine is built up based on the energy conservation relationship between these two devices. An iterative procedure is carried out among the zero-dimensional numerical simulation of the free-piston linear alternator, CFD calculation of the gas exchanging process and combustion process of the free-piston engine to define the main geometric dimensions of the free-piston engine. A starting method of using the resonance characteristics of free-piston engine is simulated with different relatively small constant thrust forces and the designed free-piston engine could be started by the linear alternator. The results indicate that the load of the linear alternator is primarily associated with the bore of the engine, and the maximum electromagnetic force is approximately proportional to the square of the bore; the effective stroke length is associated with the optimum working point of free-piston linear alternator which could be defined using the numerical simulation program. (C) 2011 Elsevier Ltd. All rights reserved.
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