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Jiang J.,Xian Jiaotong University | Wu Z.,Tianjin University | Wu Z.,State Key Laboratory of Engines
International Journal of Bifurcation and Chaos | Year: 2010

In this paper, the linear and nonlinear modes of the unforced coupled rotor/stator system from a general rotor/stator model, which accounts for both the dynamics of the rotor and the stator as well as the friction and the deformation at the contact surfaces, are derived. The bifurcations of the nonlinear normal modes are analyzed based on the constrained bifurcation theory with the linear normal modes as the constraints. Then, the existence boundaries and the backward whirl frequencies of dry friction backward whirl a hazardous self-excited oscillation in rotor/stator systems of this model are derived. It is found by analysis that many inherent characteristics of the dry friction backward whirl can be derived from the information of the interaction of the linear and the nonlinear normal modes of the coupled rotor/stator system, such as the number of existence regions and their position relationship, the minimal friction on the contact surfaces that may induce the self-excited oscillation, the upper limits of the backward whirl frequencies of the response, and more. This study has well demonstrated the dominant role of the interaction of the linear and the nonlinear normal modes in deciding the characteristics of some nonlinear dynamical behaviors. © 2010 World Scientific Publishing Company. Source

Tian H.,Tianjin University | Shu G.-Q.,State Key Laboratory of Engines | Wei H.Q.,State Key Laboratory of Engines | Liang X.,State Key Laboratory of Engines | Yu G.,State Key Laboratory of Engines
SAE International Journal of Engines | Year: 2013

A novel combined power and cooling cycle based on the Organic Rankine Cycle (ORC) and the Compression Refrigeration Cycle (CRC) is proposed. The cycle can be driven by the exhaust heat form a diesel engine. In this combined cycle, ORC will translate the exhaust heat into power, and drive the compressor of CRC. The prime advantage of the combined cycle is that both the ORC and CRC are trans-critical cycles, and using CO2 as working fluid. Natural, cheap, environmentally friendly, nontoxic and good heat transfer properties are some advantages of CO2 as working fluid. In this paper, besides the basic combined cycle (ORC-CRC), another three novel cycles: ORC-CRC with an expander (ORC-CRCE), ORC with an internal heat exchanger as heat accumulator combined with CRC (ORCI-CRC), ORCI-CRCE, are analyzed and compared. The cycle parameters, including the coefficient of performance (cop), the cooling capacity (Qro) and expansion power of CRC (We) have been analyzed and optimized as the variation of the high pressure of ORC, the high pressure and the outlet temperature of gas cooler of CRC, and temperature drop of heat source in heat accumulator of ORC. The results indicate that there is an optimal high pressure of CRC (about 8.6MPa to 8.8MPa) for the combined cycles, at which the combined cycles achieve the optimal performance. The results also show that both the expander and heat accumulator could improve the system performance. The higher ΔTi could improve the system performance, but also resulting the more insufficiency of waste heat recovery. © 2013 SAE International. Source

Shu G.-Q.,State Key Laboratory of Engines | Yu G.,State Key Laboratory of Engines | Tian H.,State Key Laboratory of Engines | Wei H.,State Key Laboratory of Engines | Liang X.,Tianjin University
SAE Technical Papers | Year: 2013

A bottoming waste-heat-recovery (WHR) model based on the Organic Rankine Cycle (ORC) is proposed to recover waste heat from exhaust gas and jacket water of a typical diesel engine (DE). The ORC model is detailed built based upon real structural and functional parameters of each component, and is able to precisely reflect the working process of the experimental ORC system constructed in lab. The DE is firstly tested to reveal its energy balance and the features of waste heat. The bottoming ORC is then simulated based on experimental data from the DE bench test using R245fa and R601a as working fluid. Thermodynamic evaluations are done on key parameters like waste heat recovered, expansion power, pump power loss and system efficiency. Results indicate that maximum expansion power and efficiency of the ORC are up to 18.8kW and 9.6%. Influences of engine condition, fluid mass flow and evaporating pressure on system performance are analyzed and meaningful regularities are revealed. The combined system of DE and bottoming ORC (DE-ORC) is also investigated. The results showed that the integration of the bottoming ORC greatly changed energy distribution of the DE, and the DE thermal efficiency is up to 47.2%, increasing by 9.0%. Copyright © 2013 SAE International. Source

Huang D.,Tianjin University | Xie H.,Tianjin University | Xiong S.,Tianjin University | Shen T.,Sophia University | And 2 more authors.
SAE Technical Papers | Year: 2016

The fuel economy of plug-in hybrid electric city bus (PHEV) is deeply affected by driving cycle and travel distance. To improve the adaption of energy management strategy, the equivalent coefficient of fuel is the key parameter that needs to be pre-optimized based on the predicted driving cycle. An iterative learning method was proposed and implemented in order to get the best equivalent coefficient based on the predicted driving cycle and battery capacity. In the iterative learning method, the energy model and kinematics model of the bus were built. The ECMS (Equivalent Consumption Minimization Strategy) method was applied to obtain the best fuel economy with the given equivalent coefficient. The driving paths and running time of city buses were relatively fixed comparing with other vehicles, and their driving cycle can be predicted by route content. The proposed optimized strategy was applied on the factory sets of plug-in hybrid electric city bus. In general case, energy management strategies of PHEV bus are often developed by several standard driving cycles, which are different with realistic driving condition. However, in this case, the energy management strategies were pre-optimized based on the future target application environment. The results indicate that the pre-optimized city bus can get better fuel economy and the profiles of battery SOC (State of charge) are well planned. The optimized strategy is also adequate for other types of PHEV vehicles, which are sensitive to driving cycle. © Copyright 2016 SAE International. Source

He W.,Tianjin University | He W.,State Key Laboratory of Engines | Wang S.,Tianjin University | Wang S.,State Key Laboratory of Engines | And 3 more authors.
Energy | Year: 2015

This paper presents an advanced mathematical model of a thermoelectric generator that includes the effect of the temperature gradient in the flow direction. The parameters of the exhaust gas from an engine may fluctuate during engine operation; thus, the influence of this fluctuation in the exhaust gas parameters on the optimal thermoelectric performance was considered with the objective of maximizing the total power output through the aid of Fortran. The optimum module areas corresponding to the maximum power output were found to be greatly affected by the flow rate of the exhaust gas but not by the gas temperature. The effect of the fluctuation in exhaust gas parameters on the performance of the corresponding thermoelectric generator at the maximum power output was also studied. A power deviation analysis method was introduced in order to design the optimal TEG module area for a high power output. Based on the results, the optimal design areas were 0.22 m2 for the co-flow and 0.3 m2 for the counterflow. The counterflow arrangement is recommended because it maintains a smaller deviation from the peak power output than a co-flow arrangement at their respective optimal design areas if there is sufficient system space. © 2015 Elsevier Ltd. Source

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