柴油机余热回收温差发电—有机朗肯联合循环变工况性能研究

发布时间：2018-08-18 13:26

【摘要】：节能和环保是汽车工业发展的两大主题。有关研究表明,发动机燃料燃烧所发出的能量只有三分之一左右被有效利用。回收利用这部分能量已经成为了提高内燃机效率重要的方式之一。其中,温差发电(TEG)技术具有可耐高温、无运动部件等优点,是适合柴油机排气余热这种中高温品位余热回收的技术手段;有机朗肯循环(ORC)具有运行稳定、效率高等特点,但是受限于工质的高温分解问题,适合于内燃机余热的回收中低温品位余热回收。柴油机变工况下排气温度较高且变化范围较大,可使用TEG系统预先对高温的排气进行回收,将排气温度降到有机工质适宜工作的范围,为ORC系统回收余热创造有利条件。因此,TEG和ORC的联合循环对柴油机变工况下的余热能进行回收是本文的研究重点。本文基于MATLAB建立了TEG与ORC联合系统的热力学模型,对某型柴油机开展了变工况余热回收的模拟研究。根据柴油机排气余热温度特性,TEG系统材料选择工作温度在300~600摄氏度范围的p型TAGS(碲锑锗银)/n型PbTe材料。ORC系统为带回热系统,可以进一步提升回收效率,系统有机工质为R123,其分解温度为600K。鉴于工况点较多,为使ORC系统在不同排气温度工况点下都可以稳定工作,且蒸发压力过大对系统稳定性有影响,所以选用较低蒸发压力以保证系统安全正常运行,故ORC系统朗肯循环状态为亚临界,工质蒸发压力为2MPa,冷凝温度为308K。分析结果表明,此联合系统基本可在柴油机全工况下运行。柴油机中高负荷时排气温度和流量相对较大,联合回收系统的输出功较高。联合系统在不同工况下的输出功最高可达30.36kW。其中TEG系统输出功为2.24kW,ORC系统输出功为28.12kW。发动机指示热效率最高可以提高5.52%,其指示热效率最高值为47.1%。联合系统在1700-1900r/min转速,70%-90%负荷这一工况范围下性能表现更好,若柴油机常在中高转速大负荷工况下运行,则使用此系统回收余热具有较大的经济价值。本文还设计并制作多模块串联的温差发电装置进行实验研究,探究了温差发电系统不同的冷热端温度下的伏安特性规律以及电流、输出功率关系。实验结果表明,冷端温度293K,热端温度473K时温差发电装置有最大输出功率39.648W。并使用此实验结果对TEG-ORC联合系统中TEG系统的理论模型进行了针对多模块串联后的修正,使其更能真实反映多模块串联后的温差发电系统回收余热的能力。此实验可以为联合系统模型修正优化以及TEG-ORC联合循环的实验研究进行前期的铺垫,有助于今后联合系统实验工作的开展。
[Abstract]:Energy saving and environmental protection are the two main themes of automobile industry development. Studies have shown that only about 1/3 of the energy emitted by engine fuel combustion is effectively utilized. Recycling this part of energy has become one of the most important ways to improve the efficiency of internal combustion engine. Among them, thermoelectric (TEG) technology has the advantages of high temperature resistance, no moving parts and so on. It is suitable for diesel engine exhaust heat recovery of medium and high temperature grade waste heat, organic Rankine cycle (ORC) has the characteristics of stable operation, high efficiency, etc. However, due to the high temperature decomposition of working fluid, it is suitable for the recovery of internal combustion engine waste heat. The exhaust temperature of diesel engine under different working conditions is higher and the range of variation is large. The exhaust temperature of high temperature can be recovered by using TEG system in advance, and the exhaust temperature can be reduced to the suitable working range of organic working medium, which will create favorable conditions for the recovery of residual heat in ORC system. Therefore, the combined cycle of TEG and ORC is the focus of this paper. In this paper, the thermodynamic model of TEG and ORC combined system is established based on MATLAB, and the simulation study of waste heat recovery in a diesel engine is carried out. According to the waste heat temperature characteristics of diesel engine exhaust gas, the material of TEG system can be selected as the back heat system of p type TAGS (Ag Te / n type PbTe system) with working temperature in the range of 600C, and the recovery efficiency can be further improved. The organic working fluid of the system is R123 and its decomposition temperature is 600K. In view of the large number of operating conditions, in order to make the ORC system work stably under different exhaust temperature conditions, and the excessive evaporation pressure has an effect on the stability of the system, the lower evaporation pressure is selected to ensure the safe and normal operation of the system. Therefore, the Rankine cycle state of ORC system is subcritical, the evaporation pressure of the working medium is 2 MPA, and the condensation temperature is 308 K. The analysis results show that the combined system can be operated in the whole working condition of diesel engine. The exhaust temperature and flow rate of the diesel engine are relatively large at medium and high loads, and the output power of the combined recovery system is higher. The output power of the combined system can reach 30.36 kW under different working conditions. The output power of TEG system is 2.24kW and 28.12kW. The maximum indicated thermal efficiency of the engine can be increased by 5.52 and the maximum indicated thermal efficiency is 47.1. The performance of the combined system is better in the range of 70% to 90% 1700-1900r/min speed. If the diesel engine is often operated under the conditions of medium and high speed and high load, it is of great economic value to use the system to recover the waste heat. This paper also designs and makes a multi-module thermoelectricity generator in series for experimental study, and probes into the law of volt-ampere characteristic and the relationship between current and output power of thermoelectric power generation system under different temperature of cold and hot end. The experimental results show that the maximum output power is 39.648W when the cold end temperature is 293K and the hot end temperature is 473K. Using the experimental results, the theoretical model of the TEG system in the TEG-ORC joint system is modified for the multi-module series-connected system, so that it can more truly reflect the ability of recovering the residual heat of the thermoelectric power generation system after the multi-module series-connected system. This experiment can pave the way for the experimental research of the joint system model modification and optimization and the TEG-ORC joint cycle, which is helpful to the joint system experiment in the future.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM913;TK115

【参考文献】