耦合全工况高效余热回收系统的混动卡车道路适应性研究

公路运输领域的节能减排是实现碳中和战略的重要环节。重型商用车辆功率以及续航需求大,由传统燃油车型向混合动力转型并进行余热回收利用对提升发动机效率、降低能耗具有重要意义。但目前的研究中与混合动力耦合的余热回收系统的结构简单,仅能回收缸套水或烟气单一形式的余热能,对车辆整体效率的提升程度有限。因此提出了一种基于有机朗肯循环的能够同时回收烟气及缸套水余热并在全工况下高效运行的余热回收系统。将其与串联式混合动力系统耦合,并在高速、城郊道路工况下运行,深入探究了有机朗肯循环系统性能表现以及耦合系统整体能效提升效果。结果表明在考虑余热回收系统质量的前提下,该余热回收系统在高速路况USHWY对发动机效率的提升为2.85%,降低整体燃油消耗6.78%,在城郊路况UDDS下提升发动机效率2.30%,整体燃油消耗降低6.43%,证明了系统的节油能力和应用潜力。研究发现有机朗肯循环系统工作惯性大,发动机的长期稳定运行对于提升系统输出功率和效率具有决定性作用,因此该系统适合匹配高速运行的重型混合动力车辆。

基于深度强化学习的有机朗肯循环内燃机余热回收系统瞬态优化控制

有机朗肯循环因其热效率较高、部件成熟的优点,被认为是目前主流的内燃机余热回收技术。然而由于实际道路工况的复杂多变,给余热回收系统在瞬变工况下的安全高效控制带来了巨大挑战。为此,该文提出基于深度强化学习的控制方法,通过线下学习优化控制结合线上做决策解决此问题。建立经过实验验证的跨临界有机朗肯循环动态仿真模型,作为深度强化学习的训练环境,进而学习到安全的优化控制策略。仿真结果表明:深度强化学习控制器相比于传统PID恒温控制器(控制膨胀机进口工质温度为定值),可将系统始终控制在更安全和高效的状态;且在未经训练的瞬态波动热源条件下,深度强化学习控制器表现出了较好的外推泛化性能。研究结果证明深度强化学习对瞬态工况下的热动力循环优化控制具有非常可观的潜力。

机理骨架结合表征参数的换热器建模方法研究

间壁式换热器广泛应用于能源动力系统中,并对整个系统的稳态和动态性能都有至关重要的影响作用,因此建立准确的动态仿真模型至关重要。目前,针对间壁式换热器的动态仿真模型主要有两大类即基于机理和基于辨识的模型。针对机理建模方法计算速度较慢,并需要实验数据标定保证精度的缺点,以及模型辨识技术不可解释,适用性和稳定性差的缺点,该文提出使用最基本的机理作为模型骨架奠定模型稳定性并减少模型计算量,同时推导出具有物理意义的表征参数来保证模型精度,并使用深度强化学习算法来获得参数的准确值。该文将方法称之为机理骨架结合表征参数的建模方法,其中机理骨架比拟事物的基本框架特征,表征参数比拟事物的表象特征。基于此,通过对一个有机朗肯循环中蒸发器的建模,将建模方法和基于机理的建模方法做了对比。对比结果证明所提出的建模方法与机理建模方法具有等价性,同时还可以显著提高计算速度;而相比于模型辨识方法,该方法具有可解释性,以及很好的稳定适用性。

不同工质的有机朗肯循环系统变工况特性对比研究

针对分布式能源系统中内燃机负荷变化较大、传统的有机朗肯循环(ORC)工质优选未能关注变工况性能的问题,开展了基于变工况特性的ORC工质优选研究。首先,基于MATLAB平台构建了基于变工况特性的工质优选模型,涉及系统设计参数获取、变工况仿真和热经济性分析3个层面,具有较高的模型精度。然后,基于该模型,针对8种典型实用性工质,分析了变工况循环性能及典型全日电负荷下的热经济性能。研究表明:水在高负荷工况时的净输出功率较多,适合运行在高负荷工况条件下,而甲苯在低负荷工况时展现出较大的性能优势,适合运行在低负荷工况条件下;在考虑实际运行情况下,水的发电成本和折旧回收期为0.131美元·(kW·h)^(-1)和8.08a,而甲苯的分别为0.127美元·(kW·h)^(-1)和6.75a。这些规律进一步表明,水适用于电负荷稳定的建筑类型,而甲苯适用于电负荷瞬变的建筑类型。

基于运行工况传递路径分析和串扰消除的车内噪声分离技术研究

为有效避免运行工况传递路径分析在进行匀速工况噪声源分离时,轮胎附近测得振动噪声容易受到发动机振动噪声的干扰,导致分离结果不准确的问题,结合串扰消除方法开展了相关研究。建立了运行工况传递路径分析模型,针对某车型的匀速问题,将运行工况传递路径分析方法与串扰消除技术相结合,通过三级细化实现匀速车内噪声的精准划分和声源目标值设定,实现了匀速车内噪声的逐层控制。

气体机排气驱动吸收式制冷机变工况调节特性

以内燃机为原动机的分布式供能系统中,发动机工况变化对吸收式制冷机运行具有重要影响.建立了某发电用气体机排气驱动的吸收式制冷系统稳态模型,提出了"动态多种群粒子群优化(DMS-PSO)+NM单纯形法"复合算法对模型进行求解.依据气体机实测余热数据,研究了发动机不同工况下调节溶液循环量对系统性能的影响.结果表明,以额定溶液循环量运行时,当发动机负荷低于30%,时,余热制冷系统由于循环倍率过大而无法正常运行.通过减小溶液循环量可以显著改善发动机低负荷时的系统性能,发动机负荷为40%,时,系统制冷量提升26.9%,.由于溶液结晶限制,在发动机不同负荷下,溶液循环量调节存在最低限值.

内燃机余热回收ORC系统三层次评价方法

针对内燃机余热回收ORC系统评价优选的不完善性,在综合考虑安全环保可靠性、热力学性能、技术经济性及节能减排效益这三层级属性因素基础上,提出了一种结合多级非结构模糊决策的三层次评价方法:评价模型建立、系统优化和评价决策.根据提出的方法,建立了用于某柴油机排气余热回收的简单循环和回热循环系统模型,对这两系统分别采用7种工质的14个方案进行了优化与评价决策.结果表明:回热循环较简单循环系统有较优异的综合性能;考虑不同层级因素时方案间的优劣排序会产生变化.验证了此评价优选方法的可行性,可拓展应用于内燃机多余热源回收采用不同结构、循环方式和工质的ORC系统优选.

热再生氨基液流电池电堆模型建立及性能分析

由多电堆组成的液流电池系统通常用于大规模电能存储应用.在这种多电堆系统中,不可避免地存在与管道系统中电解液流动相关的传输延时,这会对系统设计和运行性能产生重要影响.针对热再生氨基液流电池电堆系统,设计开发了一个包含传输延时的动态模型,研究了不同系统设计和运行条件对系统性能的影响.仿真结果表明:传输延时会导致电解液浓度在管道中分布不均匀,并导致系统中的电堆电压均匀性较差.探究了电堆在不同流量、不同管道尺寸和不同反应物浓度下的运行情况,电堆输出功率随着流量的增大呈现先增加后减小的变化趋势,而整个系统的压降随着流量的增大而增加,当考虑到整个系统的压降损失时,电堆的总功率与电堆的输出功率呈相同的变化趋势;并且流量的增加会使反应物的浓度分布和电堆电压更加均匀.电堆输出功率随着管道半径的增加而增大,随着管道长度的增加呈现先增加后减小的趋势,考虑压降损失后的总功率也与输出功率呈现相同的变化趋势.电解液反应物浓度(Cu^(2+)、Cu(NH_(3))^(2+)_(4)、NH_(3))的变化也会影响电堆的输出功率,电堆的输出功率随着NH3初始浓度的增加而增大;而对于Cu^(2+)来说,存在一个最佳浓度值,使得电堆输出功率最大;随着Cu(NH_(3))^(2+)_(4)浓度的增加,电堆功率会逐渐降低.

快速压缩机缸内温度不均匀性及其对自燃的影响

快速压缩机中活塞运动产生涡流会导致缸内温度分布不均匀,并对自燃时刻产生显著影响.针对这一问题,对不同活塞缝隙下缸内温度不均匀性及其对自燃时刻的影响进行了研究.首先,建立了Fluent网格模型并耦合氢气详细化学反应机理,研究了无缝隙活塞缸内温度场及自燃过程;然后,对不同活塞缝隙结构进行缸内温度场的数值模拟,确定最佳活塞缝隙结构;最后,对比了基于CHEMKIN、Livengood-Wu积分以及Fluent 3种方法获得的自燃时刻.结果表明:无缝隙活塞缸内未受涡流影响区域先发生自燃,并引发明显火焰传播.体积为原燃烧室体积9.5%,左右的活塞缝隙能很好抑制涡流产生.Livengood-Wu积分在预测快速压缩机缸内气体,尤其是缸内受涡流影响区域气体的自燃时刻时具有较高的准确性.

涡旋膨胀机润滑系统设计及输出性能实验研究

为了研究涡旋膨胀机输出性能规律,将某商用涡旋压缩机改造成涡旋膨胀机,并对其润滑系统进行了设计和精确控制;基于此,搭建了以压缩空气作为工质的测试实验台,对比了膨胀机在有无润滑条件下的性能,并对膨胀机的性能进行了全面的测试。结果表明:润滑系统在机械润滑和膨胀机性能方面都起到良好的效果;在实验工况范围内,膨胀机等熵效率均保持在40%以上,最高等熵效率为54.45%,输出电功率达到了753 W;负载数量一定时,膨胀机输出功率随空气流量的增加而增加,但等熵效率随流量的增大而减小;在不同的负载数量下,受到机械磨损和内部泄漏的影响,等熵效率均随着膨胀机转速的增加先增大后减小,存在最优等熵效率转速区间为2800~3200 r/min;而当转速一定时,膨胀机的输出功率取决于进口压力的大小;随负载的增加,膨胀机的输出功率和进口压力成相似的增长趋势。研究结果可为有机朗肯循环系统优化提供参考。

Calculation on Cylinder Pressure Fluctuation by Using the Wave Equation in KIVA Program

Cylinder pressure fluctuation during combustion process of internal combustion engine is closely related to combustion noise and knock.The current studies are based on cylinder pressure test to obtain information on combustion noise and knock,but there is little for simulation of combustion pressure fluctuation.Based on effects of combustion process in the combustion chamber on cylinder pressure by using wave equation,the mechanism of pressure fluctuation during combustion is researched with three-dimensional acoustic wave equation and flow field model of KIVA program.The cylinder pressure fluctuation curve,temperature field and acoustic field are obtained from the coupled calculation of the wave equation and KIVA program.The frequency spectrum analysis is taken with the cylinder pressure oscillation of cylinder pressure measured and calculated.The calculation result is consistent with the experimental result.This indicates that the cylinder pressure fluctuation can be correctly calculated with the wave equation.Analysis of calculation results of temperature field and acoustic field shows that sound field changes faster than flame propagates,and distribution of sound field is more complicated.Combustion pressure oscillation in the diesel engine is under highly unstable condition.This indicates that the combination of cylinder pressure fluctuation model and combustion model is an effective method to study the pressure oscillations and a new method to study the combustion noise and knock.

Identification of Axial Vibration Excitation Source in Vehicle Engine Crankshafts Using an Auto-regressive and Moving Average Model

Violent axial vibration of a vehicle engine crankshaft might lead to multiple defects to the engine.Much research on mechanism and control measures has been done on engines,such as using the dynamic stiffness matrix method,rayleigh differential method,and system matrix method.But the source of axial vibration has not been identified clearly because there are many excitation factors for the axial vibration of a crankshaft,such as coupled torsional-axial vibration and coupled bending-axial vibration,etc.In order to improve the calculation reliability and identify the excitation source of axial vibration of in vehicle engine crankshafts,this paper presents a method to identify the axial vibration excitation source of crankshafts for high speed diesel engines based on an auto-regressive and moving average（ARMA） model.Through determining initial moving average variables and measuring axial /bending/torsional vibrations of a crankshaft at the free-end of a 4-cylinder diesel engine,autoregressive spectrum analysis is applied to the measured vibration signal.The results show that the axial vibration of the crankshaft is mainly excited by coupled bending vibration at high speed.But at low speed,the axial vibration in some frequencies is excited primarily by torsional excitation.Through investigation of axial vibration source of engine crankshafts,calculation accuracy of vibration can be improved significantly.

Simulation Research on the Effect of Cooled EGR, Supercharging and Compression Ratio on Downsized SI Engine Knock

Knock in spark-ignition（SI） engines severely limits engine performance and thermal efficiency. The researches on knock of downsized SI engine have mainly focused on structural design, performance optimization and advanced combustion modes, however there is little for simulation study on the effect of cooled exhaust gas recirculation（EGR） combined with downsizing technologies on SI engine performance. On the basis of mean pressure and oscillating pressure during combustion process, the effect of different levels of cooled EGR ratio, supercharging and compression ratio on engine dynamic and knock characteristic is researched with three- dimensional KIVA-3V program coupled with pressure wave equation. The cylinder pressure, combustion temperature, ignition delay timing, combustion duration, maximum mean pressure, and maximum oscillating pressure at different initial conditions are discussed and analyzed to investigate potential approaches to inhibiting engine knock while improving power output. The calculation results of the effect of just cooled EGR on knock characteristic show that appropriate levels of cooled EGR ratio can effectively suppress cylinder high-frequency pressure oscillations without obvious decrease in mean pressure. Analysis of the synergistic effect of cooled EGR, supercharging and compression ratio on knock characteristic indicates that under the condition of high supercharging and compression ratio, several times more cooled EGR ratio than that under the original condition is necessarily utilized to suppress knock occurrence effectively. The proposed method of synergistic effect of cooled EGR and downsizing technologies on knock characteristic, analyzed from the aspects of mean pressure and oscillating pressure, is an effective way to study downsized SI engine knock and provides knock inhibition approaches in practical engineering.

基于PC-SAFT的CO_(2)混合工质相平衡计算

统计缔合流体理论(PC-SAFT)能够应用于CO_(2)动力循环中CO_(2)混合工质物性的预测。PC-SAFT状态方程在计算CO_(2)混合工质气液相平衡时,其收敛性较差。本文介绍一种利用基于基团贡献法的蒸气压估算方法为PC-SAFT状态方程提供初值,从基团角度来预测CO_(2)混合工质气液平衡的方法。该方法在很多情况下的准确度高于Refprop 9.0计算结果,尤其在较高的CO_(2)比例下。对于温度滑移较大的CO_(2)混合工质计算中,该方法不会计算出Refprop 9.0中不平滑的尖点,避免了在一些情况下出现反常的计算结果,是一种稳定可靠的计算方法。

组分可调的冷电联合循环性能分析

针对并联型冷电联合循环混合工质充注组分无法同时匹配两子循环的问题,基于循环拆分法对其进行剖析,根据拆分所得子循环的性能变化规律,提出了组分调控方法以实现组分和子循环的匹配,并设计了一个理想的组分可调的冷电联合循环系统。计算结果表明,当工质的两相冷凝温度滑移小于冷凝水温升时,适当的过冷可以提高冷凝段的温度匹配,提高循环性能。但受限于调控形式,本文所提出的调控方法仅在较大冷凝水温升和较高制冷量情况下,才能实现冷电联合循环性能的显著提升。

外部参数扰动下CO_(2)冷电联合循环运行性能研究

二氧化碳是优良的发电循环工质和制冷剂,通过二氧化碳冷电联合循环可实现电能和冷能并供,目前已有一些循环理论探索与分析,未见实验研究。为此,本文搭建了一套基于二氧化碳工质的冷电联合循环试验样机系统并开展了初步实验测试。结果表明,在动力子循环运行稳定后启动制冷子循环,系统关键运行参数仅在小幅度范围内发生变化,联合循环能平稳快速地实现从动力循环模式向冷电联合循环模式的切换。此外,本文探究了外部冷热源参数变化下循环系统的运行及性能响应规律,可为进一步优化二氧化碳冷电联合循环的结构和系统设计提供参考。

Analysis of an electricity-cooling cogeneration system for waste heat recovery of gaseous fuel engines

Waste heat recovery(WHR)is one of the most useful ways to improve the efficiency of internal combustion engines,and an electricity-cooling cogeneration system(ECCS)based on Rankin-absorption refrigeration combined cycle for the WHR of gaseous fuel engines is proposed in the paper.This system can avoid wasting the heat in condenser so that the efficiency of the whole WHR system improves,but the condensing temperature of Rankin cycle(RC)must increase in order to use absorption refrigeration system,which leads to the decrease of RC output power.Therefore,the relationship between the profit of absorption refrigeration system and the loss of RC in this combined system is the mainly studied content in the paper.Because the energy quality of cooling and electricity are different,cooling power in absorption refrigeration is converted to corresponding electrical power consumed by electric cooling system,which is defined as equivalent electrical power.With this method,the effects of some important operation parameters on the performance of the ECCS are researched,and the equivalent efficiency,exergy efficiency and primary energy rate are compared in the paper.

Energy management strategy for hybrid electric vehicle integrated with waste heat recovery system based on deep reinforcement learning

Hybrid electric vehicles(HEVs)are acknowledged to be an effective way to improve the efficiency of internal combustion engines(ICEs)and reduce fuel consumption.Although the ICE in an HEV can maintain high efficiency during driving,its thermal efficiency is approximately 40%,and the rest of the fuel energy is discharged through different kinds of waste heat.Therefore,it is important to recover the engine waste heat.Because of the great waste heat recovery performance of the organic Rankine cycle(ORC),an HEV integrated with an ORC(HEV-ORC)has been proposed.However,the addition of ORC creates a stiff and multi-energy problem,greatly increasing the complexity of the energy management system(EMS).Considering the great potential of deep reinforcement learning(DRL)for solving complex control problems,this work proposes a DRL-based EMS for an HEV-ORC.The simulation results demonstrate that the DRL-based EMS can save 2%more fuel energy than the rule-based EMS because the former provides higher average efficiencies for both engine and motor,as well as more stable ORC power and battery state.Furthermore,the battery always has sufficient capacity to store the ORC power.Consequently,DRL showed great potential for solving complex energy management problems.

Experimental investigation on diesel engine's waste heat capacity under mapping characteristics

Waste heat recovery for internal combustion engine(ICE)has been considered as an important strategy to improve efficiency and promote fuel economy,thus alleviating the problems of energy shortage and environmental pollution.This paper investigates the characteristics of various kinds of waste heat energy,namely,waste heat in exhaust,cooling water and charge air,over the engine’s whole operating region.Based on the energy balance experiments,the energy distribution of a conventional heavy-duty diesel engine is obtained under mapping characteristics.According to exergy analysis,the energy recovery potential for waste heat is studied as well.The experimental results indicate that exhaust energy increases with engine speed and load,while cooling water energy is more sensitive to load,especially at low and middle speed.Charge air energy,on the other hand,mainly counts on speed rather than load.Exhaust energy possesses the highest recovery potential in terms of both quantity and quality.Through waste heat recovery,a dramatic improvement in engine efficiency is achievable,actually,the maximum value can amount to 60%or even more.

Carbon Dioxide as Working Fluids in Transcritical Rankine Cycle for Diesel Engine Multiple Waste Heat Recovery in Comparison to Hydrocarbons

In consideration of the high-temperature characteristic of engine's waste heat and stricter environmental regulations, natural substance, including CO_2 and hydrocarbons, have been treated as promising working fluid for diesel engine waste heat recovery due to its environment friendly and excellent physical and chemical properties. This paper presented a comprehensive performance analysis on transcritical Rankine cycles for diesel engine multiple waste heat recovery using hydrocarbons and CO_2 as working fluid. The optimal turbine inlet pressures corresponding to maximum net power output, maximum exergy efficiency and minimum electricity production cost(EPC) were obtained. The effect of working fluid on these optimal pressures has been discussed. For fluids with low critical temperature, the optimal pressure corresponding to maximum net power output is lower than the one for maximum exergy efficiency, while the opposite results can be found for fluid with high critical temperature. Then, the effect of various working fluid properties in transcritical cycle performance is discussed. Comparison results show that CO_2 obtains only more power output than Ethane, Propane and Propene, but CO_2 is capable of absorbing more energy from engine coolant and regeneration heat with comparable total heat transfer areas and has an advantage in turbine size, particularly for hydrocarbons with high critical temperature.