采用朗肯循环回收汽油机尾气余热的试验

发动机尾气能量占燃料燃烧放热总量的35%,左右,采用朗肯循环系统回收发动机尾气能量是实现汽车发动机节能的有效途径.针对一台2.0,L汽油机,搭建用于回收尾气余热的朗肯循环试验系统,探究了汽油机不同负荷下朗肯循环系统的性能,并得到单阀膨胀机的示功图.结果表明:单阀膨胀机转速和输出功率随汽油机负荷的增加而增大.汽油机在4,000,r/min、90%,负荷工况下,膨胀机转速达到1,640,r/min,输出功率达到3.47,k W,相当于汽油机功率的5.8%,.当汽油机在转速为5,500,r/min、功率为76.6,k W的工况下,膨胀机的最高压力可以达到6.69,MPa,通过测试示功图计算得到的单阀膨胀机的指示功率可以达到5.06,k W.     

车用柴油机-有机朗肯循环联合系统的设计及分析

针对一台车用柴油机全工况范围内排气能量的变化规律,设计了一套有机朗肯循环(organic Rankine cycle,ORC)余热回收系统,进而与车用柴油机耦合形成了车用柴油机-有机朗肯循环联合系统。ORC余热回收系统采用非共沸混合工质R416A,以高效回收柴油机的排气能量。采用螺杆膨胀机作为有机朗肯循环系统的动力输出部件,通过试验测试确定螺杆膨胀机的最优工况点(进气压力1.7MPa、膨胀比8、等熵效率0.65),进而设定有机朗肯循环系统的最优运行参数。研究结果表明:加装有机朗肯循环系统后,与原柴油机相比,车用柴油机-有机朗肯循环联合系统的输出功率最大提升了30.6kW,热效率最大提升了10.99%,余热回收效率最高可达10.61%,有效燃油消耗率最大降低了35g/(kW·h)。     

4-kW有机朗肯循环系统运行特性实验研究

针对分布式发电系统的多工况运行需求,测试了采用R123工质的4.0 kW级有机朗肯循环实验机组在150℃热源条件下,基于工质流量和膨胀机转速控制的多工况运行特性和输出性能。结果表明：机组在膨胀机转速1 000～1 200 r/min性能最佳,提高工质流量可明显改善机组性能;膨胀机输出功和净功效率随工质流量变化趋势相反,在大流量下获得最大输出功3.7 kW,在小流量下取得最大热效率6.41%。涡旋膨胀机内容积比相对较小,机组在测试工况下均运行于欠膨胀状态,其等熵效率在50.0%～60.0%,随工质流量和膨胀机转速的增大而增大。     

内燃机余热驱动的储热式有机朗肯循环试验研究

为了提高尾气余热利用率并削弱热源波动对有机朗肯循环的影响,提出了一种集成相变储热换热器的有机朗肯循环（organic Rankine cycle,ORC）系统,利用相变材料削弱尾气余热波动并储存热量。搭建了内燃机尾气余热直接驱动的储热式有机朗肯循环试验台架,开展了内燃机稳态工况和阶跃变工况下储热式有机朗肯循环的热力学性能和动态性能试验研究。结果表明,内燃机稳态工况下尾气平均温度和平均流量为342℃和0.142kg/s,蒸发压力为0.75MPa条件下储热式ORC系统平均输出功率约3.43kW,平均热效率可达到12.7%,平均尾气余热回收率可达40.1%。内燃机阶跃工况下,工质出口温度、蒸发压力和过热度均呈现快速下降的趋势。试验结果还表明储热式ORC具备完全抵御发动机工况小幅波动的能力。在发动机工况阶跃变化比例过大时,储热换热器可以实现对尾气的补热,从而延长储热式ORC的安全工作时间。     

基于ORC的柴油机排气余热回收蒸发器传热特性试验与数值分析

针对某款柴油机排气余热能量,试制一种板翅式蒸发器并建立热力学模型,通过柴油机排气余热台架试验数据验证模型的准确性与有效性,分析有机朗肯循环(ORC)R245fa工质流量与柴油机排气流量的匹配关系及对蒸发器传热特性和ORC性能的影响。结果表明:在各转速满载工况下,工质流量可在有效工作区间内连续变化,而不必局限于某一指定流量,在该区间内蒸发器及ORC输出净功率和热效率均能保持较好的热力性能;蒸发器传热能力主要受工质影响,在低转速小流量时,蒸发器效能和传热单元数较高,但蒸发器传热系数和传热面积的乘积(UA)和回收的排气能量较低,限制了ORC在低转速一般工况下的应用,在高转速大流量时,传热单元数较低,但UA值和排气余热能量较高,可回收较多的排气余热能量。     

有机朗肯循环系统损实验研究

可再生能源及余热发电是低品位能源一种高效利用模式,有机朗肯循环发电系统比水蒸气发电机组更适用于低温热源发电。设计并搭建了热源功率为100kW的导热油模拟热源的有机朗肯循环发电系统,研究冷热源参数恒定不变、膨胀机转速变化时发电系统主要设备的损失和所占比例。主要结论为:当膨胀机转速增加时,蒸发器、膨胀机和工质泵的损失增大,而冷凝器设备损失减少;定量分析膨胀机转速为3000r/min时,蒸发器损失为51.8%,占有机朗肯循环系统损失的1/2以上,工质泵损失最小,仅为1.8%。     

柴油机工况对中温有机朗肯循环性能影响的模拟

根据某重型车用柴油机的试验数据,选用两种不同的排气状态作为设计点,分别设计了两套中温有机朗肯循环余热回收系统.通过理论计算,对比了两套系统的工质蒸发率、各节点温度、系统效率及输出功率等参数随排气温度变化的规律,并主要针对第2套设计方案系统研究了排气流量、排气温度等参数对中温朗肯循环系统效率的影响.结果表明:选择中高工况...     

基于proⅡ的回热/无回热朗肯循环的流程模拟

文中介绍了有回热/无回热有机朗肯循环,并对其进行了理论分析和基于pro II软件对朗肯循环的流程模拟。并针对某化工厂80℃左右的热水,以丁烷为工质,探讨了蒸发器冷源的工质的状态为饱和态和过热态对有回热/无回热朗肯循环的膨胀机输出功和朗肯循环的循环热效率的影响。当工质的状态为饱和状态时,对有无回热的朗肯循环影响不大。但是,当工质的状态为过热态时,有回热的朗肯循环的膨胀机输出功和热循环效率比无回热的朗肯循环要大。这说明增加回热器是很有必要的,它可使能量的回收利用大大增加。     

基于变窄点温差法的有机朗肯循环工质热物性与循环性能的研究

对基于有机朗肯循环的车用汽油机余热能回收利用系统进行了研究。根据试验所采用的蒸发器在MATLAB中建立了循环系统模型,采用变窄点温差的方法,计算分析了28种工质在不同蒸发压力下热物性与循环性能的关系。结果表明:工质的窄点温差随工质蒸发压力变化而变化,在蒸发压力从0.5MPa升至2.5MPa过程中,窄点温差变化均接近30℃,需要在变窄点温差的基础上比较工质热物性与循环性能的关系;临界温度越高的工质其循环效率相对越低;在不同的蒸发压力下,均存在蒸发温度与临界温度之比的最优区间,在此区间内的工质循环效率最高,且该区间随压力的升高而右移;在所给定的入口条件下,湿工质的循环功率最高,等熵工质其次,干工质输出功率最小。     

梯形循环及模拟有机朗肯循环的理论研究

基于有机朗肯循环,提出梯形循环及其理论模型,分析梯形循环与有机朗肯循环之间的偏差。分析表明:当蒸发温度低于临界温度5℃时,梯形循环与有机朗肯循环的偏差小于5%;优化工况下的蒸发温度、最大净输出功及其热效率的相对偏差分别小于2.62%、2.42%、6.21%。基于前期研究提出的优化工况下蒸发温度、最大净输出功和热效率的经验公式进行偏差与应用范围的分析,得到经验公式与有机朗肯循环(及梯形循环)之间的相对偏差分别为优化蒸发温度小于3.26%(1.42%)、最大净输出功小于3.14%(2.46%)和热效率小于5.53%(3.06%)。梯形循环与经验公式可不受具体工质与循环构型的限制,开展有机朗肯循环的拓展性研究,研究有机朗肯循环(或梯形循环)的一般性热力学规律。     

Efficiency of hydrogen internal combustion engine combined with open steam Rankine cycle recovering water and waste heat

A hydrogen internal combustion engine (HICE) wastes more heat, and producing nearly three times more water than a conventional engine. This paper describes the principle behind a novel waste heat recovery sub-system that exploits the water produced by an HICE as the working fluid for an open-cycle power generation system based on the Rankine cycle. Water from the HICE exhaust is superheated by the waste heat from the HICE and used to produce power in a steam expander. A fundamental thermodynamic model shows the contribution of the sub-system to the overall thermal efficiency of the HICE at various engine speeds, with and without a condenser. The results show that the condenser is not cost-effective and that the overall thermal efficiency with the proposed sub-system is 27.2% to 33.6%, representing improvements of 2.9% to 3.7%, at engine speeds of 1500 to 4500 rpm.     

Heat exchanger network design of an organic Rankine cycle integrated waste heat recovery system of a marine vessel using pinch point analysis

The coexistence of different kinds of waste heat sources on marine vessels with various temperature ranges increases the need for an optimal heat exchanger network (HEN) design for the heat collection process to reduce the unutilizable heat that needs to be discharged to overboard. The optimal HEN design has not been taken into consideration by using pinch point analysis in previous studies of marine organic Rankine cycle (ORC) systems that utilize from different kinds of waste heat sources. The objective of the study is to determine the optimal HEN design for an ORC integrated waste heat recovery system of a marine vessel by utilizing the pinch point analysis to improve the overall energy efficiency. Lubricating oil, high-temperature cooling water and scavenge air of the main engine, and the exhaust gas emitted from the boiler plant were identified as the major waste heat sources of a reference container ship. A heat collection stream, in which thermal oil is used as the heat transfer fluid that transfers the collected heat to an ORC system, was proposed. The pinch point analysis showed that the optimum waste heat recovery could be gained by separating the scavenge air cooler into three stages and the lubricating oil cooler into two stages. The results of the parametric study for the varying evaporator inlet pressure between 1000 and 3000 kPa showed that R1234ze(Z) yields the best performance among nine different organic working fluids with the thermal efficiency and exergy efficiency of 15.24% and 86.47% for the ORC system, respectively. For the proposed configuration, the unavailable waste heat that cannot be transferred to thermal oil was found as 23.71%, 16.56%, 13.17%, and 7.81% of the total waste heat produced by the heat sources, and also 8.24%, 9.80%, 11.55%, and 12.93% of the net power output produced by the main engine can be recovered for 25%, 50%, 76%, and 100% maximum continuous rating (MCR), respectively.     

Experimental investigation of a scroll expander for an organic Rankine cycle

This paper presents experimental investigation of the performance of an organic Rankine cycle (ORC) with scroll expander which utilizes renewable, process and waste heats. An ORC test bench is built with a scroll expander‐generator unit modified from a refrigeration compressor‐electrical drive unit. A detailed experimental investigation within the test bench is performed with the organic working fluid R134a. The results show that scroll expander can effectively be used in low‐power ORC to generate mechanical work or electricity from low‐temperature thermal sources (e.g. 80–200 °C, respectively). The experiments are performed under fixed intake conditions into the expander. The pressure ratio and the load connected to the expander‐generator unit were varied. It is found that an optimum pressure ratio and an optimum angular speed co‐exist. When operating optimally, the expander's isentropic efficiency is the highest. The optimum angular speed is around 171 rad/s which corresponds to a generated voltage of 18.6 V. The optimum pressure ratio is about 4. The isentropic efficiency at optimum operation is found in the range of 0.5 to 0.64, depending on the intake conditions. The volumetric efficiency overpasses 0.9 at optimum operation and degrades significantly if the load is increased over the optimum load. A regenerative ORC equipped with the studied expender‐generator unit that operates under 120 °C heat source and has an air cooled condenser generates 920 W net power with efficiencies of 8.5% energetically and 35% exergetically. Copyright © 2014 John Wiley & Sons, Ltd.     

Thermodynamic optimization of Stirling heat engine with methane gas using finite speed thermodynamic model

With the daily rise in environmental issues due to the use of conventional fuels, researchers are motivated to use renewable energy sources. One of such waste heat and low-temperature differential driven energy sources is the Stirling engine. The performance of the Stirling engine can be improved by finding out the optimum operating and geometrical parameters with suitable working gas and thermal model. Based on this motivation, the current work focuses on the multiobjective optimization of the Stirling engine using the finite speed thermodynamic model and methane gas as the working fluid. Considering output power and pressure drop as two objective functions, the system is optimized using 11 geometrical and thermal design parameters. The optimization results are obtained in the form of the Pareto frontier. A sensitivity assessment is carried out to observe the decision variables, which are having a more sensitive effect on the optimization objectives. Optimization results reveal that 99.83% change in power output and 78% change in total pressure drop can take place in the two-dimensional optimization space. The optimal solution closest to the ideal solution has output power and pressure drop values as 12.31 kW and 22.76 kPa, respectively.     

废气涡轮增压汽油机进气系统的优化研究

对废气涡轮增压汽油机的进气管和配气相位进行优化研究.进气管优化采用模糊数学优化方法,优化后汽油机在中速区时性能参数改善较好,其中充气效率和扭矩最大增加量分别为1.4％、1.9％;配气相位优化以GT - POWER软件为研究工具,获得了不同转速工况下的最佳值,优化后汽油机的充气效率和扭矩在低、高速区域增加较大,其中充气效率和转矩的最大增加量为13.4％、19.8％.经过分析优化进气系统后,废气涡轮增压汽油机性能得到了提高.     

Cascaded waste‐heat recovery as a green technology for energy sustainability in power generation

In this work, the Cascaded waste‐heat recovery (WHR) is analyzed from the thermodynamic point of view. Typically, WHR is most effective with small gas turbines and old machines which have a relatively higher design mass flow per kW and higher exhaust temperatures than new designs. The working fluid used in the WHR technology is propane, which vaporizes and condenses at low temperatures. The temperature of the heat source, the outlet pressure of the two expanders, and the mass flow rate of the working fluid are assumed as working variables of the technology. The effect of these variables on the thermal efficiency and power output is evaluated. The obtained results are analyzed and discussed. The results of the calculation are also compared with similar published studies. The overall efficiency considering the gas turbine upstream ranges from about 35% up to 39%. The highest efficiency and power output of the WHR alone at 900 K heat source temperature, 800 kPa condenser pressure, and 100 kg/s mass‐flow rate are 30% and 18 MW, respectively, for two‐expander WHR, and 18% and 9 MW, respectively, for single expander WHR. Copyright © 2014 John Wiley & Sons, Ltd.     

低温余热发电系统中涡轮膨胀机的优化研究

以R152a为循环工质,对低温余热发电系统中径流涡轮式膨胀机进行了研究;采用EES(Engineering Equation Solver)软件编程对涡轮膨胀机进行了热力设计,其轮周效率、内效率分别可达90.19%和88.84%,输出功率为50 kW;对所设计的膨胀机进行性能分析发现:随着膨胀机入口工质温度的升高,其内效率稍有下降,而输出功率大幅增加;对应膨胀机大功率条件下的是较高的比转速Ns和较小的比直径Ds,符合未来高性能涡轮式膨胀机"大功率,高转速,小尺寸"的发展趋势。     

Analysis of exhaust waste heat recovery from a dual fuel low temperature combustion engine using an Organic Rankine Cycle

This paper examines the exhaust waste heat recovery potential of a high-efficiency, low-emissions dual fuel low temperature combustion engine using an Organic Rankine Cycle (ORC). Potential improvements in fuel conversion efficiency (FCE) and specific emissions (NO_x and CO₂) with hot exhaust gas recirculation (EGR) and ORC turbocompounding were quantified over a range of injection timings and engine loads. With hot EGR and ORC turbocompounding, FCE improved by an average of 7 percentage points for all injection timings and loads while NO_x and CO₂ emissions recorded an 18 percent (average) decrease. From pinch-point analysis of the ORC evaporator, ORC heat exchanger effectiveness (?), percent EGR, and exhaust manifold pressure were identified as important design parameters. Higher pinch point temperature differences (PPTD) uniformly yielded greater exergy destruction in the ORC evaporator, irrespective of engine operating conditions. Increasing percent EGR yielded higher FCEs and stable engine operation but also increased exergy destruction in the ORC evaporator. It was observed that hot EGR can prevent water condensation in the ORC evaporator, thereby reducing corrosion potential in the exhaust piping. Higher ? values yielded lower PPTD and higher exergy efficiencies while lower ? values decreased post-evaporator exhaust temperatures below water condensation temperatures and reduced exergy efficiencies.     

海上油气平台余热朗肯循环发电系统热力学分析

海上油气平台存在大量的燃气轮机余热。通过建立海上平台余热朗肯循环发电系统仿真模型,开展平台余热发电热力学及热经济性分析。选取工质泵功率、发电机输出功率、系统热效率、换热面积和单位面积发电量等参数作为优化目标,研究不同冷凝温度下优化目标函数随蒸发器烟气进出口温差的变化规律。结果表明:随着蒸发器烟气进出口温差的增加,工质泵功率、发电机输出功率和系统APR先增大后减小。冷凝温度越高,工质泵功率越大,发电机输出功率和系统热效率越小。当冷凝温度为65℃时,系统APR最大。受透平出口蒸汽干度的限制,所研究工况下,系统发电机最大输出功率为7 496 kW,系统最大热效率和APR分别为14.16%和5 kW·m~(-2)。研究结果可为撬装化、集成化海上油气平台余热发电系统研制提供理论参考。     

内燃机尾气余热驱动有机朗肯蒸汽压缩制冷循环的研究

设计了以内燃机尾气余热为热源驱动的有机朗肯蒸气压缩制冷循环系统。根据热力学定律,建立了循环系统的数学模型,提出了尾气换热夹点确定方法。以Matlab和Refprop软件为工具,研究了有机朗肯循环(organic Rankine cycle,ORC)各换热器负荷、做功量、热效率分别随蒸发压力、冷凝温度的变化关系,并确定了最优工质。研究了蒸汽压缩制冷循环(vapor compression refrigeration,VCR)各换热器负荷、制冷系数分别随蒸发温度、冷凝温度的变化关系。由于压缩比的限制,确定了多种制冷工质在不同冷凝温度下的最低蒸发温度,结合相关标准中所规定的各型冷藏车蒸发温度的范围,确定了各型冷藏车的可选制冷剂。研究了与可选工质对应的制冷系数随蒸发温度的变化关系,从而确定最优工质。计算了各型冷藏车在采用最优制冷剂时,在最严苛工况下的制冷量、制冷系数及综合系数。