对使用混合燃料的低温有机朗肯循环发动机排气余热的回收分析.docx

1、对使用混合燃料的低温有机朗肯循环发动机排气余热的回收分析外文翻译题目:对使用混合燃料的低温有机朗肯循环发动机排气余热的回收分析学院(系)： 机械工程学院 专 业： 热能与动力工程 班 级： 2011级1班 学 号： 1101210414 学生姓名： 卢一乐 指导老师： 李会芬 副教授 二一五年三月十三日对使用混合燃料的低温有机朗肯循环发动机排气余热的回收分析摘 要本篇论文说明有机朗肯循环(ORC)的混合燃料低温发动机的排气余热利用具有高效节能、低排放的特点。燃料转换率、特定排放物（NOx和CO2）、排气再循环和有机朗肯循环涡轮复合，这几项的改善的潜力可量化为喷油正时的范围和引擎负荷大小。伴随高

2、温EGR和ORC涡轮复合，当NOx和CO2的排放减少18%，FCE对全部的喷油正时和负荷来说，平均提高了7%。有机朗肯循环蒸发器、有机朗肯循环热交换器效率、EGR率和排气歧管压力的节点分析被认为是重要的设计参数。更高的节点温差在有机朗肯循环蒸发器中均匀产生了更大的减。忽略发动机的运行条件。 增加的EGR率产生了更高的FCE率和稳定的内燃机工况，但是也在ORC蒸发器的减也更多。值的增加导致PPTD变低和更高的率。 当值变低，快速蒸发器废气温度低于水的冷凝温度并且导致效率降低。据观察，高温废气再循环可以阻止水在ORC蒸发器中冷凝，从而减少对排气管道潜在的腐蚀。关键词：废热利用 有机朗肯循环 双燃料

3、发动机 低温燃烧1.介绍国家能源安全，能源价格上升，全球市场竞争加剧，加上严格的保护环境排放法规，这几点是寻找可持续发展并且经济低廉的技术去提高效率和寻找更清洁的方法来实现能量转化和利用的主要发展驱动力，即：。内燃机(IC)是追求大功率和高效的最主要机器。由于燃料相对便宜又实用，十年来，内燃机已经在大功率和低排放方面充分发展。然而，近年来随着能源价格上升和对能源可持续性的担忧，内燃机的效率提高变得日益重要。在过去的150年里，内燃机在提高燃料转换和降低排放方面取得了巨大的进步。事实证明，路上的平均峰值制动的热效率 ，火花点火传动试验大约是30%，压缩点火试验能达到约41% 1。深入提高燃料转化

4、率需要系统化、标准化分析各种各样的内燃机损耗。可以通过建立内燃机热力学模型来进行分析。这就要求热力学第二定律基于多过程燃料化学减少不可逆的模型。热力学第一定律基于热力学模型使得更加容易精确计算能量，也就是说，它们在计算燃烧过程的热损失时非常有用。但是这些模型并不能计算出实际上利用了多少浪费的能量来做有用功或.1.1燃烧过程中 选择性看待减在内燃机的燃烧过程中中的减实验已经被许多研究人员积极研究分析，可能发现一些先前不被注意的地方。利奥尔和鲁迪2用热力学第二定律分析了一个理想奥托循环，他们得出的结论是：狭义的热力学第一定律分析并不能证明在燃烧过程中丢失的潜能。的分析显示，这些损失的能力甚至跟传动

5、功相当。他们建议使用底循环去还原排气装置中的减。邓巴和利奥尔3测试了恒压隔热下氢气和甲烷燃烧的减，他们得出了在绝热燃烧中，最主要的减途径就是内部热能的交换。他们认为内部热能交换存在于内部高温产物和相对低温的未反应物之间的热传导。温差使得内部产生了热传递，因此，也产生了减。卡顿4在利用热力学第二定律去研究内燃机的著作里提出了一个广义的分析。这类型的著作认为，现象型燃烧模型基本上由模型的气体交换和燃烧过程中的质量、能量和平衡方程组成。从这些分析结果里面可以知道：1、可利用能量或者用来做有用功的能量随着燃烧温度的提高而增加。2、经过不可逆的燃烧过程减少，热传导通过有限的温差和排气过程实现。大多数研究

6、得出了由于不可逆燃烧，大约20%-30%燃料的化学会减少的结论。3、燃烧时空气过量或者稀薄燃烧都会比理论燃烧和富氧燃烧有更有效的减。4、利用排气余热去产生额外有用功去补充输出功率具有巨大的潜力。很明显，有2种更好使用燃料化学的方法。第一种主要是在燃烧过程中将减最小化。第二种是通过利用排气来提升更大的原动力热效率。废热利用时使用朗肯底循环涉及到了使用内燃机加热相应液体排出的高温废气的显焓，而饱和或者过热的蒸汽更好，然后蒸汽显焓被用于涡轮做有用功。这篇论文讲述了使用有机朗肯循环（即ORC）来实现废热利用。2.提前低压导阀点燃天然气（ALPING）燃烧在保证低排放物的同时提高发动机燃料效率仍然是内燃

7、机设计者的主要难题。为了解决问题，工程师们正在试验先进的燃烧领域例如低温燃烧（LTC）32。LTC与传统的柴油燃烧相比，当柴油燃料效率相同时，LTC在降低排放方面有很大的优势，尤其是氮氧化物(NOx )和颗粒物(PM)。然而，许多LTC方法有个很难克服的缺陷。尽管它们的NOx 和 PM排放更少，LTC却排放了大得多的碳化氢(HC) 和一氧化碳(CO)。更重要的是，在高负荷时失去对燃烧的控制否决了大部分通过实现内燃机制动的LTC方法，也就是说，有效压力(BMEP)（或者负荷）会增大5-6巴。所以，必须要有更先进的方法去改善发动机的工况和降低LTC的排放物(HC & CO)。ALPING LTC学

8、派的学者在最近的实验结果中显示33,34：得到了很好的燃料转换效率（40%）并且NOx排放率很低(0.25 g/kWh)。在ALPING燃烧中，早于压缩冲程就由很小的阀射出柴油喷雾，(60 在上止点之前 BTDC)去点燃预先混合的稀薄混合气体，并且实现了局部预混和控制LTC。从能量的角度来看，这个小小的燃料（柴油）阀贡献了2%-5%的燃料总化学能，同时保留了天然气提供的95%-98%的能量。ALPING LTC的提前喷射阀使得点火延迟，从而有了足够的时间给喷出的柴油与天然气、吸进的空气充分混合。在随后的压缩过程中，如果当地温度和压强有利于点燃，柴油自动点燃，随后开始天然气的部分预混燃烧。ALP

9、ING LTC的部分预混导致相对降低了当地温度，也显著减少了NOx的生成率。进一步地说，凭借本地的条件意味着PM排放可能是可以忽略的。她的LTC理念与HCCI35这类比较起来，ALPING LTC利用LTC在相对高输出功率带来的优势去负责控制发动机工况。实验证明，在单缸发动机上，在高达12巴的有效压力时，可实现ALPING LTC的效率和减排。8.结论在本篇论文中，先进方法对排气余热利用的潜力巨大，低温、低排放、高效率在提前低压导阀点燃天然气（ALPING）、使用底有机朗肯循环（ORC）的低温燃烧(LTC)中得以验证。燃料转换率（FCE）和排放物（NOx和CO2）明显下降的潜力被高温EGR和使

10、用有机朗肯循环涡轮复合的排气余热利用（WHR）挖掘出来。此外，有机朗肯循环的底循环不可逆性是依据热力学第二定律得出， 有机朗肯循环的蒸发器的基本设计标准是建立在使用“节点”的分析上的。分析可以得出以下结论：1.伴随高温EGR的条件，所有的喷油正时在一半和四分之一负荷时可以提高FCE，有机朗肯循环涡轮复合随着高温EGR甚至更高效。例如，在60上止点之前的喷射正时和四分之一负荷 ，FCE从价值 20%-28%的基线（0%EGR）仅仅伴随着22%的EGR上升，并且，逐渐达到32%都伴随着22%EGR和ORC涡轮复合。半负荷FCE提高在60上止点之前喷射正时是更加理想的（从30%在0%EGR开始，达到

11、40%在8%EGR和ORC涡轮复合），因此ORC涡轮复合的废气余热利用在四分之一负荷时更合理。2.发动机排出的特定排放物NOx和CO2可以通过ORC涡轮复合大幅减少，并且不用降低FCE，不用改变燃烧过程也无须昂贵的排放处理设备。有了ORC涡轮复合，NOx和CO2的排放都减少了大约18%（平均水平下）。3.对于所有的喷油正时，ORC蒸发器里的废气和有机流体（R113）的饱和温度之间节点温差（PPTD）随着EGR的增长而上升，这表示热传导潜力更大。然而，忽略发动机负荷、喷油正时或者EGR率，更高的节点温度值都会导致ORC蒸发器的率降低，即更大的减。4.随着高温EGR的提升，在ORC蒸发器里的减更大

12、。然而，EGR促进更稳定的发动机工况、更高的FCE和更低的排放。进一步来说，高温EGR的增加确保了，快速蒸发器废气温度高于“冷凝线”，也就是说，高温EGR将阻止ORC蒸发器管中水的冷却从而减少对排气歧管的腐蚀。5 .ORC蒸发器的热交换器效率()被认为是一个重要的设计参数。一般来说，增加的值(=0.8)使得PPTD更低和率更高；降低的值(=0.6)会使快速蒸发器的废气温度低于到水的冷凝温度（给定歧管压力）并且减少了率。然而，依靠提高值将增大热交换损失。因此，ORC热交换器效率、排气歧管压力、EGR率这3个参数必须缜密决定才能确保在ORC率、机器成本、机器效率、废气排放和整体燃料转换率之间达到最

13、好的平衡。Analysis of exhaust waste heat recovery from a dual fuel low temperature combustion engine using an Organic Rankine CycleAbstractThis paper examines the exhaust waste heat recovery potential of a high-efficiency, low-emissions dual fuel low temperature combustion engine using an Organic Rankine

14、 Cycle (ORC). Potential improvements in fuel conversion efficiency (FCE) and specific emissions (NOx 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

15、an average of 7 percentage points for all injection timings and loads while NOx 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 de

16、sign 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 ev

17、aporator. 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 conde

18、nsation temperatures and reduced exergy efficiencies.Keywords:Waste heat recovery；Organic Rankine Cycle；Dual fuel engines；Low temperature combustion1. IntroductionNational energy security, rising energy prices, increasingly competitive global markets, and stringent environmental emissions regulation

19、s are primary driving forces in the search for sustainable and economically viable technologies for efficient and clean approaches to energy conversion and utilization. Internal combustion engines (IC) are prime movers of choice when high power densities and efficiencies are desirable. Due to relati

20、vely cheap fuel availability in past decades, IC engines had been optimized for high power densities and low-emissions. However, in recent years, with escalating fuel prices and sustainability concerns, engine efficiency has assumed greater importance.Over the past 150 years since the invention of t

21、he IC engine great strides have been made in improving its fuel conversion efficiency and reducing its emissions. As a testament to this fact, the average peak brake thermal efficiency of on-road spark ignition power trains is about 30% while that of on-road compression ignition power trains is abou

22、t 41% 1. Further improvements in fuel conversion efficiency require a system-level analysis of the various losses encountered in the IC engine. This analysis can begin with thermodynamic modeling of the IC engine. Traditional first law-based thermodynamic models facilitate accurate energy accounting

23、, i.e., they are useful in estimating the net losses associated with the combustion process. But these models do not provide estimates of how much of the wasted energy is actually recoverable as useful work or exergy. This requires second law-based models that track the irreversibilities associated

24、with various processes that destroy fuel chemical exergy.1.1. Selective review of exergy destruction in combustion processesExamination of exergy destruction in internal combustion engine processes has been actively studied by many researchers to identify, and possibly recover some of the lost avail

25、able work. Lior and Rudy 2 performed a second law analysis of an ideal Otto cycle and they concluded that a simple first law analysis does not reveal the magnitude of work-potential lost in the combustion process.The exergy analysis results showed that the magnitude of these losses were comparable t

26、o that of useful shaft work. They recommended the employment of bottoming cycles to recover the exergy destroyed in the exhaust. Dunbar and Lior 3 examine the exergy destruction in constant pressure adiabatic combustion of hydrogen and methane. They conclude that the most important mechanism for exe

27、rgy destruction in adiabatic combustion is internal thermal energy exchange. They defined internal thermal energy exchange as the internal heat transfer between products that are at a high temperature and still unreacted reactants, which are at a lower temperature. This temperature difference provid

28、es a finite temperature gradient for internal heat transfer, and hence, exergy destruction. Caton 4 presents a comprehensive review of literature that utilized second law of thermodynamics to study IC engines. All of the literature reviewed used phenomenological combustion models that basically cons

29、isted of mass, energy and exergy balance equations to model the gas-exchange and combustion processes. Some significant conclusions from this review are:1. The available energy or the energy that can be used to obtain useful work increases with increasing combustion temperature.2. Exergy is destroye

30、d through irreversibilities in the combustion process, heat transfer across a finite temperature difference, and exhaust processes. Most of the studies examined conclude that about 20-30% of fuel chemical exergy is destroyed due to irreversible combustion.3. Combustion in the presence of excess air

31、or lean combustion resulted in greater availability destruction than stoichiometric and rich combustion.4. Potential for utilizing exhaust waste heat to produce additional useful power to complement shaft power.Clearly, there emerge two pathways for better utilization of the chemical exergy of the f

32、uel. The first focuses on minimizing exergy destruction in the combustion process. The second pathway is to tap the exhaust exergy to obtain further improvements in thermal efficiency of the prime mover. Waste heat recovery (WHR) using Rankine bottoming cycles involves the utilization of the sensible enthalpy of the hot exhaust from the IC engine to heat a suitable fluid, preferably to saturated/superheated vapor, and then the sensible enthalpy of the vapor is used to obtain useful work from a turbine.