【作者】 闫峰；

【导师】 苏万华；

【作者基本信息】 天津大学 ， 动力机械及工程， 2016， 博士

【摘要】 提高内燃机效率不仅可以有效减少石油供应紧张的压力,还可以缓解由于CO₂排放带来的环境压力。因此,在世界范围内,如何进一步提高内燃机效率已成为内燃机技术最具挑战的课题,受到广泛关注。但是,目前内燃机最高有效热效率仅略大于40%,而内燃机不经“根本性”改造,最大有效热效率很难超过60%。制约活塞式内燃机效率的一个重要原因是其“非约束燃烧”过程损失的做功潜力,这个损失比例高达燃料初始做功潜力的20²5%。因此,理解该损失过程并探索降低损失、最大化‘火用’利用率的方法是今后进一步提高内燃机热效率的新方向。本文结合实验和化学动力学数值模拟,详细研究了内燃机“非约束燃烧”的‘火用’损失过程,探索了最小化内燃机‘火用’损失、最大化‘火用’/功转化效率的新途径。为更好地描述内燃机燃烧过程的‘火用’损失机理,本文创新性地发展了一种计算非平衡态燃烧过程的化学动力学‘火用’损失模型,基于化学动力学和非平衡态热力学中的局部热力学平衡原理,首次明确了复杂化学动力学中每一步基元反应的‘火用’损失,为进一步确定内燃机非平衡态化学反应中最主要的‘火用’损失源、探索减少‘火用’损失的控制方法提供了理论依据。研究并筛选了以正庚烷为例的基础燃料详细的化学动力学模型,确定了其燃烧过程的化学动力学‘火用’损失机理,结合‘火用’损失源和化学动力学特点,归纳总结出了基础燃料燃烧过程的损失特征,并进一步研究了燃烧过程‘火用’损失源的影响因素,探索了高效燃烧反应的约束条件。基于对‘火用’损失源及控制方法的研究,以减少‘火用’损失、节约能量为目的,探索了进一步降低内燃机燃烧过程‘火用’损失的方法,提出了高温无氧燃料重整理念,并从理论上探讨了高温无氧燃料重整的可行性及其在节约系统‘火用’方面的优势。设计和搭建了满足燃料改性要求的化学动力学流动试验台,通过对比实验和模拟结果,讨论了高温无氧重整理念的正确性以及实验系统的可行性。基于对‘火用’损失源的分析和高温无氧燃料重整的研究,探索了提高内燃机热效率的新途径,提出了一种可行的高效内燃机燃烧原理--重整燃料分子均质压燃燃烧（RM-HCCI）,并分别从（1）初始燃料化学‘火用’;（2）燃烧过程‘火用’损失;（3）滞燃期和燃烧持续期;（4）‘火用’/功转化过程等几个方面讨论了RM-HCCI内燃机燃烧原理所具有的理论优势。更多还原

【Abstract】 For the dominant role internal combustion engines(ICEs)have played in transportation and serious energy and environment crisis we have encountered,technologies that could improve engine efficiency,as well as reduce greenhouse gas emissions,attracting more and more popularity in recent years.The highest peak brake thermal efficiency(BTE)of current passenger vehicle engines is only slightly above 40%,and the maximum BTE for slider-crank engines can hardly exceed 60% without radical changes to present engines structure and combustion strategies.A consensus opinion why the maximum BTE for slider-crank engines is limited under 60% is the irreversible ?unrestrained combustions‘ in ICEs,which occur far from thermodynamic equilibrium states that would loss approximately 20–25% of the fuel‘s working potential.Thus,understanding the mechanism of the inefficiencies and seeking for ways to reduce the irreversibility are significant to realize further improvement of the engine efficiency.Both the essential characteristics of ?unrestrained combustion‘ exergy loss process and control approaches to minimize the combustion irreversibility as well as maximize the work extraction efficiency were investigated by experiment and simulation in this study.To better describe the exergy loss mechanism of the combustion process,which is well known as a non-equilibrium physical and chemical process,a new exergy loss computational code on the basis of the entropy generation equation,aiming to quantify the exergy loss behavior of each individual elementary reaction,is innovatively developed according to the local equilibrium hypothesis of non-equilibrium thermodynamics,which provides a theoretical basis to explore the main intrinsic irreversible sources of the non-equilibrium combustion process.The present study investigated the intrinsic exergy loss sources of a primary reference fuel(n-heptane)by detailed chemical kinetics.Three apparent peaks in the overall exergy loss rate during combustion process,with each peak caused by very different element reactions,were observed based on the microscopic exergy loss events.Then,we detailed the effects of various parameters on exergy loss events within the overall exergy loss rates,exergy loss rates of individual reactions,and loss distributions.A high temperature and no oxygen atmosphere fuel reforming has been proposed for the purpose of exergy saving by theoretical analyzing the detailed exergy loss events of combustion process,the correctness and feasibility of this fuel reforming have been verified through experiments.The exergy behaviors of high temperature and no oxygen atmosphere fuel reforming have been extensively studied,and many benefits had been observed including:(1)simplify the reforming device;(2)improve the total chemical exergy while effectively converting large moleculae to small moleculae;(3)improve the mixture‘s ratio of specific heat capacity for higher work-extraction;and(4)Longer ignition delay for better mixing process.Furthermore,a promising high efficiency RM-HCCI(Reformed molecule HCCI)combustion principle was proposed.In a RM-HCCI engine,large hydrocarbon fuels were reformed into small molecule fuels under high temperature and no oxygen atmosphere before injected into the cylinder when the exhaust gas enthalpy to a certain extent was recovered,further improving the engine efficiency.The RM-HCCI has many advantages:(1)less exergy losses during combustion processes,(2)longer ignition delays and shorter but controlled combustion durations,(3)improved ratio of specific heats,all these advantages show us a bright further of improving engine efficiency by RM-HCCI combustion principle.更多还原