【作者】 陈征；

【导师】 赵华；

【作者基本信息】 天津大学 ， 动力机械及工程， 2007， 博士

【摘要】 内燃机高效清洁燃烧技术一直是国际内燃机界研究的热点课题。针对未来超低排放、甚至零排放的排放法规,人们提出了不同的内燃机新型燃烧方式。同时,开发新型清洁代用燃料也成为当前各国研究的热点。本文对甲醇代用燃料新型高效清洁燃烧方式进行了探索性研究,即部分甲醇合成二甲醚,实现二甲醚与甲醇双燃料方式,创新性地提出了采用甲醇/DME气道喷射双燃料均质压燃(HCCI)燃烧方式和DME气道喷射与甲醇缸内直喷双燃料复合燃烧方式,以在全负荷范围内实现甲醇的高效清洁燃烧。采用甲醇/DME气道喷射双燃料HCCI燃烧方式,能拓宽发动机运行工况范围到原非增压柴油机中高负荷水平,并能保持极低的NOX排放,但低负荷燃烧效率和热效率低,HC和CO排放高;中高负荷甲醇/DME浓度可调范围窄,控制难度增大。采用EGR后中高负荷工况的可控范围得以拓宽,但其最大负荷范围难以扩展。在低负荷工况,采用纯DME加大比例EGR的HCCI燃烧方案能改善热效率;在中高负荷工况,采用高EGR率高DME比例方案可以提高热效率,降低HC和CO排放。采用DME气道喷射和甲醇缸内直喷双燃料复合燃烧方式,通过控制甲醇的喷射时刻可以实现不同燃烧模式,不同燃烧模式表现出不同的燃烧特性和排放特性。低甲醇浓度下采用高温扩散燃烧模式可以实现低负荷较高的热效率。随甲醇浓度增大,高温扩散燃烧模式出现的时刻提前,早喷燃烧可控范围变窄。采用晚喷方式,燃烧过程能得到较好的控制,高甲醇浓度大负荷下不容易出现爆震燃烧,能进一步扩展发动机负荷工况范围。CFD模拟表明,晚喷在燃烧室壁面附近有较强烈的浓度分层,高温燃烧区范围较窄,主要分布在压缩余隙和燃烧室壁面附近。变参数模拟研究表明,增大喷油速率可以缩短高甲醇浓度晚喷的燃烧持续期。在不同燃烧方式研究的基础上,本文提出了全负荷范围甲醇高效清洁燃烧的控制策略。即在低负荷工况,采用纯DME加大比例EGR的HCCI燃烧或二甲醚气道喷射与甲醇缸内直喷双燃料复合燃烧的甲醇高温扩散燃烧模式以获得相对高的热效率;在中高负荷工况,采用甲醇/二甲醚气道喷射双燃料HCCI燃烧方式实现高效低NOX排放的清洁燃烧;在大负荷工况,采用甲醇晚喷实现DME气道喷射与甲醇缸内直喷复合燃烧方式以保证高的功率输出。这一控制策略为甲醇燃料在内燃机上实现高效清洁利用提供了理论基础和试验依据,具有一定的参考价值。更多还原

【Abstract】 High efficiency and clean combustion technology of internal-combustion engine has been a hotspot in international engine field all along. New engine combustion modes are presented aiming at future ultra-low and even zero emission regulation. At the same time, the development of new clean alternative fuel has also becomes a hotspot of research in many countries. In this paper, new high-efficiency and clean combustion modes of alternative fuel methanol are exploringly investigated. Based on DME and methanol dual-fuel method achieved by DME generation from a part of methanol, two kinds of combustion types are innovatively presented to achieve high efficiency and clean combustion of methanol in full load. One is HCCI combustion of methanol/DME dual-fuel port injection; another is the dual-fuel compound combustion with port injection of DME and direct injection of methanol.HCCI combustion of methanol/DME dual-fuel port injection can extend the operating range to middle-high load level of original non-pressurized diesel engine, keeping very low NOX emissions, but having low combustion efficiency and thermal efficiency, high HC and CO emissions at low load. In addition, adjustable region of methanol/DME concentration at middle-high load is narrow so that combustion control difficulty increases. EGR can enlarge the controlled region at middle-high load, but can’t extend maximum load range. At low load, adopting pure DME HCCI combustion with high EGR rate can improve thermal efficiency. In middle-high load, adopting large DME percentage and high EGR rate can improve thermal efficiency of HCCI and decrease HC and CO emissions.To the dual-fuel compound combustion with port injection of DME and direct injection of methanol, various combustion modes, which represent different combustion characteristics and emissions characteristics, can be achieved by controlling different injection timings of methanol. High temperature diffusion combustion mode should be adopted to attain relatively high thermal efficiency under low methanol concentration and low load. With the increase of methanol concentration, the crank angle corresponding to high temperature diffusion combustion mode advances, and combustion controlled region of early injection becomes narrower. By adopting late injection, combustion process can be well controlled, knocking combustion can be avoided under high methanol concentration and large load, and so engine load range can be further extended. CFD simulation shows that, for late injection case, there is intensive concentration stratified near combustion chamber wall. And high temperature combustion region, which is relatively narrow, is distributed in compression clearance and near combustion chamber wall. Modeling study of varied parameters indicates that faster injection rate can shorten combustion duration under high methanol concentration for late injection.Based on the above study, this paper presents a control strategy for high efficiency and clean combustion of engine fueled with methanol in full load. At low load, pure DME HCCI combustion with high EGR rate or high temperature diffusion combustion mode of methanol should be adopted to attain relatively high thermal efficiency. In middle-high load, HCCI combustion of methanol / DME dual-fuel port injection should be adopted to achieve clean combustion with high efficiency and low NOX emissions. At high load, the dual-fuel compound combustion with port injection of DME and in-cylinder direct injection of methanol achieved by late injection should be adopted to ensure high power output. This control strategy, which provides theoretical and experimental basis for high-efficiency and clean utilization of methanol in engine, has a useful reference value.更多还原