【作者】 王云开；

【导师】 于秀敏；

【作者基本信息】 吉林大学 ， 动力机械及工程， 2011， 博士

【摘要】 可控自燃是一种燃烧方式的革新,从20世纪末就开始受到世界主要汽车公司和内燃机研究机构的注意和研发。其特征是均质混合气压燃和低温燃烧,综合了汽油机和柴油机燃烧的优点,对实现内燃机高效燃烧、降低排放等方面有重要的研究价值。通过无凸轮配气机构来控制残余废气量是实现可控自燃简单有效的途径之一本文自主开发了无凸轮轴电液配气机构,该机构控制灵活,重复性好。实现了气门正时可变,气门升程可变。设计的二级驱动柱塞能同时满足气门开启迅速和减少流量的要求,利用缓冲装置实现了最大升程和落座软冲击,降低了系统工作噪声,提高了系统的工作寿命。建立了电液气门运动数学模型,利用Matlab进行了仿真计算研究,探索了电液气门运动性能的影响因素,该仿真研究在辅助电液气门机构设计、确定和优化系统参数及缩短机构开发周期等方面具有重要意义。建立了无凸轮轴电液配气机构模拟试验平台,利用开发的数据采集系统进行了该配气机构性能实验。试验表明：在液压力和油液温度恒定的状态下,进排气门开启和关闭延迟时间符合正态分布；气门关闭过程与液压力无关,随着温度的升高,气门关闭响应延迟有下降的趋势；在液压力6.5MPa时,进气能力与原机相似,气门的落座瞬间速度为0.08m/s。在液压力11Mpa时,气门落座瞬间速度为0.12m/s,实现了气门柔性着陆；在不改变液压力情况下,气门的开启和关闭升程曲线形状相似,机构具有很好的重复性和可靠性。改变系统液压力就可以实现气门升程从3.1mm-11mm连续变化。建立了电控单缸无凸轮轴汽油发动机样机,开发了无凸轮轴发动机控制单元硬件和软件。采用前馈开环控制策略,通过查找气门正时脉谱图,可以保证无凸轮轴配气机构在转速为2200r/min以下正常工作,气门的开启和关闭正时重复性较好；制备了SI燃烧方式的基本喷油脉宽和基本点火提前角脉谱图,在配气相位相同的情况下,无凸轮轴发动机达到了原凸轮轴发动机的动力性,而且在一些工况下,比原凸轮轴发动机略有提高,在经济性和排放性能上,与原凸轮轴发动机性能基本相同,为进行下一步试验提供了很好的基础条件。在开发的无凸轮轴发动机样机上,首次在国内利用排气门二次开启(SEVO)模式下的缸内EGR实现了CAI燃烧,研究了该模式下CAI燃烧特点、排放情况及工作区域,并进行了SI燃烧到CAI燃烧的转换研究。试验表明：该模式下的CAI燃烧有二次压缩现象,主要是因为在排气门首次关闭时,早于原始配气相位,造成了一定的高温废气留在气缸中,产生了二次压缩,其最高压力为0.5MPa左右,低于采用负气门重叠角实现CAI燃烧时的二次压缩最高压力1.2MPa；CAI燃烧的指示热效率为0.3644,同负荷下的SI燃烧效率为0.3313,提高了10%；在发动机转速为1000r/min,保持排气门第一次开启和关闭正时、进气门关闭正时不变,调整进气门开启正时和排气门二次开启正时,将试验中实现CAI稳定、非敲缸燃烧不同工况点下的进气门和排气二次启闭正时点制成CAI燃烧区域。此区域IVO从18°CA ATDC到60°CA ATDC变化,SEVO从18。CA ATDC到46°CA ATDC变化,过量空气系数为1。在CAI正常燃烧区域左侧区域为EGR率过小失火区域,右侧区域为EGR率过大失火区域,当进气门开启正时(IVO)大于60°CA ATDC寸,基本不能实现CAI正常燃烧,但是可以采用火花助燃的方式实现稳定燃烧。整个CAI燃烧区域的EGR率为40%-57%,BMEP为0.227MPa-0.401MPa,当SEVO正时不变时,独立调节IVO正时,就可以控制发动机的负荷。有效热效率为0.25-0.31,CAI燃烧区域大部分的有效热效率在0.284以上,对应的EGR率区域为39.6%-43%,大部分区域内NOX排放低于140ppm。试验中发现温度对CAI的稳定燃烧有非常大的影响,包括发动机的水温、进气温度、特别是排气温度,当排气道温度低于633K时,CAI处于失火状态。从S1转换到CAI可以在一个循环内完成,两个循环内到达稳定燃烧状态。由于排气温度高使CAI首循环燃烧迅速,燃烧的最高压力出现在0°CA ATDC附近。更多还原

【Abstract】 Controlled auto-ignition (CAI) is an innovative combustion process which has been receiving worldwide attention from major automotive manufacturers and engine research institutions. Characterized by its homogenous charge auto-ignition by compression and low temperature combustion, CAI mode is able to realize high thermal efficiency and low engine-out emissions showing great research potential. Trapping or re-breathing high temperature burnt gas via cam-less valve train proves to be a simple and effective method to obtain CAI combustion.An electro-hydraulic cam-less valve train was developed in this thesis aimed to achieve variable engine valve phase and valve lift. Two-stage hydraulic piston mechanism was featured by fast engine valve opening and low flow ratio requirement. Cushioning system was used to avoid mechanical impact between hydraulic piston and its stop, which reduced the working noise and improved the valve train endurance. A Matlab model of this electro-hydraulic valve train was previously built to assist system design. Items showing effect on the system performance were numerically explored. Thanks to this numerical model, working parameters was finally determined and optimized.Test bench for this cam-less valve train was established and valve train system functionalities were analyzed through the data acquisition system. The results indicated a normal distribution for the intake and exhaust valve opening and closing delay at constant working fluid pressure and temperature. While the valve closure has nothing to do with the working pressure, higher fluid temperature claimed a faster valve closing response. Soft landing was achieved with seating velocity effectively reduced to 0.08 m/s. Valve lift swept from 3.1 mm to 11 mm while changing the working pressure. Obtained valve opening and closing profile showed great repeatability at constant working pressure.Engine test platform was established with cam-less valve train mounted on the engine head and fully controlled with self-developed electrical management system. With open-loop feedforward control strategy by looking up valve phasing map, cam-less valve train ensured engine speed up to 2200 r/min. Basic fuel injection pulse and optimal ignition advanced angle were sampled. After calibration, cam-less engine reached the power of original engine with camshaft, and even higher at some operating points. Fuel economy and emission performances reached the same level with original engine. Stable CAI combustion with second exhaust valve event was firstly achieved on the engine test platform in our country. CAI combustion, emission features and operation region were studied. Mode transition between SI and CAI was also analyzed. In this study, exhaust gas recompression process was observed on the pressure history due to the trapped burnt gas as a result of advanced first exhaust valve closing. Recompression peak pressure was 0.5MPa, lower than that of NVO strategy,1.2MPa. Experiment results revealed that indicated thermal efficiency was 0.3644 at selected operating points,10% higher than that of SI mode.Stable CAI combustion region was obtained as a function of IVO and SEVO, with fixed equivalence F/A ratio of approximately stoichiometric and with fixed exhaust valve event and fixed IVC at engine speed of 1000 r/min. Within this operation region, IVO timing swept from 18°CA ATDC to 60°CA ATDC and SEVO timing swept from 18°CA ATDC to 46°CA ATDC. Left side of this region with early IVO was limited by misfire due to its lower EGR rate; on the other hand, right side of this region was restricted by misfire owing to the extreme lean fresh charge. Even delayed IVO timing implied CAI misfire. EGR rate, adjusted by varying IVO or SEVO timing, ranged from 40% to 57%. Within the entire CAI region, BMEP swept from 0.227MPa to 0.401MPa. With second exhaust valve closing kept constant, engine load could be altered by adjusting the IVO timing. The brake thermal efficiency swept from 0.25 to 0.31, higher than 0.284 in most of this region, with corresponding EGR rate from 39.6% to 43% and NOx emission lower than 140ppm. Experiment tests indicated that temperatures, includes cooling water temperature, intake charge temperature and especially, exhaust gas temperature, had significant influence on the CAI combustion. Misfire occurred for the operating points with exhaust gas temperature lower than 633K.Mode transition from spark ignition (SI) to CAI could be realized within two cycles and stable CAI combustion was in turn obtained. Due to the high temperature of burnt gas from SI mode, first CAI combustion was advanced and the in-cylinder peak pressure appeared near the TDC.更多还原