一种新的燃烧方式——均匀充量压缩着火的研究进展

分析均质充量压缩着火的特点,国外将均质充量压缩着火方式应用于往复式发动机中的研究现状,阐述燃料系统的设计,并探讨在我国开展均质充量压缩着火研究工作的必要性和方案。     

一种新的燃烧方式——均匀充量压缩着火的研究进展

本文分析了均质充量压缩着火的特点，国外将均质充理压缩着火方式应用于往复式发动机中的研究现状，阐述了燃料系统的设计，并探讨了在我国开展均质充量压缩着火研究工作的必要性和方案。     

在直喷式柴油机上进行HCCI新概念燃烧的探索研究

从形成均匀预混合气及着火后具有良好化学反应动力学效应的角度出发,在单缸135直喷式柴油机上采用双收口型燃烧室、P型喷油泵、预喷射、伞喷油嘴、乳化柴油及乙醇柴油等方法,对实现均质充量压缩着火(homogeneous charge compression ignition,HCCI)燃烧的多种途径进行了对比试验。结果表明:应用伞喷油嘴有效促进了着火前缸内均质预混合气的形成,具有进一步在小排量增压中冷、高压电喷柴油机上推广的潜力;通过燃料设计可控制着火在上止点附近并提高燃烧速率,有利于实现高效、低排放的近似等压预混合燃烧方式。     

车用动力环保节能新技术分析

分析和研究近几年来为适应环保和节能需要而发展的车用发动机在汽油直喷燃烧（GDI）技术、柴油机高压共轨电子控制燃油喷射技术、均质充量压缩点火（HCCI）燃烧技术和代用清洁燃料等几方面取得的技术进展和尚未解决的问题。     

二次燃料喷射正时对发动机性能影响的试验

研究了燃料二次喷射正时对以乙醇、甲醇和汽油混合燃料的准均质充量压燃直喷发动机燃烧和排放性能的影响.结果表明:均质充量压燃发动机的燃烧质量、排放性能可以直接进行控制,并且发动机工况区间也可以利用二次燃料喷射正时来扩展;随着二次喷射正时的延迟,着火时刻被推迟;与纯汽油燃料相比,低当量的混合燃料利用二次燃料喷射正时的优化,可以获得良好的燃烧性能、较低的氮氧化物、未燃烧碳氢化合物与一氧化碳的排放、较高的指示平均有效压力和较高的指示效率;同时,对试验所用燃料而言,二次燃料喷射正时都可以缓解氮氧化物与碳烟排放之间的矛盾.     

二甲醚均质压缩燃烧的数值模拟研究

采用最新的二甲醚(DME)化学动力学反应机理(DME氧化机理包括399个基元反应,涉及79种组分),利用LawrenceLivermore国家实验室开发的HCT软件,进行DME均质充量压燃着火过程的变参数研究。从理论上分析讨论进气温度、进气压力、燃空当量比、发动机转速对燃烧的影响。研究结果表明:DME的均质充量压燃(HCCI)燃烧过程有明显的两阶段,进气温度、进气压力、燃空当量比和发动机转速等参数的改变都会导致DME均质压缩燃烧过程的变化。     

基于可变技术的均质充量压缩着火燃烧控制

均质充量压缩着火(HCCI)是目前发动机领域的研究热点之一。通过分析可变技术对HCCI着火燃烧相位控制的原理及其国内外的研究进展,为实现HCCI成功应用及扩大HCCI功率及转速范围探寻切实可行的方案。分析表明,综合利用可变技术是在更大范围内实现HCCI稳定燃烧、扩大HCCI燃烧功率输出的主要发展方向。     

天然气发动机的研究现状

天然气能降低发动机的有害物排放,是一种比较理想的发动机代用燃料。稀燃天然气发动机具有较高的热效率和较低的NOx排放。均质充量压缩着火(HCCI)燃烧也是提高稀燃天然气发动机热效率的方法之一,并有很低的NOx排放。本文综述了稀燃天然气发动机和HCCI天然气发动机的研究进展,尤其是燃烧室形状、点火系统、充量分层、加氢等对天然气发动机性能的影响及天然气HCCI发动机的燃烧与排放特点。     

柴油喷射压力对HCII燃烧过程影响的可视化

均质混合气引燃(HCII)的燃烧方式融合了柴油机与汽油机的优点,具有提高发动机指示热效率、改善排放的潜力.通过光学发动机,采用高速摄影和燃烧分析系统,研究纯柴油(缸内直喷)与汽油均质混合气柴油引燃两种工作模式下柴油喷射压力对燃烧特性的影响.结果表明:随着柴油喷射压力的提高,两种燃烧模式的燃油雾化质量改善,滞燃期缩短,着火时刻提前,缸内压力和放热率峰值增大,峰值位置提前,同时着火面积增大,燃烧速率加快.在相同柴油喷射压力下,HCII燃烧模式的着火点较为分散,着火时刻相比纯柴油更早,但火焰发展初期速度较慢.纯柴油模式在各喷射压力下均有扩散燃烧特征,中、高喷射压力时扩散燃烧现象更加明显,HCII燃烧模式在低喷射压力下为预混合燃烧和扩散燃烧共存.中等喷射压力下,视窗内分布大片蓝色火焰,着火面积较大,为典型的预混燃烧.高喷射压力下,前期燃烧主要为汽油均质混合气的预混燃烧,放热率峰值点之后以柴油的扩散燃烧为主.     

微动力装置均质催化压燃过程的模拟

基于甲烷气相反应化学动力学机理,耦合甲烷在铂(Pt)表面催化反应机理对微型自由活塞式动力装置带有催化燃烧的均质充量压缩燃烧(HCCI)过程进行数值模拟研究,实现了自由活塞运动与燃烧过程耦合的计算方法.在此基础上对微燃烧室底部添加催化剂的模型与未添加催化剂的模型模拟结果进行了对比.根据H2O2质量分数变化曲线定义了微自由活塞动力装置开始着火时段.通过数值模拟发现,催化燃烧可以使着火时刻提前,压缩比减小,滞燃期缩短,燃料燃烧产生能量的使用效率提高,拓宽微自由活塞压缩均质混合气着火界限;而且得到了催化作用对微燃烧室内温度、压力等因素的影响情况.结果表明:催化作用可以降低微燃烧室内最高燃烧压力及最大压力升高率,从而降低微自由活塞动力装置运行粗暴性,使工作过程平稳.     

基于缸内分段直喷和负气门重叠角汽油机的HCCI燃烧

利用发动机热力循环软件BOC9ST耦合嵌入详细化学反应动力学机理的CHEMKIN代码建立了GDI-HCCI 发动机燃烧数值模型,对缸内直喷汽油机采用分段燃油喷射配合负气门重叠角控制缸内混合气化学组分、混合气浓度及温度历程的策略进行了实验验证及模拟分析．结果显示,加大负气门重叠角以及在此期间喷油可以产生燃油改质效果,缸内温度升高,使HCCI着火更容易控制．由此在保证NOx排放极低的同时循环波动明显减小,负荷稀限拓宽,燃油经济性改善．     

用汽油和甲醇燃油分层拓展HCCI燃烧高负荷的试验研究

在一台单缸HCCI发动机上研究了进气道喷射汽油缸内喷射甲醇形成汽油甲醇燃油分层的HCCI燃烧排放特性,探索了其拓展HCCI燃烧高负荷的潜力。试验结果表明:在汽油HCCI燃烧中喷射甲醇能够有效降低缸内混合气的温度,推迟着火时刻,延长燃烧持续期,从而降低压力升高率和缸内最高燃烧压力,有利于拓展HCCI燃烧高负荷。一定的HCCI负荷工况存在最佳的汽油甲醇比例,且汽油甲醇最佳比例随着负荷的增加不断减小。在最大压力升高率0.5MPa/°CA和较高的指示效率的限制下,自然吸气条件下采用汽油和甲醇燃油分层的HCCI燃烧最高负荷比汽油HCCI燃烧提高了近50%,达到0.62MPa。     

Active fuel design—A way to manage the right fuel for HCCI engines

Homogenous charge compression ignition (HCCI) engines feature high thermal efficiency and ultralow emissions compared to gasoline engines. However, unlike SI engines, HCCI combustion does not have a direct way to trigger the in-cylinder combustion. Therefore, gasoline HCCI combustion is facing challenges in the control of ignition and, combustion, and operational range extension. In this paper, an active fuel design concept was proposed to explore a potential pathway to optimize the HCCI engine combustion and broaden its operational range. The active fuel design concept was realized by real time control of dual-fuel (gasoline and n-heptane) port injection, with exhaust gas recirculation (EGR) rate and intake temperature adjusted. It was found that the cylinderto- cylinder variation in HCCI combustion could be effectively reduced by the optimization in fuel injection proportion, and that the rapid transition process from SI to HCCI could be realized. The active fuel design technology could significantly increase the adaptability of HCCI combustion to increased EGR rate and reduced intake temperature. Active fuel design was shown to broaden the operational HCCI load to 9.3 bar indicated mean effective pressure (IMEP). HCCI operation was used by up to 70% of the SI mode load while reducing fuel consumption and nitrogen oxides emissions. Therefore, the active fuel design technology could manage the right fuel for clean engine combustion, and provide a potential pathway for engine fuel diversification and future engine concept.     

变配气正时对HCCI燃烧的影响研究

试验研究了变进排气正时对缸内早喷柴油均质充量压燃燃烧(HCCI)的影响。柴油在排气上止点附近喷入缸内,研究改变进排气门负重叠期对HCCI燃烧放热率、排放及综合性能的影响。试验研究结果表明,增大气门负重叠期,有利于早喷燃油的快速蒸发和均质混合气的形成,有利于减少柴油湿壁,但是容易使燃烧相位提前,易于产生爆振。增加气门负重叠期,HCCI燃烧的运行范围向低工况扩展,但是中高负荷受到限制。在HCCI燃烧可运行范围内,有害排放产物和指示油耗均下降。     

Characteristics and energy distribution of modulated multi-pulse injection modes based diesel HCCI combustion and their effects on engine thermal efficiency and emissions

Cycle fuel energy distribution and combustion characteristics of early in-cylinder diesel homogenous charge compression ignition (HCCI) combustion organized by modulated multi-pulse injection modes are studied by the engine test. It is found that heat loss due to unburned fuel droplets and CO emission can be decreased effectively by injection mode regulation, and thermal efficiency can be potentially increased by 4%–12%. From the analyses of combustion process, it is also found that diesel HCCI combustion is a process with a finite reaction rate and is very sensitive to injection timing and injection mode. At injection timing of −90°CA ATDC, extra low NO_x emissions can be obtained along with high thermal efficiency. __________ Translated from Transactions of CSICE, 2006, 24(6): 385–393 [译自: 内燃机学报]     

均质压燃燃烧闭环控制系统的开发和试验研究

以缸内喷射CO2为控制手段,实现了对柴油均质压燃(HCCI)燃烧的闭环控制。开发了基于循环的燃烧相位闭环控制系统,试验研究了系统的开环和闭环性能。基于循环的燃烧闭环控制系统包括气缸压力采集、燃烧特征参数计算和控制参数更新等模块。经过对最高燃烧压力对应的曲轴转角(φpmax)、最大压力升高率对应的曲轴转角(φλmax)和燃烧分数为50%时对应的曲轴转角(CA50)等参数的比较,决定选择CA50作为反馈参数。试验结果表明:用CO2喷射作为执行器能实现燃烧相位的快速控制。系统能很好地跟踪CA50阶跃输入,并且在转速和负荷干扰存在的情况下实现对CA50的控制。     

Experimental study of fuel stratification for HCCI high load extension

Fuel stratification has the potential to extend the high load limits of homogeneous charge compression ignition (HCCI) combustion by improving the control over the combustion phase as well as reducing the maximum rate of pressure rise. In this work, experiments were carried out on a single-cylinder engine equipped with a dual-fuel-injection system – a port injector for preparing a homogeneous charge and a direct in-cylinder injector for creating the desired fuel stratification. The homogeneous charge was prepared using gasoline fuel while the fuel stratification was created with the in-cylinder injection of either gasoline or methanol during the compression stroke. The test results indicate that high load extension using gasoline for fuel stratification is limited by the trade-off between CO and NO_x emissions. Weak gasoline stratification leads to an advanced combustion phase and an increase in NO_x emission, while increasing the stratification with a higher quantity of gasoline direct injection, results in a significant deterioration in both the combustion efficiency and the CO emission. Engine tests using methanol for the stratification retarded the ignition timing and prolonged the combustion duration, resulting in a substantial reduction in the maximum rate of pressure rise and the maximum cylinder pressure – a prerequisite for HCCI high load extension. Further tests were then conducted with methanol stratification to extend the HCCI load limit and to optimize the stratified methanol-to-gasoline fuel ratio. Compared to gasoline HCCI, a 50% increase in the maximum IMEP attained was achieved with an acceptable maximum pressure rise rate of 0.5 MPa/°CA while maintaining a high thermal efficiency.     

Dilution limits of n-butane/air mixtures under conditions relevant to HCCI combustion

The role of a spark discharge in extending the operating limits of homogeneous change compression ignition (HCCI) combustion has been investigated using engine experiments and computational flame modeling. The flammability limits of ultra-dilute n-butane/air mixtures are calculated over ranges of temperature, pressure, and dilution levels relevant to HCCI operation. The results suggest that with the elevated temperatures required to achieve HCCI combustion the in-cylinder charge is capable of supporting a propagating flame over most of the HCCI operating regime. However, under light-load and idle conditions the dilution levels are too large and the spark has no effect on HCCI combustion. Thus, some other mechanism must be found to control combustion phasing under these conditions. Since the true eigenvalue for the flame propagation calculation is the mass burning rate and not the flame speed, these results demonstrate that using an arbitrary flame speed cut-off criteria for determining the dilution limit significantly underestimates the actual flammability ranges.     

Experimental study of combustion and emission characteristics of ethanol fuelled port injected homogeneous charge compression ignition (HCCI) combustion engine

The homogeneous charge compression ignition (HCCI) is an alternative combustion concept for in reciprocating engines. The HCCI combustion engine offers significant benefits in terms of its high efficiency and ultra low emissions. In this investigation, port injection technique is used for preparing homogeneous charge. The combustion and emission characteristics of a HCCI engine fuelled with ethanol were investigated on a modified two-cylinder, four-stroke engine. The experiment is conducted with varying intake air temperature (120–150 °C) and at different air–fuel ratios, for which stable HCCI combustion is achieved. In-cylinder pressure, heat release analysis and exhaust emission measurements were employed for combustion diagnostics. In this study, effect of intake air temperature on combustion parameters, thermal efficiency, combustion efficiency and emissions in HCCI combustion engine is analyzed and discussed in detail. The experimental results indicate that the air–fuel ratio and intake air temperature have significant effect on the maximum in-cylinder pressure and its position, gas exchange efficiency, thermal efficiency, combustion efficiency, maximum rate of pressure rise and the heat release rate. Results show that for all stable operation points, NO_x emissions are lower than 10 ppm however HC and CO emissions are higher.     

废气再循环和进气加热实现汽油机HCCI燃烧的性能对比

废气再循环和进气加热是实现汽油机HCCI燃烧的两种不同方式,其对HCCI燃烧性能的影响也不同,为此,在同一台汽油机上分别采用废气再循环和进气加热实现HCCI燃烧,并分析了其在HCCI燃烧性能上存在差异的机理.试验结果表明,相对于进气加热,废气再循环的工质比热容高,但由于稀释比较小,使得其工质总热容反而低,从而缸内燃烧温度高.废气再循环HCCI燃烧的未燃HC排放比进气加热的排放值低41%～59%;NOx排放是后者的2～20倍;而CO排放与负荷有关;其燃烧效率比进气加热HCCI的值高0.8%～14%.然而,由于进气加热的PMEP低,缸内工质比热比大,传热损失小,最终使得进气加热HCCI燃烧的ISFC比废气再循环HCCI燃烧的值低6.6%～16.4%.