乙醇-正庚烷燃料均质压缩过程着火与燃烧特性的研究

详细研究了乙醇正庚烷混合燃料实现均质充量压缩过程的自燃着火特性和燃烧特性。在单缸HCCI发动机上，开展了正庚烷、10％～50％乙醇正庚烷燃料在1800r／min下不同负荷时的试验研究。研究表明，在正庚烷中加入30％～40％比例的乙醇，HCCI运行的平均指示压力可以从0．34MPa拓展到0．52MPa，大负荷下的指示热效率达到50％，但低负荷热效率显著降低。由于乙醇较高的辛烷值，随燃料中乙醇比例的增加，低温反应明显推迟，发生低温反应的起始温度相应升高，峰值放热率降低，并且当乙醇比例达到50％以后，观察不到明显的低温反应。由此导致高温着火时刻推迟，燃烧持续时间延长。正庚烷、10％～30％乙醇正庚烷的HC较低，但是乙醇比例达到40％后，HC显著升高。CO排放在平均指示压力0．15～0．25MPa最高，负荷增加后得到改善。在供给相同的循环热量条件下，随乙醇比例增加，最大燃烧压力以及对应时刻、着火时刻都呈现明显的变动。     

甲基叔丁基醚对正庚烷均质压缩燃烧抑制效果的试验研究

研究了含甲基叔丁基醚(MTBE)的正庚烷HCCI燃烧特性和排放影响因素.在单缸HCCI发动机上,开展了正庚烷、10%～50%MTBE正庚烷燃料在1 800 r/min下不同负荷时的试验研究.研究表明,在正庚烷中加入MTBE后,低温反应时刻明显推迟,低温峰值放热率降低,负温度系数区持续时间延长,引起高温反应时间的推迟,从而使得最大平均指示压力(IMEP)增加,但是最小稳定运行IMEP也增加,燃烧效率相对降低.对影响HC和CO排放的参数分析发现,影响HC排放的主要参数是最高燃烧温度和燃料成分;而影响CO的参数主要有最高燃烧温度、最大压力升高率和平均指示压力.要保持较低的CO排放,最高燃烧温度要大于1 500 K,最大压力升高率高于0.5 MPa/°CA,平均指示压力大于0.3 MPa,燃烧持续时间小于9°CA.     

含异丙醇添加剂的HCCI燃烧特性及其排放影响因素

研究了异丙醇作为添加剂对正庚烷HCCI燃烧的抑制效果,分析了影响HC和CO排放的燃烧参数,考察了EGR对含异丙醇添加剂的HCCI燃烧和排放的影响.在单缸HCCI发动机上,开展了正庚烷、10%~60%异丙醇/正庚烷燃料(体积比)在1 800 r/min下不同负荷时的试验研究.研究表明,在正庚烷中加入异丙醇后,低温反应时刻明显推迟,低温峰值放热率降低,引起高温反应时间的推迟,从而使得最大平均指示压力增加,但是最小稳定运行平均指示压力也增加,燃烧效率相对降低.对影响HC和CO排放的参数分析发现,影响HC排放的主要因素是混合燃料中高十六烷值燃料的比例,而影响CO的参数主要有最高燃烧温度,其他参数如最大压力升高率、平均指示压力、着火时刻也产生一些间接影响.对具有相同循环能量的各种燃料燃烧稳定性的研究表明,10%和20%混合燃料燃烧开始出现一定波动,30%和40%混合燃料循环波动明显,而50%混合燃料就相当恶化了.EGR对含较少异丙醇的混合燃料影响不大,但对40%异丙醇/正庚烷混合燃料的燃烧与排放影响相当显著.     

均质压燃燃烧着火时刻的循环变动

在一台改装单缸机上,研究了进气温度、进气压力、外部废气再循环率等运行参数对汽油均质压燃(HCCI)燃烧着火时刻循环变动的影响.结果表明:着火时刻对应的曲轴转角对HCCI燃烧循环变动有重大影响.着火时刻提前,HCCI燃烧循环变动较小.不同运行参数对燃烧循环变动的影响不同.进气温度和冷却水温度升高、进气压力增大有助于减小着火时刻循环变动,过量空气系数和EGR率增大会增大着火时刻循环变动.     

生物柴油掺烧率对非道路用柴油机燃烧循环变动特性的影响

针对非道路用186FA柴油机掺烧生物柴油燃烧循环变动情况,进行了燃用不同生物柴油掺烧率的试验.根据实测示功图对主要燃烧参数进行了循环变动分析.结果表明:随着生物柴油的掺烧,燃烧始点提前,放热率峰值减小;平均指示压力(pmi)、缸内压力峰值(pmax)、放热率峰值循环变动系数(COV)呈减小的趋势,而其对应相位波动比纯柴油大;最大压力升高率在中低负荷时循环变动显著;平均指示压力与缸内压力峰值和放热率峰值都有很好的对应关系.     

采用快速压缩机对甲醇燃料的HCCI燃烧特性的研究

为进一步了解高辛烷值燃料的均质压燃燃烧特性,利用自主研发的快速压缩机,研究了边界条件对甲醇燃料HCCI燃烧特性的影响.试验表明:随着充量温度的升高,燃烧始点提前,燃烧持续期缩短,燃烧温度最大值增加,放热率最大值增加,最大压力升高率增大,最大压力升高率出现时刻提前;随着可燃混合气过量空气系数的增加,可燃混合气的浓度减小,燃烧始点延迟,燃料的最高燃烧温度降低,放热率最大值降低,最大压力升高率降低,着火温度升高,同时反应速率减慢,所以燃烧持续期增加,最大压力升高率减小,最大压力升高率出现时刻延迟.     

甲醇替代率对双燃料发动机燃烧及其循环变动的影响

为研究甲醇/柴油双燃料发动机甲醇替代率对燃烧及其循环变动的影响,通过在单缸柴油机上加装进气道甲醇喷射系统,进行了不同甲醇替代率的试验研究。研究表明,随着甲醇替代率增加,缸内着火时刻推迟,放热率双峰现象逐渐消失,放热率峰值、最高燃烧压力和最大压力升高率均增加。甲醇替代率对不同工况下指示热效率的影响不同,低速工况指示热效率随甲醇替代率的增加而降低,高速高负荷工况指示热效率随甲醇替代率的增加而略有增加。不同工况下的排放影响也存在明显差异,随甲醇替代率的增加,低速低负荷工况排放变化较小,而在高速高负荷下排放变化大。甲醇替代率对燃烧循环变动影响表明,低速低负荷循环变动随甲醇替代率增加而明显增加,当替代率增加至28.7%时,峰值压力的循环变动率增加2.5%,峰值压力对应曲轴转角分布也更加分散。     

用快速压缩机研究乙醇燃料的HCCI燃烧特性

为进一步了解乙醇燃料的HCCI燃烧特性,利用自主研发的快速压缩机,研究了边界条件对乙醇燃料HC-CI燃烧特性的影响.试验表明:随着充量温度的升高,燃烧持续期缩短,最高燃烧温度升高,放热率最大值增加,最大压力升高率增大,最大压力升高率出现的时刻提前;随着过量空气系数的增大,可燃混合气的浓度减小,燃烧始点延迟,燃料的最高燃烧温度降低,放热率最大值降低,最大压力升高率降低、出现时刻提前,着火温度降低,同时反应速率减慢,燃烧持续期增加.     

进气喷射不同辛烷值燃料的HCCI燃烧爆震试验分析

HCCI燃烧是化学动力学控制的均匀稀混合气的压缩自燃,大量的浓混合气同时着火燃烧导致燃烧速度过快而爆震。致力于能够描述或量化HCCI爆震程度方法的研究,进而建立HCCI爆震强度评价标准。不同辛烷值掺比燃料在不同工况的HCCI燃烧压力信号的频谱对比分析结果表明：不同辛烷值燃料的HCCI燃烧爆震具有相近的爆震特征频带,其能量集中的主要爆震特征频带位于4～12kHz;确定HCCI燃烧缸压信号在4～12kHz频带处带通滤波的峰值压力Pbps为HCCI爆震强度评价标准,当Pbps日大于0．15MPa,断定HCCI燃烧出现爆震。据此找出不同辛烷值的混合掺比燃料HCCI燃烧的安全运行范围。     

沼气掺氢发动机燃烧稳定性试验

在一台单缸火花点火发动机上开展了燃用不同组分配比的沼气模拟气体的掺氢混合气的燃烧稳定性试验研究.研究结果表明:在15%～35%的掺氢比范嗣内,随着混合气中掺氢比的增加,发动机循环变动变小,燃烧稳定性提高.掺氢导致平均指示压力的循环变动系数减小,燃烧放热率加快,火焰发展期缩短.其中35%掺氢比的混合气比15%掺氢比的混合...     

稀燃天然气发动机燃烧循环变动影响因素研究

通过对一台点燃式多点电喷稀燃天然气发动机进行试验,获得了不同工况下的平均指示压力循环变动系数,以此为基础研究了燃空当量比、节气门开度、转速及点火时刻对稀燃天然气发动机燃烧循环变动的影响趋势。结果表明:混合气燃空当量比越小,燃烧循环变动越明显,当燃空当量比降低到一定值时,平均指示压力循环变动系数的增长会突然加大;节气门开度越小燃烧循环变动越明显,节气门开度小于30%后,其对燃烧循环变动影响更加明显;燃烧循环变动量随转速上升有增加的趋势,在高转速工况下燃烧循环变动的加强尤其明显;在工况一定的条件下存在一个最优的点火时刻可使稀燃天然气发动机的燃烧循环变动最小。     

Experimental investigation on the effect of intake air temperature and air–fuel ratio on cycle-to-cycle variations of HCCI combustion and performance parameters

Combustion in HCCI engines is a controlled auto ignition of well-mixed fuel, air and residual gas. Since onset of HCCI combustion depends on the auto ignition of fuel/air mixture, there is no direct control on the start of combustion process. Therefore, HCCI combustion becomes unstable rather easily, especially at lower and higher engine loads. In this study, cycle-to-cycle variations of a HCCI combustion engine fuelled with ethanol were investigated on a modified two-cylinder engine. Port injection technique is used for preparing homogeneous charge for HCCI combustion. The experiments were conducted at varying intake air temperatures and air–fuel ratios at constant engine speed of 1500 rpm and P-θ diagram of 100 consecutive combustion cycles for each test conditions at steady state operation were recorded. Consequently, cycle-to-cycle variations of the main combustion parameters and performance parameters were analyzed. To evaluate the cycle-to-cycle variations of HCCI combustion parameters, coefficient of variation (COV) of every parameter were calculated for every engine operating condition. The critical optimum parameters that can be used to define HCCI operating ranges are ‘maximum rate of pressure rise’ and ‘COV of indicated mean effective pressure (IMEP)’.     

不同过量空气系数下射流点火发动机燃烧、排放和爆震特性的试验研究

基于单缸试验机研究了过量空气系数对射流点火发动机性能的影响.通过分析发动机性能曲线、缸内燃烧情况及爆震特性探究射流点火最佳运行区间,并与火花点火燃烧方式进行对比.结果表明,射流点火可以有效提升瞬时放热率并拓展发动机稀燃极限,缩短缸内混合气滞燃期与燃烧持续期,同时燃油经济性有一定提升.在稀燃条件下氮氧化物排放极低.爆震方...     

多火花塞点火实现快速燃烧的试验研究

使用快速压缩-膨胀机改装的多火花塞点火试验台架,研究了火花塞数目对指示功大小、最高燃烧压力和最大压升率、燃料放热速率及爆震特性的影响。得到结果如下:液压源压力及混合气浓度相同,点火相位从上止点前5~35mm逐渐增大时,指示功先增大后减少,即存在最佳点火相位;随着火花数目的增加,最佳点火时刻后移;多火花塞点火的放热速率、最高燃烧压力和压升率、指示功均比单火花塞点火有明显提升,提升幅度和火花塞数目并不成线性关系;在混合气稀薄时,多火花塞点火对燃烧速率及指示功的提升作用更加明显;随着液压源压力的增大,相同点火相位时,多火花塞比单火花塞点火爆震倾向更加严重。     

Applying the multi-zone model in predicting the operating range of HCCI engines

In this paper, a multi-zone model is developed to predict the operating range of homogeneous charge compression ignition (HCCI) engines. The boundaries of the operating range were determined by knock (presented by ringing intensity), partial burn (presented by combustion efficiency), and cycle-to-cycle variations (presented by the sensitivity of indicated mean effective pressure to initial temperature). By simulating an HCCI engine fueled with iso-octane, the knock and cycle-to-cycle variations predicted by the model showed satisfactory agreement with measurements made under different initial temperatures and equivalence ratios; the operating range was also well reproduced by the model. Furthermore, the model was applied to predict the operating range of the HCCI engine under different engine speeds by varying the intake temperatures and equivalence ratios. The potential to extend the operating range of the HCCI engine through two strategies, i.e., variable compression ratio and intake pressure boosting, was then investigated. Results indicate that the ignition point can be efficiently controlled by varying the compression ratio. A low load range can be extended by increasing the intake temperature while reducing the compression ratio. Higher intake temperatures and lower compression ratios can also extend the high load range. Boosting intake pressure is helpful in controlling the combustion of the HCCI engine, resulting in an extended high load range.     

Applying the multi-zone model in predicting the operating range of HCCI engines

In this paper, a multi-zone model is developed to predict the operating range of homogeneous charge compression ignition (HCCI) engines. The boundaries of the operating range were determined by knock (presented by ringing intensity), partial burn (presented by combustion efficiency), and cycle-to-cycle variations (presented by the sensitivity of indicated mean effective pressure to initial temperature). By simulating an HCCI engine fueled with iso-octane, the knock and cycle-to-cycle variations predicted by the model showed satisfactory agreement with measurements made under different initial temperatures and equivalence ratios; the operating range was also well reproduced by the model. Furthermore, the model was applied to predict the operating range of the HCCI engine under different engine speeds by varying the intake temperatures and equivalence ratios. The potential to extend the operating range of the HCCI engine through two strategies, i.e., variable compression ratio and intake pressure boosting, was then investigated. Results indicate that the ignition point can be efficiently controlled by varying the compression ratio. A low load range can be extended by increasing the intake temperature while reducing the compression ratio. Higher intake temperatures and lower compression ratios can also extend the high load range. Boosting intake pressure is helpful in controlling the combustion of the HCCI engine, resulting in an extended high load range.     

Effects of direct-injected hydrogen addition on methane combustion performance in an optical SI engine with high compression-ratio

Natural gas is one of the most potential alternative fuel of clean combustion and anti-knocking property. However, slow-burning rate and obvious cyclic variations have become the major concerns for modern gas engines. Based on a high compression-ratio, optically accessible, single-cylinder spark-ignition engine, fundamental experiments were conducted to investigate the role of direct-injected hydrogen under from stoichiometric to lean combustion conditions. Synchronization measurement of in-cylinder pressure and optical flame imaging was conducted to analyze cycle-to-cycle variations, indicated thermal efficiency, and flame evolution. The results show that as the addition of direct-injected hydrogen, the cycle-to-cycle variations decrease and indicated thermal efficiency increases, with advanced combustion phase and shortened combustion duration. The combustion imaging indicates that the significant positive influence is from the direct-injected hydrogen, which promotes initial flame kernel formation and early flame propagation. Further, an empirical criterion for mass fraction burned combined with optical data was adopted for quantification and analysis of early flame evolution. It shows that the addition of direct-injected hydrogen mainly promotes the early-stage flame propagation, manifesting increased the burning rate and thermal efficiency. The results shall give useful information in the application of direct-injected hydrogen to improve natural gas engine performance while increasing flame speed and controlling cyclic variations.     

双燃料发动机的燃烧模型

针对双燃料发动机燃烧特性，建立了柴油喷雾扩散燃烧子模型和气体燃烧均质混合气火焰传播燃烧子模型，应用该模型研究了双燃料发动机燃烧机理，计算结果和实验结果相当吻合。计算表明：当引燃柴油比例较大时，双燃料发动机燃烧过程以喷雾混合控制燃烧为主，柴油喷雾扩散燃烧模型与实测较吻合；当柴油比例较小时，该过程以均质混合气火焰传播燃烧为主，均质混合气火焰传播燃烧模型与实测软吻合。计算结果表明，引燃柴油量对双燃料发动机性能影响较大，引燃柴油减少，着火滞燃期延长，缸内最大爆发压力升高。     

燃烧室压力对燃油喷雾和燃烧的影响研究

采用CHAMKIN模拟分析燃烧过程,基于自行设计的可视化定压燃烧系统试验研究燃烧室压力对燃油喷雾和燃烧的影响。结果表明:随着压力的升高雾化效果逐渐变差;进气旋流可以改善雾化效果;如果进气旋流是高温气体,则改善情况更明显。压力的增加仅加快了反应速率,缩短了着火延迟时间,并没有引起着火过程中温度的很大变化。随着燃烧压力的增加,火焰逐步向燃油喷嘴处移动,可通过提高烟气卷吸率增强气旋效果,使火焰更长,燃烧更均匀,避免烧坏油头及燃烧室内部分温度过高等不良后果。     

废气再循环对二甲醚/天然气双燃料均质压燃燃烧过程和排放特性的影响

在一台单缸直喷式柴油机上研究了冷却废气再循环(EGR)对二甲醚(DME)／天然气(CNG)双燃料均质压燃(HCCI)燃烧过程和排放的影响．结果表明，EGR率加大，着火时刻滞后，放热速率降低，燃烧持续期延长，DME比例加大，着火始点提前，放热率峰值上升，燃烧持续期缩短，EGR率增大，发动机“失火”和爆震燃烧的DME比例增大，但“失火”和爆震燃烧之间的DME比例区间变宽，EGR可以拓宽HCCI发动机的工况范围．对应不同比例的EGR，有一个热效率最佳的DME比例区域．HC排放和CO排放随EGR率的增高而增加，随DME比例的增大而降低．NO。排放在不发生爆震的情况下保持在极低的水平．因此，控制DME比例和EGR率是控制DME／CNG双燃料HCCI发动机燃烧过程、性能和排放的关键。