异丁醇/辛酸甲酯混合燃料预混层流火焰速度的研究

针对生物柴油与醇类混合燃料燃烧机理研究的需求,采用高速纹影光学诊断方法和定容燃烧弹系统试验研究了异丁醇/辛酸甲酯混合燃料的预混层流燃烧特性。测量了不同当量比和初始压力条件下的不同配比混合燃料—空气预混合气的层流燃烧火焰速度,火焰拉伸率以及马克斯坦长度。分析了燃烧初始条件及异丁醇掺混比例对混合燃料的无拉伸层流燃烧速度及火焰不稳定性的影响规律。结果表明:异丁醇/辛酸甲酯混合燃料的拉伸层流火焰传播速度和层流火焰燃烧速度随着当量比的增加先增加后减少,随着初始压力的增加而减小;马克斯坦长度随着当量比和初始压力的增加而减小;异丁醇掺混比例的增加加快了层流火焰燃烧速度,但使得火焰的不稳定性倾向增加。     

定容燃烧室有无废气稀释燃烧特性实验研究

研究了甲醇燃料在有、无废气稀释情况下的燃烧特性，采用定容燃烧室进行实验，并利用激光纹影技术和高速摄影机对火焰图像进行可视化，研究了不同燃烧初始压力、不同化学当量比和废气稀释情况下的燃烧时间和火焰传播情况。结果表明，在贫燃料状态，当化学当量比增大时，燃烧时间明显缩短，在废气稀释情况下，燃烧时间延长，在高初始燃烧压力时，火焰传播速度下降更明显。同时，采用图像技术可以获得初始压力变化和废气稀释情况下非常有用的火焰结构信息。实验表明，当燃烧时间较长时，定容燃烧过程要考虑浮升力的影响。     

不同初始压力下氢气燃烧的胞状不稳定性及自加速性

采用高速纹影摄像系统和定容燃烧弹对不同初始压力下(0.1~0.5,MPa)氢气燃烧的不稳定性和自加速性进行了实验研究,分析了火焰胞状不稳定性的发展过程和变化规律,分别对比了火焰轮廓及火焰传播速度的自加速表现.研究结果表明,在火焰没有达到一开始就完全胞状化之前,随初始压力的增大,氢气燃烧的不稳定性增强;胞状不稳定的火焰会出现自加速,而稳定火焰不会出现自加速;火焰的加速特性在均布的胞状结构形成后便会出现,其始点与胞状不稳定的火焰临界半径一致,始点过后,火焰的传播速度(或燃烧速度)随着燃烧半径的增加(或燃烧时间的增加)而不断地自加速.     

二乙醚-空气预混合气层流燃烧速率测定

在定容燃烧弹内利用高速纹影摄像法系统地研究了不同初始压力、不同初始温度和不同燃空当量比下二乙醚-空气预混合气的层流燃烧特性。利用球形发展火焰分析得到了不同初始压力、不同初始温度和不同燃空当量比下二乙醚-空气预混合气的无拉伸层流火焰燃烧速率、马克斯坦长度等层流燃烧参数。研究结果表明:无拉伸层流火焰燃烧速率随初始温度的增加而增加,随初始压力的增加而降低;马克斯坦长度随着初始温度的增加而减小,随初始压力的增加而减小,随当量比的增加而减小,表明火焰前锋面不稳定性随初始温度和初始压力的增加而增加,随混合气浓度的增加而增加。基于试验数据获得了二乙醚-空气预混合气无拉伸层流燃烧速率的关系式。     

电增压及EGR共同作用下对降低汽油机燃油消耗率的试验研究

基于光学定容燃烧弹试验平台,通过高速纹影摄像系统在相同甲烷燃料初始温度、压力及混合气浓度下,定量分析了不同结构预燃室湍流射流点火（turbulent jet ignition, TJI）的燃烧特性,包括火焰传播速度、火焰面积、火焰形态及燃烧压力等参数。研究结果表明,预燃室孔径越小,相同时间内火焰传播得越远,火焰传播速度和火焰面积增长速度越快,燃烧压力峰值越高。随着预燃室孔径减小,着火机理会由射流中带有火焰的火焰点火转变为火焰过孔时熄灭的喷射点火。喷射点火着火时刻延迟,初始火焰速度减慢,但燃烧压力峰值受影响不大。多级加速预燃室压力升高率与压力峰值与单孔预燃室相比变化不大。虽然火焰出口时速度较慢,但是火焰出口时刻提前且速度衰减较弱,因此多级加速预燃室火焰速度在短时间内超过单孔预燃室,并且压力和火焰面积也更早达到最大值。     

不同预燃室结构对甲烷湍流射流点火燃烧的影响

基于光学定容燃烧弹试验平台,通过高速纹影摄像系统在相同甲烷燃料初始温度、压力及混合气浓度下,定量分析了不同结构预燃室湍流射流点火(turbulent jet ignition,TJI)的燃烧特性,包括火焰传播速度、火焰面积、火焰形态及燃烧压力等参数。研究结果表明,预燃室孔径越小,相同时间内火焰传播得越远,火焰传播速度和火焰面积增长速度越快,燃烧压力峰值越高。随着预燃室孔径减小,着火机理会由射流中带有火焰的火焰点火转变为火焰过孔时熄灭的喷射点火。喷射点火着火时刻延迟,初始火焰速度减慢,但燃烧压力峰值受影响不大。多级加速预燃室压力升高率与压力峰值与单孔预燃室相比变化不大。虽然火焰出口时速度较慢,但是火焰出口时刻提前且速度衰减较弱,因此多级加速预燃室火焰速度在短时间内超过单孔预燃室,并且压力和火焰面积也更早达到最大值。     

初始压力对天然气-氢气-空气混合气火焰传播特性的影响

使用定容燃烧弹研究了不同初始压力下天然气-氢气-空气混合气的火焰传播规律,得到了初始压力、掺氢比和燃空当量比对无拉伸层流燃烧速率、质量燃烧流量的影响,结合高速纹影图片分析了影响火焰稳定性的因素(马克斯坦长度、火焰面两侧密度比和火焰厚度).结果表明,掺氢天然气无拉伸层流燃烧速率以及火焰的不稳定性受掺氢比、初始压力和燃空当量比的综合影响.结合高速纹影图片,得出火焰的稳定性会随初始压力的增加而减小;在相同的燃空当量比和掺氢比下,初始压力对密度比的影响不大,但是对火焰厚度的影响比较明显.     

氢气/空气混合气层流燃烧速度的实验测量与模拟计算

采用高速纹影系统和定容燃烧弹对氢气预混层流燃烧球形膨胀火焰的燃烧速度特性进行研究.分别在改变燃空当量比(0.3～6.0)、初始温度(300～450 K)、初始压力(0.1～ 0.3 MPa)的条件下,对比分析Markstein长度、火焰传播速度、火焰燃烧速度的变化规律,得出了燃烧速度随燃空当量比、温度、压力变化的拟合公...     

掺氢对微尺度空间内预混层流火焰转捩爆燃特性的影响

针对基于燃烧的微小型动力装置存在燃烧效率低、火焰传播速度慢的问题,设计了一个可视化的、特征间距仅为0.45 mm的微尺度定容燃烧室,实验比较了0～1的掺氢比例下,丙烷/氢气/空气预混火焰在该燃烧室内的传播以及加速过程.实验发现没有掺氢时,丙烷/空气预混火焰需要在0.25 MPa初始压力下才能够传播;当掺氢比例为0.2时...     

甲醇-空气-氮气混合气预混球型火焰的试验研究

利用高速纹影摄像法在定容燃烧弹内研究了不同燃空当最比、初始压力、初始温度和气体稀释度下甲醇-空气-氮气混合气预混球型火焰的发展特性以及3种火焰锋面的不稳定性.获得了不同初始状态下的层流燃烧速度、质量燃烧流量和马克斯坦长度.高的初始压力时,火焰锋面生成的裂纹发展并形成细胞状结构.稀混合气时,浮力和电极的冷却作用对火焰的发展有重要影响.当量比在化学计量比附近时,随着初始温度的提高,流体动力学不稳定性被抑制.随着初始压力的增加,流体动力学不稳定性增强.稀释气的加入抑制了火焰锋面流体动力学的不稳定性.     

Effects of initial pressure and hydrogen concentration on laminar combustion characteristics of diluted natural gas–hydrogen–air mixture

In this study, the experiment study about the laminar burning velocity and the flame stability of CO₂ diluted natural gas–hydrogen–air mixture was conducted in a constant volume combustion vessel by using the high-speed schlieren photography system. The unstretched laminar burning velocity and the Markstein length at different hydrogen fractions, dilution ratios and equivalence ratios and with different initial pressures were obtained. The flame stability was studied by analyzing the Markstein length, the flame thickness, the density ratio and the flame propagation schlieren photos. The results showed that the unstretched laminar burning velocity would be reduced with the increase of the initial pressure and dilution ratio and would be increased with the increase of the hydrogen fraction of the mixture. Meanwhile, the Markstein length would be increased with the increase of the equivalence ratio and the dilution ratio. Slight flaws occurred at the early stage. At a specific equivalence ratio, a higher initial pressure and hydrogen fraction would cause incomplete combustion.     

初始温度对氢-空气预混诱导湍流燃烧特性的影响

通过在火焰传播路径上布置孔板实现诱导湍流燃烧,利用纹影技术和压力采集系统研究了初始温度对孔板诱导氢-空气预混湍流燃烧特性的影响。试验结果表明:穿越孔板前火焰传播速度略有下降,穿越孔板后火焰被诱导为湍流燃烧,火焰发展进程加快;随着初始温度的升高,最高燃烧压力和最大压升率减少,两者出现的时刻提前,添加孔板后的燃烧持续期变化率降低,但穿越孔板后的火焰传播速度的差异不显著。     

Experimental study on induced accelerated combustion of premixed hydrogen-air in a confined environment

The study on induced accelerated combustion of premixed hydrogen-air in a confined environment is of great significance for the efficient utilization of hydrogen energy in internal combustion engines. The accelerated flame induced by the orifice plate is more stable and easy to control, which is beneficial to achieve controlled and rapid turbulent combustion. In this work, the accelerated combustion process induced by the orifice plate, and the influence of the orifice structure and initial conditions on the flame propagation and combustion characteristics were investigated by constant volume combustion bomb and schlieren method. The results show that the combustion process induced by the orifice plate consists of three stages: the initial stage of propagation, the accelerated stage of the orifice plate, and the end combustion stage. The reduction in aperture induces greater turbulence intensity and increases the perturbation of the orifice plate to the flame, resulting in a substantial increase in flame propagation speed through the orifice plate. As the initial pressure and the equivalence ratio increase, the velocity of turbulent flame induced by the orifice plate and the change rate of the velocity before and after the orifice plate increase. As the initial temperature increases, the turbulent flame propagation velocity does not change much, and the velocity change rate before and after the orifice plate decreases. The effect of the initial conditions on flame acceleration induced by the orifice plate is essentially the influence of flame propagation speed and instability. The greater the flame propagation speed and the stronger the flame instability, the stronger the induced turbulence and the greater the influence of the turbulent flow disturbance, and the greater the velocity of the turbulent flame induced by the orifice plate. There exists an optimum aperture for the shortest combustion duration at any initial conditions, but the optimal diameter is not sensitive to changes in initial conditions. The effect of orifice-induced combustion acceleration is remarkable, and the combustion durations induced by each orifice plate are shortened by more than 50%.     

Effect of initial pressure on flame–shock interaction of hydrogen–air premixed flames

By utilizing a newly designed constant volume combustion bomb (CVCB), turbulent flame combustion phenomena are investigated using hydrogen–air mixture under the initial pressures of 1 bar, 2 bar and 3 bar, including flame acceleration, turbulent flame propagation and flame–shock interaction with pressure oscillations. The results show that the process of flame acceleration through perforated plate can be characterized by three stages: laminar flame, jet flame and turbulent flame. Fast turbulent flame can generate a visible shock wave ahead of the flame front, which is reflected from the end wall of combustion chamber. Subsequently, the velocity of reflected shock wave declines gradually since it is affected by the compression wave formed by flame acceleration. In return, the propagation velocity of turbulent flame front is also influenced. The intense interaction between flame front and reflected shock can be captured by high-speed schlieren photography clearly under different initial pressures. The results show that the propagation velocity of turbulent flame rises with the increase of initial pressure, while the forward shock velocities show no apparent difference. On the other hand, the reflected shock wave decays faster under higher initial pressure conditions due to the faster flame propagation. Moreover, the influence of initial pressure on pressure oscillations is also analyzed comprehensively according to the experimental results.     

Effect of initial pressure,temperature and equivalence ratios on laminar combustion characteristics of hydrogen enriched natural gas

In this study, the flame propagation characteristics of premixed natural gas–hydrogen–air mixtures were studied in constant volume combustion bomb by using the high-speed schlieren photography system. The flame radius, laminar flame propagation speed and the flame stretch rate were obtained under different initial pressure, temperature, equivalence ratios and hydrogen fractions. Meanwhile, the flame stability and their influencing factors were obtained by analyzing the Markstein length and the flame propagation schlieren photos under various combustion conditions. The results show that the stretched laminar propagation speed increases with the increase of the initial temperature and hydrogen fraction of the mixture, and will decreases with the increase of the initial pressure. Meanwhile, according to the Markstein length and the flame propagation pictures, the flame stability decreases with the increase of the temperature and hydrogen fraction, and the slight flaws occurred at the early stage; at larger flame radius, the flame stability is more sensitive to the variation of the initial temperature and hydrogen fraction than to that of initial pressure and equivalence ratio.     

应用高速纹影法对汽油机燃烧过程的研究

根据光学纹影法的基本原理和高速摄影技术,在可视化发动机台架上搭建了一套反射式纹影光路系统,使其能够较清晰准确地记录燃料初期蓝焰的扩散过程。通过对比,纹影图像比直接摄影图像能更早地观察到火焰的产生,火焰轮廓更大,能够反应火焰的变化形态。试验将此系统应用在汽油机燃烧过程的研究中,并分析了空燃比和负荷时汽油机火焰传播速度及火焰形态的影响。结果表明:在理论空燃比附近,随着混合气变浓,着火始点靠前,火焰传播速度加快,火焰的表面皱折变大;负荷的提高使得燃烧更加充分,着火提前,火焰传播速度提高,火焰皱折增大。     

Measurements of laminar burning velocities and Markstein lengths for methanol-air-nitrogen mixtures at elevated pressures and temperatures

The laminar burning velocities and Markstein lengths for the methanol-air mixtures were measured at different equivalence ratios, elevated initial pressures and temperatures, and dilution ratios by using a constant volume combustion chamber and high-speed schlieren photography system. The influences of these parameters on the laminar burning velocity and Markstein length were analyzed. The results show that the laminar burning velocity of the methanol-air mixture decreases with an increase in initial pressure and increases with an increase in initial temperature. The Markstein length decreases with an increase in initial pressure and initial temperature, and increases with an increase in the dilution ratio. A cellular flame structure is observed at an early stage of flame propagation. The transition point is identified on the curve of flame propagation speed against stretch rate. The reasons for the cellular structure development are also analyzed.     

Flame front evolution and laminar flame parameter evaluation of buoyancy-affected ammonia/air flames

For flames with very low burning speed, the flame propagation is affected by buoyancy. Flame front evolution and laminar flame parameter evaluation methods of buoyancy-affected flame have been proposed. The evolution and propagation process of a center ignited expanding ammonia/air flame has been analyzed by using the methods. The laminar flame parameters of ammonia/air mixture under different equivalence ratio (ER) and initial pressure have been studied. At barometric pressure, with the increase of ER, the laminar burning velocity (LBV) of ammonia/air mixture undergoes a first increase and then decrease process and reaches its maximum value of 7.17 cm/s at the ER of 1.1, while the Markstein length increases monotonously. For ammonia/air flames with ER less than unity, the flame velocity shows a decreasing trend with stretch rate, resulting in the propensity to flame instability, but no cellular structure was observed in the process of flame propagation. As the initial pressure increases, the LBV decreases monotonously as well as the Markstein length. The flame thicknesses of ammonia/air mixtures decrease with initial pressure and are much thicker than those of hydrogen flames, which makes a stronger stabilizing effect of curvature on the flame front. The most enhancement of LBV is contributed by the dehydrogenation reaction of NH₃ with OH. The NO concentration decreases significantly with the increase of ER.     

Experimental study of flame propagation across a perforated plate

Flame propagation across a single perforated plate was experimentally studied in a square cross-section channel. Experiments were performed in premixed hydrogen-air mixture with different equivalence ratios and initial pressures, aiming at identifying the parametric influence. High-speed schlieren photography and pressure records were used to capture the flame front and obtain the pressure build-up. Four stages for the flame front crossing the perforated plate were obtained, namely, laminar flame, jet flame, turbulent flame and secondary flame front. Following ignition, a laminar flame was obtained, which was nearly not affected by the confinement. This laminar flame was squeezed to pass through the perforated plate, producing the jet flame with a step change on velocity. Turbulent flame was generated by merging the jets, which facilitated the acceleration of the flame front. Secondary flame front induced by Rayleigh-Taylor instability was clearly observed in the process of the turbulent front moving forward. Both velocity and pressure are enhanced in this stage. Parametric studies suggested that the secondary flame front is more obvious in the stoichiometric mixture with higher initial pressure, and characterized by a faster propagation velocity and a bigger pressure rise.