甲烷/空气典型混合模式在约束空间内的燃烧特性研究

燃料质量浓度分布在一定程度上影响混合气体的燃烧效率,能使燃气充分混合的同轴射流、旋片同轴、轴切结合、切向旋流等典型混合模式在航空发动机、燃气轮机及火箭发动机等先进燃烧技术应用中较为常见。因此,设计了甲烷/空气部分预混的燃烧实验装置,较为系统地实验研究了旋流数和轴向流速对混合气体在约束空间燃烧室内燃烧特性的影响。结果表明：对于有中心射流的混合结构,燃气轴向流速较低时产生黄色火焰,增大轴向流速,黄色火焰转为蓝色湍流火焰,且温度分布趋于均匀;纯切向旋流燃烧器的掺混效果较好,受燃气轴向流速的影响小,火焰结构稳定,均为蓝色火焰,温度轴/径向分布均匀且趋势一致,同当量比下燃烧产物中的污染物体积分数最小。     

The effect of premixed stratification on the wave dynamics of a rotating detonation combustor

Typical injection schemes of rotating detonation combustors inject fuel locally into the combustion channel, creating stratified fuel-rich and fuel-lean mixing regions. In this study, premixed hydrogen and air rotating detonations are explored in a rotating detonation combustor through premixing part of the fuel into the oxidizer flow. The objective is to investigate the effect of premixing on the operation of the combustor. Three premixing schemes are examined where the detonation wave speeds are analyzed. The results show that in premixing, the fuel-lean regions became more favorable for continuous detonation propagation when premixed with the bypass fuel, resulting in higher detonation wave speeds. This phenomenon is shown to be independent of the global fuel-air equivalence ratio and the amount of fuel premixed into the oxidizer. As such, combustor performance and the operational regime could be improved with lean hydrogen premixing amounts in the main flow oxidizer.     

A numerical study on the effects of side-inlet angle on the mixing phenomena in a three-dimensional side-dump combustor

The effects of side-inlet angle on fuel/air mixing phenomena in a three-dimensional side-dump combustor with dual opposite curved side-inlet ducts are numerically investigated in the present paper. The integral computational domain, including side-inlet ducts as well as the cylindrical combustion chamber itself, are used to resolve the complete flow fields. The side-inlet angle is varied as 30°, 60° and 90° to examine its effects on the flow fields and fuel/air mixing phenomena. The results exhibit that the important flow features in the side-dump combustor, including the recirculation structures and secondary flow motions, are all significantly influenced by the side-inlet angle. The effects of side-inlet angle on the fuel distributions in the side-inlet duct and cylindrical combustion chamber are also presented in the current study, which provides worthwhile information for the combustor design work.     

Influence of coaxial air jet on mass diffusion of hydrogen jet injected through lobe-injector at supersonic flow

The technique of fuel injection in the combustion chamber is crucial for increasing the performance of hypersonic vehicles. This study tries to investigate the mechanism of fuel injection and distribution when fuel and air are injected through coaxial lobe injectors. The main attention of this work is to present the mechanism of fuel mixing of transverse jet injected from various lobe injectors. Comparison of coaxial gets (air and fuel jet) with equivalent simple jet (fuel without air jet) is done to achieve an efficient model for the combustion chamber. In this work, finite-volume is used to simulate and study of fuel injection performance of a transverse hydrogen jet in different lobe injectors. 3-D flow visualizations are done to reveal the mechanism of the fuel penetration and streamline pattern for introduced models. Strength of circulation and fuel mixing efficiency are also investigated in the present work for 2-, 3-, and 4-lobe nozzles. Our outcomes indicate that the mixing performance of coaxial air and fuel jet injected through the 3-lobe nozzle is about 25% better than other nozzle types. Our findings confirm that injection of air jet through the core of the lobe nozzle increases fuel mixing up to 200% at the combustion chamber.     

低排放燃烧室燃料空气预混均匀性研究

为了解决燃料与空气均匀预混的问题,以气态燃料-低排放塔式同轴分级燃烧室为研究对象,采用数值模拟与实验设计数理统计方法相结合,研究了主燃级叶片角、叶片数、燃料速度和单面孔数对燃料和空气预混特性的影响,筛选出对燃料空气预混均匀性影响的显著项,并拟合得出均匀性的预测公式。结果表明：单面孔数及其平方项对预混均匀性影响最大;燃料速度与叶片角、燃料速度与单面孔数的交互效应其次;叶片数、叶片角、燃料速度及其平方项和交互项对均匀性的影响最小。     

缸内直喷周向分层燃烧系统火花塞附近油束发展历程的试验研究

采用高速摄影技术研究了缸内直喷周向分层（简称DICSC）燃烧系统火花塞附近两根油历史潮流的发展历程。研究结果表明,喷雾混合过程中燃油碰壁、反弹现象非常明显,大多数燃油的雾化与蒸发产生于油束碰壁以后。靠近壁面处燃油浓度最大,向燃烧室中心方向浓度逐渐降低,沿周向、顺涡流方向形成了明显的由浓到稀的分层。因而,为了保证较好的着火稳定性,在DICSC燃烧系统中火花塞靠近壁面布置并处于油束下游一定角度比较合适,此外有浓度合适、易于点燃的混合气以便火焰能够顺利扩展。另外,还研究了不同涡流比和油束夹角下的油束发展历程。     

模型燃烧室燃烧自激振荡与音频特征的实验研究

以甲烷为燃料,在以GE燃机6B喷嘴为基础的1/3模型燃烧室中,研究了燃烧室空气流量和当量比的变化对燃烧自激振荡的压力波动的影响,以及燃烧发出的音频信号的特征。实验结果显示：在3组不同的入口空气流量工况下,随着当量比的增加,燃烧室的稳定——自激振荡——稳定工作的变化趋势保持一致;在不同的流量下,当量比=0.61的工况产生了最强烈的自激振荡,同时振荡的压力波动幅值和频率随燃烧室入口空气流量的增加而增大;通过FFT（快速傅里叶变换）计算发现,在有明显自激振荡的工况中,动态压力与音频信号的幅值均大幅超过稳定燃烧的工况,同时音频信号的一个特征频率与动态压力信号的特征频率重合。     

一种基于稀扩散燃烧的BUMP燃烧室及其对柴油机碳烟和NOx排放影响的实验研究

在壁面布置限流沿 (BUMP)后 ,撞壁射流从壁面被剥离 ,形成二次空间射流 ,可大大加快空气与流体的混合速率。基于此 ,设计了带有 BUMP的燃烧室 ,采用了可灵活控制喷油规律的 FIRCRI电控共轨式喷油系统进行了发动机实验。实验结果表明 :BU MP燃烧系统能显著降低 NOx 和碳烟排放 ,在平均有效压力为 0 .6 6 MPa(原机 5 0 %负荷 )时 ,烟度只有 0 .1BSU,NOx 为 42 0× 10 - 6;由于在缸内能够形成较均匀的混合气 ,缸内平均过量空气系数在 1.3～ 2 .0的范围内时 ,烟度一直保持在 0 .3BSU以下。实验还发现 BUMP的位置以及喷油定时对排放有重要影响。BUMP燃烧系统在降低 NOx 和碳烟排放方面显示了极大的潜力。     

柴油机新型双卷流燃烧系统混合与燃烧机理研究

本提供了新型ＤＳＣＳ的结构和原理，其核心是在ＤＳ燃烧室内，燃油射流触脊，分裂并呈双卷流进行了混合与燃烧。在自制的燃油喷雾模型试验装置上，采用油－油喷射技术，对燃烧室模型内的燃油射流流动过程进行高速摄影，并对多种试验方案的拍照结果进行了分析。模型试验表明，ＤＳＣＳ中燃油射流流程可细分为４个阶段，采用了新机理，新理论进行了混合与燃烧。     

直喷式增压柴油机燃烧过程可视化研究

介绍采用高速摄影技术研究直喷式增压柴油机的燃烧过程，研究工作在单缺柴油机上进行。研究结果表明，进气增压改善了上柴油机燃烧过程；促进了燃油和空气的混合，增加了燃油束向燃烧室中心的扩展区域，壁面附近燃油堆积量减小；缩短了着火延迟期，增加了扩散燃烧的比例，火焰扩展速度降低；改善了燃烧室内的燃烧条件，抑制了燃烧火焰向活塞顶部外溢。     

Thermal performance of a meso-scale liquid-fuel combustor

Combustion in small scale devices poses significant challenges due to the quenching of reactions from wall heat losses as well as the significantly reduced time available for mixing and combustion. In the case of liquid fuels there are additional challenges related to atomization, vaporization and mixing with the oxidant in the very short time-scale liquid-fuel combustor. The liquid fuel employed here is methanol with air as the oxidizer. The combustor was designed based on the heat recirculating concept wherein the incoming reactants are preheated by the combustion products through heat exchange occurring via combustor walls. The combustor was fabricated from Zirconium phosphate, a ceramic with very low thermal conductivity (0.8 W m⁻¹ K⁻¹). The combustor had rectangular shaped double spiral geometry with combustion chamber in the center of the spiral formed by inlet and exhaust channels. Methanol and air were introduced immediately upstream at inlet of the combustor. The preheated walls of the inlet channel also act as a pre-vaporizer for liquid fuel which vaporizes the liquid fuel and then mixes with air prior to the fuel–air mixture reaching the combustion chamber. Rapid pre-vaporization of the liquid fuel by the hot narrow channel walls eliminated the necessity for a fuel atomizer. Self-sustained combustion of methanol–air was achieved in a chamber volume as small as 32.6 mm³. The results showed stable combustion under fuel-rich conditions. High reactant preheat temperatures (675 K–825 K) were obtained; however, the product temperatures measured at the exhaust were on the lower side (475 K–615 K). The estimated combustor heat load was in the range 50 W–280 W and maximum power density of about 8.5 GW/m³. This is very high when compared to macro-scale combustors. Overall energy efficiency of the combustor was estimated to be in the range of 12–20%. This suggests further scope of improvements in fuel–air mixing and mixture preparation.     

Three-dimensional fuel–air mixing phenomena in a side-dump combustor: A numerical study

Three-dimensional fuel–air mixing phenomena in a side-dump combustor with fuel injectors arranged in dual curved side-inlet ducts are numerically investigated in the present paper. The model adopts a complete computational domain, including side-inlet ducts and combustion chamber, for numerical calculations. Three cases with different locations of fuel injector are analyzed to investigate the effects of fuel injecting positions on the flow structures and mixing phenomena in side-inlet ducts as well as in combustion chamber. The results show that the interaction of curvature effects of side-inlet ducts and the fuel injection flow significantly change the vortex motion in the curved side-inlet ducts. The axial recirculation and fuel distributions in the combustion chamber are also found to be influenced substantially by the fuel injection, which indicates the precise control of the fuel injection is very important for getting good fuel distributions, and in turn to achieve good combustion performance.     

高速直喷柴油机燃烧室形状与喷孔结构匹配规律的三维仿真研究

对某高速直喷柴油机的燃烧过程进行了多维仿真计算,研究了燃烧室形状和喷孔结构参数之间的匹配规律.通过变参数研究确定了燃烧室形状和喷孔结构参数之间的匹配规律.为了定量描述燃烧过程中燃油雾化、液体蒸发、油气混合的特性,建立了缸内平均湍流混合速率、燃油蒸气质量分数方差的中间特征参数,同时详细分析了不同当量比油气混合气在燃烧过程中的贡献率.从燃烧的宏观和微观角度综合分析了柴油机燃烧室形状与喷孔结构间的耦合作用机制.结果表明,对于所研究的机型,0.64口径比燃烧室匹配10孔喷油器的方案最优:预混过程好,燃烧速度快,后期扩散燃烧阶段过稀和过浓混合气参与燃烧的比例较小且预混与扩散燃烧放热情况差别小,放热情况更均匀.     

"Bump燃烧室"内新概念稀扩散燃烧混合气形成机理的研究

基于自行研制的实验装置,用片状激光诱导荧光法(PLIF)对普通商用柴油喷雾的撞壁混合过程进行了实验研究,并用CFD数值分析软件对其进行了模拟计算,二者结果基本吻合．平板和实际燃烧室的实验及计算结果均表明,撞壁射流在遇到限流沿(Bump)后会剥离壁面,形成二次空间射流,扩大撞壁射流与空气的空间混合体积及混合速率,出现与周围空气迅速混合的“闪混”现象,减少壁面燃油堆积量．计算结果还表明,Bump的存在改变了缸内气流运动的流场结构,Bump附近旋向相反的“双涡结构”极大地增强了二次空间射流对周围空气的卷吸,促进了燃油与空气的混合,是Bump燃烧室内稀混合气形成及稀扩散燃烧的关键所在．     

BUMP燃烧室的稀扩散燃烧机理

开发了BUMP燃烧室并进行了对比实验,发现BUMP燃烧室中可以形成稀的扩散燃烧氛围,使NOx和碳烟排放同时降低．喷射定时3°CA ATDC时,烟度排放降低了约70％,NOx排放与对比燃烧室相当．CFD模拟研究表明,不同的喷射定时下,燃油到达燃烧室壁面时的混合和燃烧状态不同,只有油束在滞燃期内到达燃烧室壁面,由限流沿(BUMP环)扰动形成的二次空间射流才能充分形成,稀扩散燃烧才能明显发生．     

Mixing and stabilization study of a partially premixed swirling flame using laser induced fluorescence

A laboratory-scale swirling burner, presenting many similarities with gas turbines combustors, has been studied experimentally using planar laser induced fluorescence (PLIF) on OH radical and acetone vapor in order to characterize the flame stabilization process. These diagnostics show that the stabilization point rotates in the combustion chamber and that air and fuel mixing is not complete at the end of the mixing tube. Fuel mass fraction decays exponentially along the mixing tube axis and transverse profiles show a gaussian shape. However, radial pressure gradients tend to trap the fuel in the core of the vortex that propagates axially in the mixing tube. As the mixing tube vortex enters the combustion chamber, vortex breakdown occurs through a precessing vortex core (PVC). The axially propagating vortex shows a helicoidal trajectory in the combustion chamber which trace is observed with transverse acetone PLIF. As a consequence, the stabilizing point of the flame in the combustion chamber rotates with the PVC structure. This phenomenon has been observed in the present study with a high speed camera recording spontaneous emission of the flame. The stabilization point rotation frequency tends to increase with mass flow rates. It was also shown that the coupling between the PVC and the flame stabilization occurs via mixing, explaining one possible coupling mechanism between acoustic waves in the flow and the reaction rate. This path may also be envisaged for flashback, an issue that will be more completely treated in a near future.     

大加速度场中层流扩散火焰流场的数值计算

通过对大加速度场中层流燃烧室流场的数值计算,建立了大加速度场中二维层流燃烧的数学模型,对控制方程组进行离散,采用SIMPLE算法和交错网格设计并调试程序。在调试成功的程序上对甲烷和空气在大加速度场中的扩散燃烧过程进行了数值模拟。计算结果表明,沿燃烧室轴线方向的均匀大加速度场会对扩散火焰的速度场和温度场等产生明显影响。一方面使得燃料与空气的扩散混合过程得到强化,扩散火焰的形状变短变粗,火焰面温度升高．因而能够提高其燃烧速度;另一方面,由于浮力作用驱动高温气流的流动方向与燃料射流的方向相反,将形成一种不稳定的流场结构,并同时诱发燃烧过程的不稳定。     

The presence of downstream ramp on fuel mixing of the multi micro jets at supersonic cross flow

Development of the fuel injection system in combustion chamber is greatly important for the overall thrust efficiency of the high-speed vehicles. Current article developed a three-dimensional model to discover the reality of downstream ramp on fuel mixing of the multi-jet at Ma>1. FVM is hired to scrutinize the impact of injector types (3-lobe, circular and rectangular shape) on the mixing productivity of downstream ramp in combustion chamber. Besides, the effects of ramp angle on fuel mixing are also analysed. Fuel mixing mechanisms in the selected models are investigated by comparing the Ma contour and mixing zone. Comparisons of the circulation strength downstream of these models confirm that the 3-lobe nozzles is more efficient than other styles. Our comparison indicates that overall mixing productivity of the circular jet is more than other cases.     

对置活塞发动机侧置燃烧室性能仿真研究

为解决使用中心浅坑燃烧室的对置活塞发动机燃油湿壁、挤流强度低、燃烧室中心混合气过浓等问题,提出对置活塞发动机侧置燃烧室方案,对侧置ω燃烧室和侧置侧卷流燃烧室性能进行研究.使用侧置燃烧室时气口开闭相位的改变会导致发动机指示功率降低,采用GT-Power建立发动机性能仿真模型,通过改变气口参数解决了由于换气过程差异导致的侧...