利用PLIEF技术对重型柴油机类似环境条件下着火时刻柴油喷雾结构和浓度场的定量研究

利用复合激光诱导荧光技术在定容燃烧弹内定量研究了环境温度、环境密度、氧体积分数等对重型柴油机相似环境条件下着火时刻柴油喷雾结构和浓度场的影响.实验中,环境密度为20～ 60 kg/m3,氧体积分数为l 5％～21％.研究发现,重型柴油机相似环境条件下着火时刻柴油喷雾液核区同时存在当量比相对较高的气相喷雾;喷雾充分发展后...     

复合激光诱导荧光定量标定技术及其对喷雾特性研究的应用Ⅰ:燃油喷雾当量比定量标定方法

应用复合激光诱导荧光技术建立了定容燃烧弹中荧光强度和喷雾浓度间关系的定量标定方法,获得柴油喷雾气相、液相浓度量化数值,并针对影响定量标定的各种环境因素开展了深入的量化研究。试验中分析了荧光强度和气相喷雾浓度间的系数(Kvapor)随环境条件改变时的变化情况并发现:系数Kvapor随环境压力升高而降低;环境气体成分的变化对系数Kvapor并没有明显影响;环境温度升高使得系数Kvapor呈现先上升后下降的趋势,600K左右是拐点位置,600K以前随温度升高而升高,600K以后随温度升高而快速下降。最终,根据试验结果建立了系数Kvapor随环境温度和环境压力变化的三维Map图,并应用其获得喷雾气相当量比浓度数值和液相浓度数值的定量结果。     

超高喷油压力下柴油喷雾撞壁特性的定量研究

在一个定容弹里,利用复合激光诱导荧光技术(PLIEF)定量研究了柴油喷雾撞击平板后的燃油分布.试验在180、220和260 MPa3种超高喷油压力下进行的.研究发现,在气/液相喷雾同时撞壁的条件下气相喷雾瞬态最大当量比φ_(max)出现在撞壁点附近,气相喷雾瞬态最低温度T_(min)出现在气相喷雾瞬态最大当量比位置,并与其发展规律截然相反.随着喷油压力的增加,喷雾与环境气体的混合率明显提高,具体表现为:撞壁后气相喷雾φ_(max)变化不大,但液相燃油的质量分数下降,而当量比φ≤2区间的气相燃油质量分数增加,φ2区间的气相燃油质量分数下降.     

利用PLIEF技术对重型柴油机类似环境条件下柴油喷雾特性和浓度场的定量研究

利用复合激光诱导荧光技术在定容弹内定量研究了环境温度、环境密度、氧浓度等对重型柴油机类似环境条件下柴油喷雾特性和浓度场的影响。试验中,环境密度为20～100kg/m3,氧浓度为15%～21%,喷油压力为100～220MPa。研究发现,提高环境密度,最大液核长度显著缩短;减小喷孔直径,液核最大长度呈线性下降。降低环境温度或提高喷油压力可以弥补减小喷孔直径或提高环境密度对贯穿距离的影响。在增加充分发展期气相喷雾稀混区燃油比例方面,减小喷孔直径、降低环境温度、提高环境密度和提高喷油压力具有相互替代性。     

应用激光诱导荧光法研究超高压喷雾气液相浓度场分布特性

应用复合激光诱导荧光技术在光学发动机上测量了燃油喷雾气液两相荧光图像，提出分析浓度场分布的无量纲参数，最终获得喷雾气液相浓度场相对分布。实验采用电机倒拖的光学发动机，燃烧室采用ω形BUMP燃烧室，应用自行设计的脉冲压力放大供油系统，实现了最高喷油压力达240MPa的超高压喷射。通过研究发现，随着喷油压力提高可有效加速喷雾气相生成、促进喷雾气相的均匀分布。这种效果在有较强挤流作用和存在BUMP燃烧室限流沿剥离作用下更为明显，此时喷雾气相相对浓度随着喷油压力从160MPa提高到240MPa而下降62．5％。     

BUMP燃烧室内柴油喷雾气液相缸内浓度场测量激光诱导荧光法的实现和研究

本文应用复合激光诱导荧光（Planar Laser Induced Exciplex Fluorescence）测试技术,实现了对BUMP燃烧室内柴油喷雾的气液相浓度分布同时进行测量的光学测试系统,并研究了改变BUMP燃烧室形状和二次撞壁距离对喷雾气液相浓度场分布的影响情况。研究发现,BUMP燃烧室形状对喷雾缸内分布有明显作用,合适的BUMP高度能够剥离撞壁喷雾,形成二次射流,加速喷雾在燃烧室内与空气的混合,研究中缩口角度14°,BUMP高度1.5mm的BUMP燃烧室具有研究中最理想的喷雾气液相缸内分布。     

DME闪急沸腾喷雾特性的试验与数值模拟研究

在压力定容室内,利用数字粒子图像速度场仪(DPIV)对二甲醚(DME)闪急沸腾喷雾特性,以及DME和柴油的常规喷雾特性开展了试验研究;建立了适用于DME闪急沸腾喷雾的宏观现象学模型,并将该模型与KIVA程序相耦合,藉此对DME闪急沸腾喷雾特性进行了数值模拟.研究结果表明:与柴油常规喷雾相比,DME闪急沸腾喷雾贯穿距较短,但喷雾锥角较大;喷雾初始段的计算值与试验测量值吻合较好,但喷雾后期的吻合程度稍差.计算研究表明:DME闪急沸腾喷雾体前端两侧存在着明显的涡环结构,喷雾场中DME的气相浓度大幅度高于柴油喷雾的气相浓度,且其索特平均直径(SMD)比柴油小得多.     

两次喷射柴油喷雾特性的定量研究

利用复合激光诱导荧光技术,在定容燃烧弹内,对单次喷射和两次喷射时柴油喷雾发展过程及喷雾特性进行研究,结果表明,喷雾发展伴随液滴蒸发和气体卷吸的相互竞争.喷雾发展初期气液相同时形成,液滴蒸发速率较小,气相大部分位于Φ<2区间.喷雾发展中期蒸发速率逐渐升高,喷雾内部形成Φ>2的过浓区.喷雾充分发展后气体卷吸占主导,过浓区减小.两次喷射时,停喷间隙可促进油气混合,降低过浓混合气的质量分数,从而改善碳烟排放;另一方面,两次喷射影响油气空间分布,减小喷雾前锋油气堆积,使过浓混合气与稀混合气燃烧区相分离,有效抑制碳烟的生成.     

撞壁距离对柴油喷雾特性的影响

利用复合激光诱导荧光(PLIEF)技术,通过高温高压定容燃烧弹研究了撞壁距离对柴油喷雾撞击平板后的燃油分布影响.试验中,撞壁距离从12.5 mm变化到32.5 mm.结果表明:撞壁距离对燃油分布有重要影响,随着撞壁距离的增加,液相燃油质量分数增加,过浓区间(φ2)的气相燃油质量分数减小,较浓区间(1φ≤2)的气相燃油质量分数增加到一定数量并保持变化不大,稀混合气区间(0φ≤1)的气相燃油质量分数逐渐增加;瞬态最大当量比(φmax)降低;瞬态最低温度(Tmin)发展趋势与φmax相反;气/液相喷雾壁面射流半径和高度大幅减小,甚至不与壁面相撞.     

撞壁对柴油喷雾燃油分布影响的试验和计算

利用复合激光诱导荧光(PLIEF)技术,在一个定容弹里定量研究了柴油喷雾撞击平板后的燃油分布,重点研究了撞壁距离对气相燃油分布的影响.结果表明:撞壁对燃油分布有重要影响,随着撞壁距离的增加,气/液相喷雾撞壁时刻延迟甚至不与壁面接触,当量比φ2区间的气相燃油质量分数减小,1φ≤2区间的气相燃油质量分数增加到一定数量并保持变化不大,0φ≤1区间的气相燃油质量分数逐渐增加.数值模拟计算的结果发现,存在一个基于氮氧化物(NO)和碳烟(soot)排放折中的最优撞壁距离与喷孔直径之比(L/D)范围使得液相燃油不与壁面接触,φ2区间和0φ≤1区间的气相燃油质量分数较小,1φ≤2区间的气相燃油质量分数较多,NO和soot排放都较小.根据计算结果拟合了基于NO和soot排放折中的最优撞壁距离范围的经验公式,可以很好地预测不同工况下的最优撞壁距离范围.     

Investigation of heat and mass transfer between the two phases of an evaporating droplet stream using laser-induced fluorescence techniques: Comparison with modeling

Heat and mass exchanges between the two phases of a spray is a key point for the understanding of physical phenomena occurring during spray evaporation in a combustion chamber. Development and validation of physical models and computational tools dealing with spray evaporation requires experimental databases on both liquid and gas phases. This paper reports an experimental study of evaporating acetone droplets streaming linearly at moderate ambient temperatures up to 75 °C. Two-color laser-induced fluorescence is used to characterize the temporal evolution of droplet mean temperature. Simultaneously, fuel vapor distribution in the gas phase surrounding the droplet stream is investigated using acetone planar laser-induced fluorescence.Temperature measurements are compared to simplified heat and mass transfer model taking into account variable physical properties, droplet-to-droplet interactions and internal fluid circulation within the droplets. The droplet surface temperature, calculated with the model, is used to initiate the numerical simulation of fuel vapor diffusion and transport in the gas phase, assuming thermodynamic equilibrium at the droplet surface. Influence of droplet diameter and droplet spacing on the fuel vapor concentration field is investigated and numerical results are compared with experiments.     

燃油温度对喷雾特性的影响研究

以KIVA-3V为基础,研究了在定容室喷雾条件下,燃油温度对喷雾气液相贯穿距、气相总体积及气相混合气燃空当量比分布的影响。研究结果表明:随着燃油温度的升高,喷雾的液相及气相贯穿距缩短,蒸发喷雾在径向上的扩展明显增强,喷雾蒸发的气相体积几乎呈线性增加;在燃油温度为293K时,喷雾中气相混合气燃空当量比小于1的油气质量占所蒸发总油气质量的90%以上,而燃空当量比大于2的油气质量近乎为零;但当燃油温度达530K时,喷雾中气相混合气燃空当量比大于2的油气质量约占所蒸发油气总质量的70%。     

柴油机喷雾油束内温度与浓度分布的研究

柴油机缸内局部燃油蒸气的温度与浓度是影响柴油机着火与燃烧的重要因素，因此研究喷雾油束内燃油温度与浓度分布具有一定的实际意义。作在Ｅ１５０柴油机上，采用激光双曝光全息干涉技术，假定喷雾油束为轴对称圆锥形，将燃油蒸气作为位相物体处理，测取了喷雾油束的干涉条纹，采用阿贝尔变换对干涉条纹进行反演，导出了油束内轴向与径向位置的折射率，并由此计算出喷雾油束内燃油温度与浓度的分布。     

High-pressure vaporization modeling of multi-component petroleum–biofuel mixtures under engine conditions

Numerical simulation of the vaporization of multi-component liquid fuels under high-pressure conditions is conducted in this study. A high-pressure drop vaporization model is developed by considering the high-pressure phase equilibrium which equates the fugacity of each component in both liquid and vapor phases. Peng–Robinson equation of state is used for the calculation of fugacity. To model the vaporization of diesel fuel under high-pressure conditions, continuous thermodynamics based on a gamma distribution is coupled with phase equilibrium by correlating the parameters of the equation of state with the molecular weights of the continuous components. The high-pressure vaporization model is validated using the experimental data of n-heptane drops under different ambient pressures and temperatures. Good levels of agreement are obtained in drop size history. Predicted results of the vaporization of diesel fuel drops show that increasing ambient pressure leads to a shorter drop lifetime under high temperature conditions (e.g., 900 K). On the other hand, at a slightly lower temperature of 700 K, the drop lifetime increases as the ambient pressure increases. It is found that the net affects of high ambient pressure on drop vaporization are determined by two competing factors, namely, reduced mass transfer number and reduced enthalpy of vaporization. The model was further applied to biodiesel and its blends with diesel fuel. The fuel blend is modeled based on a method that continuous thermodynamics is used to model diesel fuel and biodiesel is modeled as a mixture of its five representative components. Results of single drop vaporization history show that drop lifetime increases as the volume fraction of biodiesel in the fuel blend increases. This phenomenon reveals the low vaporization rate of biodiesel that has a higher critical temperature than diesel fuel. It is also observed that the volume fraction of biodiesel in the fuel blend increases during vaporization and its vapor concentrates near the tip of the liquid spray while diesel fuel vapor is around the entire liquid spray.     

高温条件下柴油机喷雾粒度的测量

为了了解柴油机燃烧室中燃油与空气的混合及后续燃烧过程，准确地描述燃油雾化和油洋蒸发过程是至关重要的。运用激光衍射法测量注体喷雾粒度具有对喷雾无干扰，设备简单数处理迅速等优点，但这种方法对加热环境中的蒸发液雾进行测量进，由于光路上存在的温度及浓度梯度，激光被折射而偏转，结果受到严重影响，以往对柴油机喷雾的测量大都在常温不蒸发条件下进行的，而本则是通过对粒子激光衍射测量原理的深入分析，对基于激光衍射     

空心喷雾油滴碰撞热多孔介质的数值研究

为加深对多孔介质发动机中均匀混合气形成的了解,用改进的KIVA-3V详细模拟了空心喷雾油滴碰撞热多孔介质的过程。在KIVA-3V中增加了油滴碰撞热多孔介质壁面的碰撞模型、传热模型及空心喷雾的线性不稳定性液膜破碎(LISA)模型。油滴与热壁的碰撞模型和传热模型经检验证明了其合理性。在简化多孔介质结构的基础上,在不同的环境压力及喷雾锥角下,模拟了空心喷雾与热多孔介质的相互作用。计算结果表明:油雾在碰撞到热多孔介质后,发生分裂的油束和多孔介质区域的高温,促使油滴实现快速蒸发并为油蒸汽与空气充分混合创造了前提。不同的空间压力及喷雾锥角直接影响到油滴在多孔介质中的分布。     

The effect of ambient pressure on the evaporation of a single droplet and a spray

The effect of ambient pressure on the evaporation of a droplet and a spray of n-heptane was investigated using a model for evaporation at high pressure. This model considered phase equilibrium using the fugacities of the liquid and gas phases for the behavior of a gas being real, and its importance in the calculation of the evaporation of a droplet or spray at high pressures was demonstrated. For the evaporation of a single droplet, the fact that the droplet's lifetime increased with pressure at a low ambient temperature, but decreased at high temperatures, was explained with pressure and the droplet's temperature determining phase equilibrium. In this study, it was also found that the evaporation of a spray can be explained in terms of multiplex dependencies of the atomization and evaporation of a single droplet. The evaporation of a spray was enhanced by increasing the ambient pressure and this effect was more dominant at higher ambient temperatures.     

Numerical simulation of fuel sprays at high ambient pressure: the influence of real gas effects and gas solubility on droplet vaporisation

This paper deals with the numerical simulation of the vaporisation of an unsteady fuel spray at high ambient temperature and pressure solving the appropriate conservation equations. The extended droplet vaporisation model accounts for the effects of non-ideal droplet evaporation and gas solubility including the diffusion of heat and species within fuel droplets. To account for high-temperature and high-pressure conditions, the fuel properties and the phase boundary conditions are calculated by an equation of state and the liquid/vapour equilibrium is estimated from fugacities. Calculations for an unsteady diesel-like spray were performed for a gas temperature of 800 K and a pressure of 5 MPa and compared to experimental results for droplet velocities and diameter distribution. The spray model is based on an Eulerian/Lagrangian approach. The comparison shows that the differences between the various spray models are pronounced for single droplets. For droplet sprays the droplet diameter distribution is more influenced by secondary break-up and droplet coagulation.