Effect of Nozzle Inclination Angle on Fuel-Air Mixing and Combustion in a Heavy Fuel Engine

Heavy-fuel engines are widely used in UAVs(Unmanned Autonomous Vehicles)because of their reliability and high-power density.In this study,a combustion model for an in-cylinder direct injection engine has been imple-mented using the AVL FIRE software.The effects of the angle of nozzle inclination on fuel evaporation,mixture distribution,and combustion in the engine cylinder have been systematically studied at 5500 r/min and consider-ing full load cruise conditions.According to the results,as the angle of nozzle inclination increases,the maximum combustion explosion pressure in the cylinderfirst increases and then it decreases.When the angle of nozzle incli-nation is less than 45°,the quality of the mixture in the cylinder and the combustion performance can be improved by increasing the angle.When the angle of nozzle inclination is greater than 45°,however,the mixture unevenness increases slightly with the angle,leading to a deterioration of the combustion performances.When the angle of nozzle inclination is between 35°and 55°,the overall combustion performance of the engine is rela-tively good.When the angle of nozzle inclination is 45°,the combustion chamber’s geometry and the cylinder’s airflow are well matched with the fuel spray,and the mixture quality is the best.Compared with 25°,the peak heat release rate increases by 20%,and the maximum combustion burst pressure increases by 5.5%.

Catalytic performance for methane combustion of supported Mn-Ce mixed oxides

A series of supported Mn-Ce mixed oxide catalysts were prepared by the impregnation method and used for the oxidation of methane. The catalysts were characterized by N2 adsorption （BET）, X-ray diffraction （XRD）, laser Raman spectrum （LRS）, and temperature programmed reduction （TPR） techniques. The XRD and LRS results confirmed the high dispersion of active components or formation of solid solution between manganese and cerium oxides in the bulk and on the surface of mixed oxide catalysts. The reducibility was remarkably promoted by the stronger synergistic interaction between the two oxides from H2-TPR measurements. As expected, all the experimental mixed oxide catalysts showed excellent activity for methane combustion at low temperature. Especially, for the catalyst with Mn-Ce ratio 3：7, methane conversion reached 92% at a temperature as low as 470 ℃.

Experimental Investigation of the Effect of Mixed Additives on Homogeneous Charge Compression Ignition Combustion

The experimental investigation of homogeneous charge compression ignition (HCCI) process is carried out on a 4-cylinder diesel engine. One of the cylinders is modified for HCCI combustion with mixed additives. The influence of mixed additives on the HCCI combustion process is investigated. The experimental results indicate that the mixed additives are better than the single additives for HCCI fuel, causing ignition and heat release to be advanced and the peak of heat release rate to increase under the condition of different engine speeds and steady HCCI combustion. Moreover, with the increase in engine speed, the influence of mixed additives on HCCI combustion is more obvious. In addition, the mixed additives are beneficial to improve HCCI engine misfire at a high engine speed and make the engine operate stable.

Experimental Study of MHD-Assisted Mixing and Combustion Under Low Pressure Conditions

In order to reveal the mechanism of MHD-assisted mixing, and analyse the major parameters which influence the effect of MHD-assisted mixing, experiments of MHD-assisted mixing are carried out with a non-premixed butane-air combustion system. The evolvement of the discharge section and the effect of MHD-assisted mixing on combustion are investigated by changing the magnetic flux density and airflow velocity. The results show that the discharge area not only bends but also rotates around the centered wire electrode, which are mainly caused by the Lorentz force. Moreover, the highest curvature occurs near the centered wire electrode.The discharge localizes near the surface of the wire electrode and annular electrode when there is no ponderomotive force. However, if the ponderomotive force is applied, the discharge happens between these two electrodes and it gradually shrinks with time. The discharge area cannot localize near the annular electrode, which is due to the increase of energy loss in the airflow.When the airflow velocity exceeds a certain value, the discharge section becomes unstable because the injected energy cannot maintain the discharge. The rotation motion of the discharge section could enlarge the contact surface between butane and air, and is therefore beneficial for mixing and combustion. Magnetic flux density and airflow velocity are critical parameters for MHD-assisted mixing.

THE COMBUSTIBILITY OF CHINESE FIR AND MACCLURE MICHELIA MIXED FOREST

Based on the theory of forest burning link, the combustibility of the 6-year-old Chinese fir (Cunninghamia lanceolata) and macclure michelia (Michelia macclurei) mixed forest was determined in Youxi County, Fujian Province from 1988 to 1989. The results show that the daily mean moisture in the forest, moisture content of litter and the water reserves of the stand in mixed forest are 3%, 7.6% and 46.8% higher than that in pure stand respectively, the inflammables quantity and energy ratios of the stand biomass and total potential energy in mixed stand are 8.5% and 3.69% lower than that in pure stand respectively. Mixed forest can decrease the combustibility of stand.

Effect of kerosene injection states on mixing and combustion characteristics in a cavity-based supersonic combustor

It has been found that the static pressure distribution along the axial direction of liquid kerosene is lower than that of the gaseous kerosene under the same flow condition and overall equivalent ratio from previous studies.To further investigate this phenomenon,a compressible two-phase parallel simulation method is utilized to analyze the mixing and combustion characteristics of gaseous and liquid kerosene jets in a cavity-based supersonic combustor.The numerical results are consistent with the experiments and demonstrate that gaseous injection leads to a cavity shear layer that dives deeper into the cavity,forming two recirculation zones in the front and rear of the cavity.In contrast,the cavity shear layer is closer to the mainstream during liquid injection,and only a large recirculation zone is formed in the rear of the cavity.As a result of the cavity shear layer and the recirculating flow,the fuel vapor of gaseous injection accumulates in the front of the cavity,while for the liquid injection,the fuel vapor disperses in the cavity,cavity shear layer,and the region above,and the rear of the cavity has a higher fuel vapor concentration than the front.This unique fuel distribution causes the combustion area to be concentrated in the cavity during the gaseous injection but dispersed inside and downstream of the cavity during the liquid injection.As a result,forming a thermal throat under the same conditions is more challenging during liquid injection,and the generated static pressure distribution is lower than that during the gaseous injection.

Study on the influences of interaction behaviors between multiple combustion-gas jets on expansion characteristics of Taylor cavities

The purpose of this study is to investigate means of controlling the interior ballistic stability of a bulk-loaded propellant gun（BLPG）.Experiments on the interaction of twin combustion gas jets and liquid medium in a cylindrical stepped-wall combustion chamber are conducted in detail to obtain time series processes of jet expansion,and a numerical simulation under the same working conditions is also conducted to verify the reliability of the numerical method by comparing numerical results and experimental results.From this,numerical simulations on mutual interference and expansion characteristics of multiple combustion gas jets（four,six,and eight jets） in liquid medium are carried out,and the distribution characteristic of pressure,velocity,temperature,and evolutionary processes of Taylor cavities and streamlines of jet flow Held are obtained in detail.The results of numerical simulations show that when different numbers of combustion gas jets expand in liquid medium,there are two different types of vortices in the jet flow field,including corner vortices of liquid phase near the step and backflow vortices of gas phase within Taylor cavities.Because of these two types of vortices,the radial expansion characteristic of the jets is increased,while changing numbers of combustion gas jets can restrain Kelvin-Helmholtz instability to a certain degree in jet expansion processes,which can at last realize the goal of controlling the interior ballistic stability of a BLPG.The optimum method for both suppressing Kelvin-Helmholtz instability and promoting radial expansion of Taylor cavities can be determined by analyzing the change of characteristic parameters in a jet flow field.

EGR技术对生物柴油混合燃料发动机性能的影响研究

为缓解柴油掺烧生物柴油导致的NO_(x)排放过高问题,将4190ZLC船用中速柴油机作为试验台架,通过AVL_FIRE软件建立燃烧室模型,并验证该模型准确性。设置生物柴油掺混比0~40%等4组变量,EGR率0~12.5%等4组变量,进行柴油机燃烧、性能和排放分析。结果表明,掺烧适量生物柴油能够降低柴油机缸内温度,降低Soot排放,但同时会导致NO_(x)排放明显升高;EGR的引入能够实现低温燃烧,显著降低NO_(x)排放,但EGR率过高会增加Soot排放。生物柴油掺混比B40、EGR率12.5%组合NO排放比原机降低47.7%,Soot排放质量分数比原机降低98.13%。本文结果将为柴油掺混生物柴油燃烧并结合EGR技术提供一定的研究方向。

H_(2)与氨混燃增强火焰燃烧特性模拟研究

氢和氨作为清洁能源受到广泛关注,为深入探究氢-氨混燃的燃烧特性和影响因素,本文借助Chemkin仿真平台建立相关反应模型,以氢-氨混合气体为燃料,空气作为助燃剂,采用Otomo等人提出的一种氨氧化机理对其燃烧过程进行模拟计算,并模拟研究了混合气体的点火延迟时间、层流燃烧速度、绝热燃烧温度、NO排放等燃烧特性随当量比、初始压力以及燃料中H_(2)比例的具体变化规律,对不同工况下的层流火焰结构、H和OH自由基的产率(rate of production,ROP)、NO生成的敏感度进行了化学动力学分析。结果表明:纯氨气体的点火延迟时间长、层流燃烧速度慢,掺氢后燃烧特性均有所改善,且提高了火焰的绝热燃烧温度,但掺氢比例越大,NO排放越多。NO摩尔分数随当量比变化的趋势先增后减,在当量比为0.8左右达到峰值。综合考虑氢-氨混燃的一系列燃烧特性以及掺氢、加压的成本和收益情况,推荐H_(2)占比15%、当量比φ=1.1、压力P=0.2 MPa为氢-氨混合燃烧的最优条件。

氧化剂燃气来流下TAGN富燃料掺混燃烧特性

在新型氧/燃分离式组合固体发动机中,氧化剂燃气来流工况对富燃料掺混燃烧特性具有重要影响。为揭示氧化剂来流下富燃料掺混燃烧特性,基于课题组前期建立的氧化剂/富燃料掺混燃烧反应详细机理,构建了新型氧/燃分离式组合固体发动机二维稳态燃烧模型。通过数值仿真分析,获得了不同来流温度和马赫数下,高氯酸铵(AP)氧化剂燃气对硝酸三氨基胍(TAGN)富燃料掺混燃烧特性的影响。结果表明,随着AP燃气来流的初温升高,沿流动方向的混合效果变强,而沿径向方向的混合效果变差,TAGN富燃料前端传热系数有所提升,燃面平均退移速率出现小幅下降;增大AP燃气来流马赫数,显著强化了AP和TAGN的掺混和传热过程,提高了TAGN燃气和AP燃气之间的反应速率,燃面平均退移速率显著增大。

特征参数对微混喷嘴内燃料与空气混合均匀性影响

由于微混喷嘴尺寸小、数量多且无旋流的结构特点,微混燃烧室结构可能形成新的设计准则。为探究微混喷嘴的混合特性优化方法,提取微混喷嘴内雷诺数、相对预混长度、射流动量比等特征参数,通过大涡模拟模型研究其对混合均匀性的影响规律。结果表明:微混喷嘴内预混距离增加,燃料与空气的掺混空间扩大,混合特性明显提升;在较大的射流动量比下,燃料与空气掺混更加剧烈,混合质量上升;燃料入口流速对于喷嘴混合性能的影响并不明显;雷诺数大于1×10^(5)时,喷嘴内流动达到第二自模化区,混合均匀度不再随雷诺数的变化而改变。通过特征参数对喷嘴的混合均匀度进行拟合,所得公式可在当量比为0.5~1.0、雷诺数大于1×10^(5)及入口空气温度为18~818℃时对混合均匀度进行准确预测。该公式可对微混喷嘴的混合特性进行初步计算,并为其结构设计提供参考经验。

污泥/煤泥混合燃烧过程中N和S污染物迁移规律

为探究污泥/煤泥混合燃烧过程中N、S污染物的排放机理,开展N、S污染物迁移规律研究.基于热重-质谱分析仪获得的污泥/煤泥混合燃烧时气态污染物的基础生成规律,建立污泥/煤泥混合燃烧实验系统,研究不同污泥质量分数、温度下污泥/煤泥混合燃烧的SO_(2)、NO的排放规律,并通过对4个不同阶段燃烧产物的X射线光电子能谱(XPS)检测,研究N、S官能团在燃烧过程中的转化规律.结果表明,污泥质量分数为40%时固硫固氮效果最明显;随污泥质量分数增加,吡啶类氮更多转化为吡咯类氮,使HCN产量增加以及胺类和腈类生成量增加,导致总NO排放量随污泥质量分数增加先增加后减少;有机硫类释放更为完全,燃烧产生的含S污染物增多,灰分中硫酸盐含量同步增长,因此总SO_(2)的释放量随污泥质量分数增加变化较小.

固体火箭超燃冲压发动机点火燃烧过程实验研究

为解决硼基贫氧燃料固体火箭超燃冲压发动机补燃室内硼颗粒超声速点火燃烧难题,设计制造了在超声速燃气射流掺混区域开设观察窗的点火燃烧过程试验样机,开展了含硼贫氧固体燃料的超声速点火试验。试验模拟了26 km,Ma5.9的飞行工况并通过高速摄像获得了点火燃烧过程的火焰形态。试验结果表明:掺混增强装置可以显著改善补燃室内存在的分层流动和一次燃气气固两相分离的现象,为硼颗粒提供良好的点火条件从而提升其附近硼颗粒的点火燃烧性能。通过合理设计掺混增强装置位置,将硼颗粒在一次燃气喷注口附近的高温点火区点燃比在补燃室中段点燃具有更高的燃烧效率,本文设计的燃烧组织结构在试验中实现了硼贫氧固体燃料0.812的燃烧效率。

甲烷掺氢燃料反应动力学特性分析及机理验证

燃气轮机燃用天然气-氢气混合燃料可以大幅降低碳排放。为了研究天然气在不同掺氢比时的燃烧特性,利用Cantera开源程序对其基本反应动力学特性开展研究,计算常压和典型F级燃气轮机运行条件下不同掺氢比时混合燃料的层流火焰速度、点火延迟时间等基本反应动力学参数。分析8种反应机理计算获得的火焰位置、温度场分布、主要燃烧产物(CO_(2)和H_(2)O)、中间燃烧产物(OH基和CO)和微量燃烧产物NO的浓度分布,并与悉尼大学天然气-氢气混合燃料(体积分数50%H_(2)+50%CH_(4))模型燃烧室实验数据进行比较。结果表明,采用DRM22、USC2、Kee以及Miller-Bowman机理计算获得的混合气体燃烧特性与实验结果吻合,耦合加州大学单独的氮氧化物机理后所获得的NO_(x)排放值也具有较高的计算精度。结果可为氢燃料燃气轮机燃烧室性能的后续研究提供理论依据,为氢燃料燃气轮机的安全运行奠定基础。

降速剂及其作用位点对丁羟四组元推进剂燃烧性能的影响规律

为研究降速剂对丁羟四组元推进剂燃烧性能的影响规律,将典型季铵盐和金刚烷衍生物两种高效降速剂引入核壳结构铝基复合颗粒Al@HMX和AP@Al,使其分别作用于HMX颗粒内部和AP颗粒表面,制备了4种含降速剂的铝基复合颗粒(Al/A@HMX,Al/B@HMX,AP@Al/A和AP@Al/B);采用扫描电子显微镜对样品形貌进行了表征;采用高速红外相机拍摄推进剂燃烧过程的火焰红外照片,并对推进剂的爆热、密度、点火延迟时间和燃速进行了测试。结果表明,加入惰性降速剂会导致推进剂爆热降低,而Al@HMX复合颗粒能部分抵消这一现象,使推进剂爆热值增加了338 J/g;降速剂能够抑制AP和HMX的热分解过程,使达到AlO辐射峰值前维持低强度的“平台段”;而引入Al@HMX后,推进剂的点火延迟时间比基础配方减小49.4%;在10~20 MPa范围内两种降速剂均能有效降低推进剂燃速,在此基础上采用Al@HMX可使含季铵盐丁羟四组元推进剂20 MPa下的燃速降低7.1 mm/s(38.4%),压强指数降至0.25;当降速剂作用于AP表面时,含质量分数1%季铵盐的推进剂在20 MPa下燃速可降低5.0 mm/s(27.3%)。

二元超声速混压式进气道亚临界稳定裕度研究

为了研究内收缩比和来流马赫数对二元超声速混压式进气道亚临界稳定裕度的影响规律及失稳机制,采用二维非定常仿真方法研究了内收缩比(ICR)为1.04~1.25的进气道在来流马赫数Ma0为2.4的条件下,以及内收缩比为1.08的进气道在来流马赫数为2.2~2.8条件下,其由稳态向失稳状态转变的过程。研究结果表明:(1)当Ma0=2.4时,在1.04≤ICR≤1.12内,随着ICR增加,亚临界稳定裕度ζ减小;1.16≤ICR≤1.25内,随着ICR增加,亚临界稳定裕度增大。(2)在内收缩比为1.08的条件下,马赫数变化引起的分离激波角和分离包再附压升两个关键因素变化共同主宰着进气道亚临界稳定裕度的变化趋势。(3)总体上,根据稳定亚临界初始状态的三相点无量纲高度?b是否大于1可将进气道的亚临界稳定裕度变化情形分为两类,当?b<1时,ζ随着?b的增加而减小;当?b> 1时,ζ随着?b的增加而增加。

掺氢对天然气燃烧室燃烧及排放特性影响数值模拟

针对以天然气为燃料的燃气轮机使用掺氢燃料后的燃烧及其排放特性开展研究,基于DLN1.0燃烧室火焰筒,采用数值模拟的方法研究不同掺氢比(H_(2)体积分数0~30%一共7种工况)在恒定热功率和相同当量比条件下对天然气混合气燃烧过程的影响,获得火焰筒内流场、温度场和燃烧产物的分布参数以及对应关系。结果表明:随着掺氢比的增加火焰温度上升,燃烧反应区扩大,火焰筒出口处的温度分布均匀性变差;掺氢造成局部释热量的改变,会导致NO_(x)的排放随着掺氢比的增加而呈现增加趋势;CO和CO_(2)的排放量都有显著的减少,H_(2)O的生成量显著增加。同时,采用所提出稀释燃烧的方法解决由掺氢造成的一系列问题,研究不同当量比工况下掺氢燃烧后的特性变化,并计算得到各个掺氢比工况下最佳的当量比值。研究成果为后续工业燃气轮机天然气掺氢燃烧技术的应用提供了理论指导。

来流总温对液态煤油旋转爆震影响的数值模拟

为了实现煤油/富氧空气旋转爆震燃烧室稳定工作并探索来流总温对流场及爆震燃烧特性的影响,设计了一种液态煤油/富氧空气旋转爆震燃烧室结构,采用欧拉⁃拉格朗日算法开展了旋转爆震燃烧室的冷热态数值模拟。结果表明,随着来流总温的提升,在温度及停留时间的共同作用下,燃油雾化掺混效果并非是来流总温越高越好,而是在1150 K下最优,燃油蒸发率达99.2%,掺混均匀度为50.3%。来流总温超过650 K的条件下均可以实现稳定的旋转爆震工作模式。来流总温的变化对于爆震波的传播模态有着显著的影响,来流总温越大,越有利于液态煤油/富氧空气旋转爆震燃烧室内多波模态的形成。随着爆震波波头数目的增加,单个波头的压力、波速及爆震波高度随之下降,而整体爆震波的稳定性得到了明显的提升。

硼基粉末燃料冲压发动机掺混燃烧特性研究

针对硼基粉末燃料冲压发动机超声速燃烧组织难题,建立气-固两相掺混燃烧方法,开展典型工况(26 km,Ma=6.0)的数值仿真研究,得到了发动机燃烧室内的流动燃烧特性,仿真分析了粉末燃料喷注速度、燃料颗粒粒径以及凹腔结构对燃烧室内气-固两相掺混燃烧情况的影响。结果表明:粉末燃料点火温度是影响燃料掺混燃烧效率的关键因素,当粉末喷注于气相燃烧高温区时,可显著提高燃烧效率;合理的喷注速度有利于增强颗粒与燃气和来流的掺混程度,使得颗粒燃烧更充分;当颗粒粒径从5μm提高至20μm时,射流穿透深度显著增加,粒径5μm时粉末燃烧效率最高,随着粒径增大颗粒点火的难度提高,不利于燃料充分燃烧释热;凹腔结构形成的回流区可以形成较好的点火区域,对于粉末燃料及富燃燃气和超声速来流的掺混起到较好的增益效果,有利于提高燃烧效率。

天然气塔式同轴分级燃烧室掺氢燃烧特性数值模拟研究

为了解天然气掺氢对贫预混燃气轮机性能的影响,采用Chemkin-pro研究了燃料的化学反应动力学特性,对比了不同当量比、掺氢比下的绝热火焰温度、层流火焰传播速度及点火延迟时间,结果表明掺氢能缩短燃料点火延迟时间,增加绝热火焰温度及提高火焰传播速度。进一步以天然气塔式同轴分级燃烧室为研究对象,研究了掺氢比对燃烧室燃烧场分布及燃烧效率、总压损失系数、温度分布不均匀度、一氧化碳及氮氧化物排放量等性能参数的影响。结果表明,随着掺氢比的增加,燃烧效率上升,总压损失系数增加,温度分布不均匀度下降,一氧化碳排放量下降,氮氧化物排放量增加。掺氢比在35%时燃烧室发生回火。在30%~35%掺氢比范围内,燃烧室性能参数变化较大。其中,总压损失系数增幅为24.74%,温度分布不均匀度降幅为31.11%,氮氧化物排放量增幅为416.12%。