Effects of Excess Air Coefficients on Combustion Characteristics of N-butanol by a Constant Volume Combustion Bomb

The effects of excess air coefficients on the combustion characteristics have been experimentally investigated by means of a constant volume combustion bomb.N-butanol was tested as the research fuel at different air-fuel equivalence ratios.Through the discussion of the combustion pressure,the combustion temperature,accumulated heat release,ignition delay and combustion duration,the effects of the excess air coefficient on combustion characteristics is clarified.Experimental results show that near the theoretical air-fuel ratio,the combustion rate is the fastest accompanying with shorter combustion duration while the combustion pressure and temperature reach the maximum.With increase or decrease of the excess air coefficient the combustion pressure,the temperature and the heat release reduce.Simultaneously,the combustion timing is deferred and the combustion duration becomes longer.

DAMAGE OF A HIGH-ENERGY SOLID PROPELLANT AND ITS EFFECTS ON COMBUSTION

In order to improve the safety of high-energy solid propellants, a study is carried out for the effects of damage on the combustion of the NEPE (Nitrate Ester Plasticized Polyether) propellant. The study includes: (1) to introduce damage into the propellants by means of a large-scale drop-weight apparatus; (2) to observe microstructural variations of the propellant with a scanning electron microscope (SEM) and then to characterize the damage with density measurements; (3) to investigate thermal decomposition; (4) to carry out closed-bomb tests. The NEPE propellant can be considered as a viscoelastic material. The matrices of damaged samples axe severely degraded, but the particles are not. The results of the thermal decomposition and closed-bomb tests show that the microstructural damage in the propellant affects its decomposition and burn rate.

Effects of Medium temperature on lean burn combustion duration of n-butanol

In this study,we did exploratory tests on the combustion duration of n-butanol,of which the object was lean mixture whose excess air ratio is 1.6,the independent variable was the initial temperature of combustion bomb.We did combustion tests on constant volume combustion bomb by changing the boundary conditions of the medium temperature.And we got its influence rules on the combustion duration of n-butanol,analyzing the combustion characteristic parameters about cylinder pressure,pressure rise rate,the combustion temperature,temperature rise rate,heat release and heat release rate.The results show that: With the increasing of medium temperature,the combustion duration is shortened significantly.

乙醇-氢气-空气混合燃气的层流燃烧速度测定

为了研究乙醇的层流燃烧特性,在定容燃烧弹内,分别研究了初始压力为0.3 MPa,氢气比例为50%时,不同初始温度(370 K和450 K)和当量比(0.7~1.4)下,氢气-乙醇混合燃气的火焰传播规律。计算得到了混合燃气的层流燃烧速度和马克斯坦长度,分析了拉伸率对火焰传播速度的影响,同时将研究结果与文献数据进行了比较,验证了计算模型的可靠性。结果表明:随着初始温度的增加,混合燃气的层流燃烧速度也会随之提升;当量比的增加也会提升混合燃气的层流燃烧速度,在当量比为1.2时达到了峰值,随后开始降低。初始温度的增加会在一定条件下会导致火焰的不稳定;在初始温度370 K下,马克斯坦长度始终大于0,火焰一直处于稳定状态;初始温度450 K、0.7~0.9当量比下的马克斯坦长度小于0,火焰出现了不稳定状态,因为较高的初始温度会产生强烈的对流和湍流效应,这些效应会使火焰的边界层受到扰动,造成火焰不稳定;不同初始温度下的马克斯坦长度都随当量比的增加而增加,火焰的稳定性不断提升。对计算得到的层流燃烧速度进行数据拟合,得到了计算乙醇-氢气-空气混合气层流燃烧速度的关系式。

大空间尺度下预燃室射流火焰发展历程的光学诊断和模拟研究

基于定容燃烧弹,在与大型低速预燃室式双燃料船机相似的空间和热力学条件下,采用相似的点火过程,对主燃烧室内的射流火焰发展和引燃预混火焰的扩展历程进行光学测试;提出一种基于全网格映射,分阶段采用不同的燃烧模型的方法模拟不同燃烧阶段的火焰发展过程。基于定容装置试验数据验证了模型对燃烧火焰扩展速度预测的适用性和准确性。研究结果表明:预燃室燃油喷射量直接影响射流火焰的最大贯穿距离和火焰强度;主燃烧室内的混合气需要达到一定浓度才能被引燃。对燃烧过程的模拟,第一阶段燃烧采用均质搅拌反应器(well-stirred reactor,WSR)模型可以较为准确地模拟不同燃油喷射量下的射流发展速度和火焰射流的最大贯穿距离;第二阶段燃烧采用G方程可以较为准确地模拟火焰在各方向上的扩展速度。采用Mapping方法连接的两个模型对燃烧两个阶段的火焰扩展的整体速度具有较高的预测精度。

Influence of Mixture Gas Conditions on the Laminar Combustion Characteristics of Natural Gas

Natural gas is a promising alternative fuel for the internal combustion engine,and natural gas engine has become an efficient and feasible measure to deal with the energy shortage and climate change.Since the laminar flame characteristics are the foundation of the turbulent flame,the laminar flame characteristics of natural gas have a significant impact on the combustion status and efficiency of the engine.A visual constant volume bomb was used to study the influence of the gas components,different excess air coefficient(λ),and initial conditions on the laminar combustion characteristics of natural gas.The experimental results showed that when the initial pressure and temperature were 0.1 MPa and 300 K respectively,compared to propane,ethane had a remarkable influence on the equivalent-combustion laminar-combustion-speed,with an average increase of approximately 5.1%for every 2.5%increase in the ethane proportion.The laminar combustion velocity of the natural gas under different excess air coefficients had a maximum value at aboutλ=1.0,and the Markstein length of the flame decreased with the increase of theλ.The increase in the initial pressure of the mixture resulted in a decrease in the equivalent-combustion laminar-combustion-speed of the flame,a significant decrease in the Markstein length.The increase of the initial temperature of the mixture led to a rapid increase of the equivalent-combustion laminar-combustion-speed,but the effect on the flame Markstein length was not dominant.

纳米CuBi_(2)O_(4)/G复合增强AP/nAl复合物燃烧和释压研究

为了显著提高AP/nano-Al(nAl)复合物的压力释放效率,降低燃烧时间,提出了一种制备AP/nAl/G/CuBi_(2)O_(4)(CBO)复合物的策略。密闭爆发测试结果表明,复合物的压力释放率和压力达到峰值时间都得到了显著改善;当添加石墨烯(G)(2 wt%)/CBO(5 wt%)时压力增加13.5%,增压速率增加51.1%。此外,利用激光点火装置和高速摄像系统对制备复合物的点火和燃烧性能进行了评估,结果表明G和CBO的引入成功降低了点火延迟并缩短了20 ms燃烧时间。综上所述,添加CBO和G能显著改善AP/nAl燃烧放热、峰值压力与最大增压速率。

氧弹燃烧-离子色谱法测定助焊剂中的碘

采用氧弹燃烧-离子色谱法测定助焊剂中的碘。使用NaOH-抗坏血酸(AA)复合成分作为吸收液有效成分,可将氧弹燃烧对碘的吸收率达到90%左右,并且能有效解决以单一AA成分作为吸收液有效成分氧弹燃烧后,样品在进行离子色谱测试时基线过高而不能准确识别碘的问题。实现碘含量在50~1000μg范围内助焊剂样品碘的高效吸收以及准确测定。方法安全,环保,操作便捷,在助焊剂中碘含量的准确测定方面可发挥重要作用。

氧弹燃烧-离子色谱法测定4种再生醇溶剂中总氯、氮和硫的含量

建立并优化了甲醇、乙醇、异丙醇与正丁醇等4种再生一元醇中总氯、总氮与总硫含量的测定方法。采用氧弹燃烧的样品前处理方法,以25 mmol/L的氢氧化钠溶液为氧弹内吸收液,目标物转化为相应的离子化合物,使用离子色谱法进行定量。结果表明,方法中总氯、总氮与总硫拟合的标准曲线,其线性相关系数均大于0.999;样品取样量为1.5 g时,总氯、总氮与总硫的检出限分别为4.79 mg/kg、15.0 mg/kg与6.33 mg/kg,测定下限分别为19.2 mg/kg、60.0 mg/kg与25.3 mg/kg,RSD在2.58%~3.05%之间,加标回收率在70.6%~119%之间。该方法操作简单、准确度较高,实现了甲醇、乙醇、异丙醇与正丁醇等4种再生产品中总氯、总氮与总硫含量的同步快速测定。

氧弹燃烧离子色谱法同时检测焚烧废弃物中氟、氯、溴、硫多元素含量

采用氧弹燃烧离子色谱法同时检测焚烧废弃物中氟、氯、溴、硫含量。进行了方法检出限测试、标准物质测试、实际样品测试、标准样品加标回收实验验证方法准确度和精密度研究。4种元素的方法检出限在1.4~13.8 mg/kg、方法加标回收率在91.4%~105.5%、测定值的相对标准偏差<4.5%。氧弹燃烧离子色谱法检测焚烧废弃物中氟、氯、溴、硫含量准确度高,方法可行。

氧弹燃烧-离子色谱法测定精馏残渣中硫的含量

水泥窑协同处置危险废物精馏残渣中硫元素含量的常用测定方法存在操作繁琐、灵敏度低、测试条件要求高、环境污染严重等问题。采用“氧弹燃烧—离子色谱法”测定精馏残渣中硫元素含量,克服了常规检测方法的不足,提高了检测结果的准确性及重现性。硫含量分析检测实验表明,在氧弹燃烧压力3MPa,吸收液为0.5mol/L NaOH溶液,吸收液作用时间20min,流动相流速100mL/min的条件下,硫酸根的质量浓度在0.5~50mg/L范围内表现出了较好的线性关系,相关系数均>0.999,平均加标(添加标准溶液)回收率达96.8%。

Burning characteristics of microcellular combustible objects

Microcellular combustible objects for application of combustible case,caseless ammunition or combustible detonator-holding tubes are fabricated through one-step foaming process,in which supercritical CO_2 is used as foaming agent.The formulations consist of inert polymer binder and ultra fine RDX.For the inner porous structures of microcellular combustible objects,the cell sizes present a unimodal or bimodal distribution by adjusting the foaming conditions.Closed bomb test is to investigate the influence of both porous structure style and RDX content on burning behavior.The sample with bimodal distribution of cell sizes burns faster than that with unimodal distribution,and the concentration of RDX can influence the burning characteristics in a positive manner.In addition,the translation of laminar burning to convective burning is determined by burning rate versus pressure curves of samples at two different loading densities,and the resulting transition pressure is 30 MPa.Moreover,the samples with bigger sample size present higher burning rate,resulting in providing deeper convective depth.Dynamic vivacity of samples is also studied.The results show that the vivacity increases with RDX content and varies with inner structure.

高压甲烷射流冲击预混火焰过程中涡量的变化

基于CONVERGE软件开展三维仿真计算,分析了定容燃烧弹内高压甲烷射流撞击当量比为1的预混气体燃烧过程中的涡量变化特征.根据射流前锋面与火焰的位置关系,将火焰发展全过程分为射流前峰面未接触火焰阶段、进入火焰阶段和离开火焰阶段3个阶段.相比于自由射流贯穿速度,在射流进入火焰阶段射流燃烧平均贯穿速度显著增加,并大于自由射流的贯穿速度和预混燃烧速度之和.产生此结果的原因是此阶段动量参数涡量的大幅增加;在轴向距离为40 mm处、火焰发展时间为1.6 ms时,射流燃烧模式平均涡量值与自由射流模式差值最大,约为260 s^(-1),是此时此截面预混燃烧模式平均涡量值6 s^(-1)的43倍.

柴油双喷射撞击喷雾和燃烧可视化研究

利用高速相机基于纹影法获取上置喷油器和侧置喷油器在单独喷射和垂直喷射状态下的喷雾和燃烧火焰发展图像。柴油喷射压力设置为80、120、140 MPa,环境背压设置为4 MPa,环境温度在喷雾和燃烧研究中分别设置为500 K和800 K。结果表明:随着喷射压力的增加,不管是单独喷射还是垂直喷射,喷雾贯穿距和面积均增大;垂直喷射状态下,两油束碰撞后损失部分能量,导致其喷雾面积小于两单独喷射状态下的喷雾面积之和。采用双色法研究不同工况下燃料燃烧特性,结果表明:在喷射后1.50~3.50 ms的燃烧稳定时期内,随着喷油压力的提高,各喷射状态下的火焰面积均增大,燃烧温度提高,碳烟生成量降低;垂直喷射状态下的火焰面积小于两单独喷射状态下的火焰面积之和,燃烧温度和碳烟生成量均高于两单独喷射状态。

基于定容燃烧弹的正丁醚压力振荡特性试验研究

基于定容燃烧弹实验平台,在环境压力为0.05~0.20 MPa、温度为423~453 K、当量比为0.7~1.6条件下开展正丁醚的压力振荡特性试验研究,获得正丁醚燃烧过程中的燃烧压力、火焰形态、燃烧弹振动、声压实验数据并对其进行分析。研究结果表明:正丁醚在较低温度、较高压力下,当量比为1.5左右时产生的压力振荡强度最大,燃烧过程中的压力、振动、声压、亮度等信号具有相同的变化规律,均呈现出随温度增加缓慢降低、随压力增加显著增强、随当量比增加先增后减的趋势。随着压力振荡强度增大,振荡的主频向高频方向移动。正丁醚的火焰不稳定性与压力振荡的产生存在一定关系。

氧弹法测量硼粉燃烧热值的方法学研究

硼是一种高能固体燃料,其燃烧热值的准确测定十分重要。用甲醇-水混合溶剂洗脱去除硼粉表面的氧化物,然后用氢氧化钠溶液滴定洗脱液中硼酸含量,计算得到500nm原始硼粉表面氧化层平均厚度为1.8~5.5nm,40nm原始硼粉表面氧化层平均厚度0.5~1.6nm,采用氧弹法测定了500nm和40nm原始硼粉及其去除氧化物后的燃烧热值,通过滴定法分析燃烧产物中硼酸含量,换算得到实际燃烧的单质硼质量,从而计算出单质硼燃烧热值。实验结果表明,500nm原始硼粉及其去除氧化物后燃烧得到的单质硼平均燃烧热值分别为55.2±0.8kJ·g^(-1)和55.4±1.2kJ·g^(-1),两者非常接近,且落在文献值范围内;40nm原始硼粉及其去除氧化物后燃烧得到的单质硼平均燃烧热值分别为53.3±0.9kJ·g^(-1)和51.6±0.9kJ·g^(-1),略低于文献值。为了准确测量单质硼的燃烧热值,宜选择颗粒尺寸较大(如500nm)的硼粉样品。在上述厚度范围内,氧化层对500nm原始硼粉或40nm原始硼粉的燃烧效率均无影响。当硼颗粒的尺寸为40~500nm时,燃烧效率也与硼颗粒的粒径大小无关。

Numerical evaluation of acoustic characteristics and their damping of a thrust chamber using a constant-volume bomb model

In order to numerically evaluate the acoustic characteristics of liquid rocket engine thrust chambers by means of a computational fluid dynamics method, a mathematical model of an artificial constant-volume bomb is proposed in this paper. A localized pressure pulse with a very high amplitude can be imposed on specified regions in a combustion chamber, the numerical procedure of which is described. Pressure oscillations actuated by the released constant-volume bomb can then be analyzed via Fast Fourier Transformation（FFT）, and their modes can be identified according to the theoretical acoustic eigenfrequencies of the thrust chamber. The damping performances of the corresponding acoustic modes are evaluated by the half-power bandwidth method. The predicted acoustic characteristics and their damping for a special engine combustor agree well with the experimental data, validating the mathematical model and its numerical procedures. A small-thrust liquid rocket engine chamber is then analyzed by the present model. The First Longitudinal（1L） acoustic mode can be excited easily and is hard to be damped. The axial position of the central constantvolume bomb has little influence on the amplitude and damping capacity of the First Radial（1R） and 1L acoustic modes. Tangential acoustic modes can only be triggered by an off-centered constant-volume bomb, among which the First Tangential（1T） mode is the strongest and regarded as the most harmful one. The amplitude of the 1L acoustic mode is smaller, but its damping factor is larger, as a constant-volume bomb is imposed approaching the injector face. These results are contributed to evaluate the acoustic characteristics and their damping of the combustion chamber.

共轴聚焦型微流控装置剪切高粘溶液连续制备双基球形发射药

为了探索连续化生产粒径可控的百微米范围内双基球形发射药工艺条件,以质量分数为10%的双基发射药溶液为分散相,采用共轴聚焦型微流控装置制备了400~700μm范围内粒径可控的双基球形发射药,并研究了两相流量比(Q_(c)/Q_(d))、芯片尺寸对其粒径和形貌的影响。通过扫描电镜、光学显微镜、密闭爆发器等测试方法,表征了样品形貌、粒径分布和定容燃烧性能。结果表明:随两相流量比(Q_(c)/Q_(d))减小,相同芯片下制备样品的中位粒径(D_(50))先增大后减小;随芯片的连续相或分散相通道内径增大,相同两相流量比下制备样品的D50依次增大。当分散相通道内径为0.85 mm,连续相通道内径为2.00 mm,两相流量比为200.00时,制备的样品单分散性好、表面光滑、内部密实、球形形状规则(平均球形度φ_(K)=0.949)且粒径分布窄(跨度span=0.09),其D50为539.94μm,平均颗粒密度ρ为1.601 g·cm^(-3)。密闭爆发器实验中,压力⁃时间曲线表明球形样品在2种装填密度(Δ_(1)=0.12 g·cm^(-3)、Δ_(2)=0.20 g·cm^(-3))下能稳定燃烧,动态活度⁃相对压力曲线符合密实球形药减面燃烧规律。

Spray,atomization and combustion characteristics of oxygenated fuels in a constant volume bomb:A review

Biofuels have extensive available resources and have an immense potential as promising alternative fuels for automobile.The application advantages of biofuels are mainly reflected as particulate matter(PM)reduction,carbon neutral,greenhouse gases reduction,waste utilization,energy and economic security,and fuel pluralism.Based on the understanding of molecular structure effects of biofuels on soot formation and particles morphology,the effects of alcohols,ethers,esters and biodiesel on spray and combustion process in constant volume bomb in recent years are retrospectively analyzed in this paper.For the mixture,macromolecular ester fuels and polyoxymethylene dimethyl ether(PODE)are conducive to the improvement of liquid spray,while biodiesel,small molecules,dimethyl ether(DME)and alcohols are reversed.Alcohols are advantageous to the extension of mixing time and the increasing of vapor-phase mixture.Through the influence integrated assessment,alcohols show the best performance on the spray,atomization and combustion,while biodiesels show the worst.But in terms of combustion,PODE is the best choice without considering spray and atomization.For binary alternative-diesel fuel blends,methanol or butanol is the best additive based on synthetically considerations on spray,atomization and combustion.To meet the requirements of the fuel application of diesel engine,ternary fuel or even quaternary fuel have been proposed and explored.This review can help to form a systematic understanding on fuel recombining and obtain the guide of clean and efficient fuel formulation for diesel engine.

氢气乙醇混合物层流燃烧速度及火焰不稳定性研究

氢气是一种高效的添加剂,可改善乙醇燃料的燃烧特性,为更好地应用于燃烧装置,有必要研究其层流燃烧特性。在初始压力为0.1及0.4 MPa,初始温度为400 K,等效比范围为0.7~1.4,氢气比例为20%、50%和80%下进行实验,采用定压法(constant pressure method,CPM)得到层流燃烧速度(laminar burning velocity,LBV)。对火焰发展不同阶段的火焰形貌进行研究,当火焰表面的大裂纹分裂出现小裂纹,并导致新细胞再生时,火焰变得不稳定;还研究流体动力学效应和热扩散效应对火焰固有不稳定性的影响。结果表明:LBV随着氢气比例的增加而增加,在富氢状态下其提升效果更加显著;流体动力不稳定性随着压力的增加而增加,热扩散不稳定性对压力变化不敏感;此外,增加氢气比例或初始压力将使火焰更早变得不稳定。