CO2缸内喷射对柴油准HCCI燃烧排放特性的影响

用开发的气体喷射系统,研究了缸内喷射CO2对两段喷油实现的准均质压燃(HCCI)燃烧排放的影响.结果表明:通过调节CO2的喷射始点和喷射量,可以有效控制NOx排放.随着缸内CO2喷射始点的提前,燃烧相位推迟,NOx排放降低.在缸内喷射始点为-150℃A ATDC时,随着CO2循环喷射量的增大,缸内最高平均温度降低,燃烧相位推迟,最大压力升高率和指示热效率变化不大,而出于滞燃期的增大,放热率峰值反而比原机略高;NOx排放减小,HC和CO排放增大,烟度变化比较小.     

后喷时刻对柴油机燃烧影响的可视化研究

后喷可改善柴油机的颗粒物排放特性。在光学发动机上,保持总喷油量不变,变换不同主、后喷间隔时刻,对缸内燃烧过程进行高速摄影,研究后喷时刻变化对柴油机缸内燃烧特性的影响。将获取的缸内燃烧火焰图像,利用双色法计算得出缸内温度场和表征碳烟浓度的KL因子分布情况,并分析缸内燃烧温度和碳烟生成特性。研究表明,随主、后喷间隔角增加,温度分布及KL因子总量呈双峰分布,KL因子总量后期减少速度增加,即碳烟氧化速度加快。     

喷雾撞壁后近壁区域火焰发展及碳烟生成研究

本文基于多尺度液滴撞壁形态提出了新的考虑了不同飞溅状态的撞壁模型。结合容弹实验研究了近壁区域喷雾撞壁后火焰发展过程,对影响近壁区燃烧过程及碳烟生成规律的边界温度进行了探讨。结果表明,环境温度和壁面温度对喷雾撞壁后的液膜沉积量以及后续的燃烧过程影响显著。碳烟产生峰值直接和壁面燃油沉积量呈正相关,而较高的近壁区域温度可加速燃油蒸发并减少燃油沉积量。燃油沉积量的不同,其火焰发展形式不同:当沉积燃油较少时,近壁混合气形成较快,从而维持了稳定的燃烧过程;而当沉积燃油较多时,近壁区域的燃烧呈现不稳定的池火过程。随着环境温度和壁温的增加,油膜燃烧时刻提前并形成可燃混合气,从而加速了碳烟的生成和氧化。     

乙醇与汽油的喷雾及蒸发特性研究

随着汽车发动机的发展,缸内直喷汽油机(GDI)逐渐成为关注和研究的重点。液体燃料喷雾的结构和蒸发与直喷汽油机内燃烧的稳定性、发动机效率以及尾气排放有着密切联系。本文通过纹影测试技术对乙醇和汽油的直喷喷雾的雾化和蒸发进行测试,研究结果表明环境温度、环境压力和喷射压力对喷雾贯穿距有着显著的影响,而燃油温度在低于燃油沸点时对喷雾贯穿距影响很小。因此可以通过控制环境温度和压力,以及燃油的喷射压力和温度对喷雾贯穿距进行优化.     

VGT开度对汽/柴油双燃料发动机燃烧过程的影响

基于一台增压柴油发动机,在进气道增加汽油喷射系统,实现进气道预混喷射汽油,缸内直喷柴油压燃的燃烧模式,通过调节VGT(Variable Geometry Turbocharge)开度改变增压压力,对汽/柴油双燃料发动机的燃烧过程进行深入研究。研究结果表明:一定限度内VGT开度的提高使得增压压力变大,可以使缸内的充量密度变大,局部当量比下降,放热速率变缓,使缸内燃烧趋近于低温燃烧,且适当提高柴油喷射共轨压力,可以有效提高混合气的燃烧速率;增压压力主要影响第一次喷射的柴油燃烧;在1800 r/min_145 Nm的工况点,随着VGT开度的增大,样机氮氧化物和碳烟排放均降低,燃烧循环变动和泵气损失对油耗的影响呈现先降后升的趋势,在0.16 MPa左右达到最低。     

乙醇柴油混合燃料碳烟特性可视化研究

在一台电控共轨光学发动机上,采用高速摄影法,对不同掺混比例的乙醇柴油混合燃料进行研究,获取了缸内燃烧火焰图像,通过双色法得到表征碳烟总体分布的KL因子,分析了乙醇这种含氧生物质燃料对缸内燃烧过程和碳烟生成特性的影响。研究结果表明,随着乙醇掺入比例的增加,滞燃期相对延长,燃烧持续期缩短,火焰的亮度和分布面积都随之下降。KL因子的最高浓度降低,碳烟浓区的分布区域减小,碳烟的氧化进程加快。     

直喷式柴油机燃烧数值计算研究

以KIVA-3为计算平台,对4气门直喷式柴油机的早喷燃烧、预喷燃烧和传统燃烧三种燃烧方式工作过程进行了模拟计算,得以下结论:早喷燃烧方式因喷到缸壁的油量较多,受进气涡流影响较少,同时利用喷射效应改善缸内氧气分布,因此早喷燃烧比较完全。预喷燃烧方式仍以扩散燃烧为主,预喷油燃烧改变了主喷初期油注周围的组分分布与温度分布,从而改变主喷燃油的燃烧历程。进气涡流造成的缸内流场不均匀性是影响传统燃烧方式燃烧不完全的主要因素之一。     

DMM及纳米颗粒添加剂对农用柴油机燃烧与排放性能的影响

本文通过在柴油中添加小比例二甲氧基甲烷(DMM)以及纳米氧化铝(Al2O3)颗粒研究一台小型农用柴油机的燃烧与排放特性.研究表明,随着柴油中DMM添加比例的增大,发动机燃烧特性参数如缸内压力、燃烧放热率及制动热效率得到明显地提升,着火延迟期以及CA50逐渐减小;排放方面HC和NOx增加,而CO和碳烟得到有效地抑制.燃油...     

柴油燃料HCCI燃烧影响因素的试验研究

本文采用在进气上止点附近进行柴油喷射,利用缸内高温残余废气促进燃油蒸发形成均质混合气,实现了柴油燃料的均质压燃(HCCI)。试验结果表明柴油燃料HCCI燃烧的放热规律呈现低温和高温放热两个阶段,并且NOx排放可以降低95%-98%。本文主要研究了影响HCCI燃烧的因素,指出负荷增大、进气温度增加和负气门重叠期的增加使HCCI着火提前,而外部EGR率的增大可以推迟着火。因此对于低温自燃性好的燃料,冷EGR是控制其HCCI着火燃烧过程的有效措施。     

直喷式柴油机燃烧过程及碳烟生成的初步计算

依据已简化的包含多环芳烃生成的正庚烷气相详细化学反应机理,基于专业流体解析软件FLUENT6.3对直喷式柴油机压缩、膨胀冲程内的自燃和燃烧过程进行了动态模拟,得到了缸内平均温度、主要反应物以及中间产物多环芳烃生成量随转角变化的特性曲线.在数值上,计算得到以苯环质量为主的多环芳烃总生成量水平比试验测量结果约高出1~2个量级,但是在随转角变化的特性上,计算与试验测量曲线定性趋势一致.针对特定转角时刻主要火焰结构参数的截面分布,分析研究了柴油机缸内化学反应特性与流体流动相互作用下的空间分布特征.通过耦合详细碳烟粒子动力学模型,对碳烟表象尺寸进行了初步模拟.     

DMM燃料柴油机可控预混合燃烧的研究

本文介绍了在压燃式发动机上进行的预混合燃烧研究。在柴油机的进气道入口处安装了一个电控燃料喷射系统,喷入具有低十六烷值、低沸点的甲缩醛(DMM)燃料,在压缩冲程中形成均匀的混合气,并在上止点附近喷入少量柴油来点燃混合气。本文研究了预混合燃料比、发动机负荷、进气中CO2浓度和喷孔直径对发动机燃烧和排放的影响。试验结果表明,进气道喷射DMM的预混合燃烧能同时大幅降低NOx和碳烟排放,为降低柴油机有害排放提供了一种新途径。     

燃烧驱动气动CO2激光器几种液体燃料性能差异的数值模拟

 在甲苯、苯、煤油和乙醇四种不同液体燃料燃烧驱动条件下,对气动CO₂激光器燃烧室的平衡组分、小信号增益沿流场方向的分布及激光器的输出功率进行了数值模拟,计算对比分析了该四种燃料的性能。计算结果表明甲苯是气动CO₂激光器四种燃料中最为理想的燃料。     

Effect of ultrasonic irradiation on the properties and performance of biodiesel produced from date seed oil used in the diesel engine

In the present study, the effect of ultrasound irradiation on the transesterification parameters, biodiesel properties, and its combustion profiles in the diesel engine was investigated. Moreover, date seed oil (DSO) was firstly utilized in the ultrasound-assisted transesterification reaction. DSO was extracted from Zahidi type date (Phoenix dactylifera) and was esterified to reduce its Free Fatty Acid (FFA) content. Biodiesel yield was optimized in both heating methods, so that the yield of 96.4% (containing 93.5% ester) at 60 °C, with 6 M ratio of methanol/oil, 1 wt% of catalyst (NaOH) and at 90 min of reaction time was reported. The ultrasound irradiation did not influence the reaction conditions except reaction time, reduced to 5 min (96.9% yield and 91.9% ester). The ultrasonic irradiation also influenced on the physicochemical properties of DSO biodiesel and improved its combustion in the diesel engine. The analysis results related to the engine and gas emission confirmed that the ultrasound-assisted produced biodiesel has lower density and viscosity, and higher oxygen content facilitating injection of fuel in the engine chamber and its combustion, respectively. Although, B40 (biodiesel blend consisting of 40% biodiesel and 60% net diesel fuel) as a blend of both fuels presented higher CO₂ and lower CO and HC in the emissions, the DSO biodiesel produced by ultrasound irradiation presented better specifications (caused about 2-fold improvement in emissions than that of conventional method). The findings of the study confirmed the positive effect of the ultrasound irradiation on the properties of the produced biodiesel along with its combustion properties in the diesel engine, consequently reducing air pollution problems.     

Sonochemical reduction of carbon dioxide

Sonolysis of carbon dioxide dissolved in water was performed from a standpoint of reducing this material in atmosphere. During one hour of sonication, the amount of CO2 decreased to about half at 5 degrees C under CO2-Ar atmosphere. The decreasing rate for CO2 followed the order Ar > He > H2 > N2 and it was down with increasing temperature in the range of 5-45 degrees C. The most favorable concentration for reducing CO2 was 0.03 (mole fraction of CO2 in gas phase). This concentration in gas phase means an equal mixture of CO2 and Ar in water, because CO2 is more soluble than Ar. Since carbon dioxide dissolved in water would be partly ionized, the roles of ions on the sonolysis were also examined. Gaseous reaction products were CO, H2 and a small amount of O2. Carbon monoxide and hydrogen might be obtained from CO2 and H2O by sonolysis, respectively. Both gases are fuel and react each other to C1 compounds such as methanol, and so on. Therefore, irradiation of ultrasonic waves should be an important technique for reducing CO2.     

自发喇曼散射技术对燃烧场的诊断

 介绍了利用Nd:YAG激光的三倍频激发自发振动喇曼散射技术对燃烧场的诊断及相关的实验原理，测量了不同配比条件下的CH₄-air预混火焰内的主要组分(N₂，O₂，H₂O，CH₄)及其相对浓度；并分别用分子浓度测温法和斯托克斯谱与反斯托克斯谱强度比法测量了火焰的温度；还对该技术测温、测浓度的不确定度进行了分析。将该技术应用到对复杂的固体燃剂燃烧场的诊断，取得了燃烧场中几种主要燃烧组分（N₂，H₂CO，CH₄，H₂O）的喇曼光谱，以及这些组分在燃烧过程中的变化信息。     

四气门发动机可变涡流稀薄燃烧特性研究

本文研究了可变涡流对四气门发动机稀薄燃烧特性的影响情况。在稀薄燃烧情况下,发动机负荷大小对CO和HC排放的影响不大,对NOx排放的影响主要表现在对13～17空燃比范围内NOx排放的影响,负荷越大,NOx排放越大;对空燃比小于13或大于17以后的NOx排放影响较小。阀片位置对发动机排放特性的影响较小,对发动机的燃油经济性存在一定影响,这是因为不同阀片位置的进气涡流比不同所致,同时也表明较强的涡流运动对燃油经济性更有利。涡流运动在不同转速条件下对发动机燃油经济性的影响情况不同,它更有利于改善低速条件下的燃油经济性。     

自发喇曼散射技术对燃烧场的诊断

介绍了利用Nd:YAG激光的三倍频激发自发振动喇曼散射技术对燃烧场的诊断及相关的实验原理,测量了不同配比条件下的CH4-air预混火焰内的主要组分(N2,O2,H2O,CH4)及其相对浓度;并分别用分子浓度测温法和斯托克斯谱与反斯托克斯谱强度比法测量了火焰的温度;还对该技术测温、测浓度的不确定度进行了分析。将该技术应用到对复杂的固体燃剂燃烧场的诊断,取得了燃烧场中几种主要燃烧组分（N2,H2CO,CH4,H2O）的喇曼光谱,以及这些组分在燃烧过程中的变化信息。     

Gasification of carbon-bearing raw materials in plasma-arc electric furnace with heater and risk of explosion in syngas mixtures

Saw dust was gasified at combined and separated impact of the heater and arc discharge on the raw material. It is shown that because of combustion of a part of produced syngas in the heater the raw material can be gasified with power inputs reduced by 20–25 % in comparison with plasma gasification. Data on parameters of combustion and detonation of syngas mixtures with oxygen and air at a change in the ratio between fuel components CO and H₂ and between fuel and oxidizer are shown for the first time.     

正庚烷复合均质压燃的燃烧与排放特性研究

本文对参比燃料正庚烷(n-heptane)在一台单缸柴油机上进行了复合均质压燃试验,在缸内直喷正庚烷的同时使用电控燃油喷射系统控制进气道的正庚烷喷射量,以达到控制和改善HCCI着火和燃烧的目的.研究了常温常压下,不同预混合比例和不同负荷的正庚烷复合HCCI燃烧和排放特性.研究发现:在保持NOx排放较低的情况下(100×10-6),这种燃烧方式可以有效的拓宽HCCI的运行范围,大幅降低HC排放(平均降低1/3),同时对降低小负荷时的CO排放也有明显效果.     

New advanced in situ carbon monoxide sensor for the process application

Mixed potential solid electrolyte CO sensors with sensing electrodes based on composite with various semiconducting oxides were extensively studied in the temperature range 500–650 °C for sensitivity, stability and cross-sensitivity besides CO to other combustion components like CO₂, H₂O, O₂, and SO₂. The highest CO sensitivity was found for the CO sensor with composite electrode based on Au/Ga₂O₃ showing also good reproducibility and stability in hazardous combustion environment. CO sensor response behavior in non equilibrated oxygen containing gas mixtures is mainly determined by the catalytic activity of the measuring electrode and depends strongly on preparation and measuring conditions. Mixed oxides based on doped chromites show only a little sensitivity to CO. CO sensor based on Au/Ga₂O₃ composite electrodes was showing good CO selectivity in the presence of other combustion gas species and finally was tested in combustion environment at power plant. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.