进气道喷水对汽油机爆震和缸内燃烧过程影响的仿真分析

以一台1.5 L气道喷射汽油机为研究对象,根据汽油机台架试验结果与喷水器喷雾特性,利用AVL FIRE软件建立了进气道喷水汽油机三维模型,仿真分析了水雾的发展过程与分布状态,研究了4组喷水量对汽油机爆震和缸内燃烧过程的影响规律。结果表明,水雾发展至气门附近即被蒸发,仅有少量水雾以液态形式进入缸内。随喷水量增加,爆震指数降低,降幅达33.70%,缸内温度与压力曲线逐渐向后、向下移动。喷水量为13.186 mg时缸温峰值与不喷水相比下降20.27 K,缸压峰值降低0.48 MPa。缸内进水量低于喷油量的5%时,水雾对爆震和缸内燃烧过程影响微弱。喷水对速燃期影响效果更显著。随喷水量增加,火焰传播速度降低,速燃期延长,累积放热率曲线后移,总燃烧持续期共延长2.5°曲轴转角。     

含氧添加剂DMC对柴油机燃烧与排放特性的影响

分析了各种含氧燃料的物理化学特性对柴油机排放的影响。碳酸二甲酯（DMC）具有含氧量高、沸点高、与柴渍互溶性好等特点，适合作为柴油机的燃料添加剂。测试了纯柴油和含添加剂DMC的柴油机的尾气排放，并进行了燃烧分析。结果表明：添加剂DMC能较大幅度地降低柴油机的碳烟排放，同时使NDx的排放基本保持不变或略有下降；含DMC的燃料滞燃期比纯柴油的长，且燃烧结束的时间早，热效率要比柴油的高，当DMC的添加量为15％时，在不同的工况下，热效率比纯柴渍高1％－3％。     

富氧燃烧对柴油机排放特性的影响

柴油机因其废气中的碳烟排放高而被排除在清洁发动机之外。减少碳烟排放的一种方法是增加缸内空气的氧含量，使燃烧更彻底充分进行。本文介绍了在S195柴油机上进行富氧燃烧试验。对其排放特性进行比较与分析，通过试验研究，找到在富氧条件下同时降低碳烟和NOx排放的方法。     

燃料理化特性对柴油机低温燃烧过程及排放特性的影响

在一台单缸柴油机上,通过柴油掺混20%的正庚烷、正庚烷与异辛烷混合物以及异辛烷与40%正庚烷(体积分数),研究燃料组分、沸点和十六烷值等理化特性对柴油机传统燃烧和低温燃烧影响机理.结果表明,不同十六烷值燃料在高比例EGR下对滞燃期影响更显著;随掺混燃料十六烷值降低,碳烟排放降低;在20%掺混比下混合燃料沸点、黏度等物理特性和燃料组分等化学特性改变对燃烧和碳烟排放影响较小.与20%正庚烷掺混相比,低沸点、低黏度燃料在更高掺混比(40%)下对碳烟排放的降低作用变得明显.大比例EGR低温燃烧下,THC排放明显升高,其中甲烷占总碳氢比例达60%;NO2对整体NOx排放影响很小.在20%掺混比下,燃料理化特性的改变对THC、不同成分HC、CO和NOx排放影响很小;在40%正庚烷掺混比例下,芳香烃排放降低,NOx及NO2排放较柴油升高.     

煤基混合燃料对柴油机燃烧与排放特性影响的研究

在一台高压共轨增压中冷柴油机上研究了煤基混合燃料(33%煤炭提取配方,67%-35#柴油)的燃烧与排放特性。结果表明:相比于燃用-35#柴油,燃用煤基混合燃料时柴油机的燃烧滞燃期基本不变,放热率峰值增大,低转速全负荷时最大缸内燃烧压力降低,而在高转速时变化不大;燃用煤基混合燃料时PM_(2.5)排放物质量浓度降低,全负荷工况下PM_(2.5)排放物质量浓度平均降低约15.2%,部分负荷工况下,低负荷时的改善效果最为明显,平均降低约56.3%;燃用煤基混合燃料时NO_x排放物体积分数略有增大。     

高强化柴油机燃烧过程的优化研究

以某大功率柴油机为研究对象,采用仿真和试验相结合的方法,在保持动力性和经济性不变的条件下,通过燃烧过程优化研究,采用小口径直口ω形1#燃烧室和8×Ф0.42 mm的喷油嘴,将发动机最高燃烧压力从15.5 MPa降低到14.5 MPa以下,提高了发动机的可靠性;将发动机的过量空气系数从2.1降低到1.9以下,缩小了空气滤的体积,降低了整车的重量,提高了车辆的机动性和灵活性.     

喷射参数对柴油机燃烧与排放特性的影响

在一台共轨柴油机上进行了喷射压力、喷射定时、后喷量及后/主间隔角等喷射参数影响作用的试验研究,利用FIRE软件数值模拟获取微观场变化信息,综合分析了喷射参数对缸内燃烧与有害排放物生成的影响机理及规律.结果表明,提高喷射压力和提前喷射定时有利于改善燃油经济性及碳烟排放,但在喷射压力较高(120～130,MPa),喷射定时提前到上止点前2°CA时,再提前喷射定时对碳烟的影响不大,而NOx的生成量显著增加,同时会引起燃烧粗暴.当后/主间隔角一定(15°CA),后喷量为1.5～2.0,mg时,烟度值达到最低,降幅为28%左右;后喷量为1.5,mg时,后/主间隔角在25,oCA附近,烟度达到最低,降幅达到20%.因此,引入后喷时需要选取适当的后/主间隔角和后喷油量,既要增强后喷燃油对缸内流场的扰动效果,使得更多的氧气进入主喷的燃烧产物区,加速碳烟的氧化又要避免进入高温缺氧区域内的后喷燃油量过多以及燃烧过于拖后等负面影响.     

柴油/甲醇组合燃烧发动机的燃烧特性与排放

对一台高速直喷式柴油机采用柴油／甲醇组合燃烧方式及其纯柴油燃烧方式的燃烧特性进行了研究。其结果表明，采用柴油／甲醇组合燃烧的发动机，燃烧始点晚于采用纯柴油时的燃烧起点，但是燃烧速度快，气缸峰值压力比燃烧纯柴油时高；与纯柴油的双峰放热规律不同，组合燃烧的放热率曲线呈单峰形；组合燃烧的最高燃烧温度比燃烧纯柴油时有所降低．进而从燃烧理论上解释了采用组合燃烧可以同时降低碳烟和NOx排放的原因。     

进气初始条件对柴油机低温燃烧及PAHs排放特性的影响

应用三维CFD模型耦合化学动力学模型的方法,研究了进气初始条件对柴油机低温燃烧及多环芳香烃(PAHs)排放特性的影响规律。结果表明:进气温度降低,滞燃期延长,同时由于进气密度增大,使柴油机的循环进气量增多,空燃比升高,燃油在缸内燃烧更充分,在较低的进气温度工况时缸内生成PAHs各组分相对较低;进气压力升高,PAHs各组分的生成时刻提前,并且PAHs各组分的含量依次减少。燃烧起始阶段,苯(C6H6)主要分布在燃烧室凹坑附近。在燃烧中期与后期,其主要分布在凹坑壁面附近。     

Effects of Fischer-Tropsch diesel fuel on combustion and emissions of direct injection diesel engine

Effects of Fischer-Tropsch (F-T) diesel fuel on the combustion and emission characteristics of a single-cylinder direct injection diesel engine under different fuel delivery advance angles were investigated. The experimental results show that F-T diesel fuel exhibits shorter ignition delay, lower peak values of premixed burning rate, lower combustion pressure and pressure rise rate, and higher peak value of diffusion burning rate than conventional diesel fuel when the engine remains unmodified. In addition, the unmodified engine with F-T diesel fuel has lower brake specific fuel consumption and higher effective thermal efficiency, and presents lower HC, CO, NO _x and smoke emissions than conventional diesel fuel. When fuel delivery advance angle is retarded by 3 crank angle degrees, the combustion duration is obviously shortened; the peak values of premixed burning rate, the combustion pressure and pressure rise rate are further reduced; and the peak value of diffusion burning rate is further increased for F-T diesel fuel operation. Moreover, the retardation of fuel delivery advance angle results in a further significant reduction in NO _x emissions with no penalty on specific fuel consumption and with much less penalty on HC, CO and smoke emissions. __________ Translated from Chinese Internal Combustion Engine Engineering, 2007, 28(2): 19–23 [译自: 内燃机工程]     

掺混比例和喷射定时对二甲醚-乙醇发动机燃烧和排放的影响

在一台电控共轨发动机上,试验研究了乙醇掺混比例和喷射定时对二甲醚-乙醇混合燃料燃烧及排放的影响。结果表明:随乙醇比例的增加,滞燃期延长,燃烧持续期缩短,最大压力升高率上升。随喷射推迟,滞燃期延长,燃烧相位延后,燃烧持续期在纯二甲醚时延长,而在掺混乙醇时则先延长后缩短,最大压力升高率先下降后上升。掺混乙醇和推迟喷射使预混燃烧比例增加。随喷射推迟,混合燃料的排气温度升高,喷射推迟到上止点后,排气温度随乙醇比例的增加而升高,排气温度高,则废气能量高,增压器增压比大,进气流量大,导致缸内压缩压力升高。在上止点前喷射时,掺混乙醇能使HC和CO排放保持在较低范围的同时,一定程度降低NO_x排放,掺混15%的乙醇较纯二甲醚最大降低约11%NO_x排放。随推迟喷射,NO_x排放降低,最大降幅达52%,在过分推迟燃料喷射时,因热效率低,循环喷射量增加,含15%乙醇混合燃料的NO_x排放会高于纯二甲醚。HC和CO排放随喷射推迟而升高,且升高幅度增大。     

重型车用柴油机燃用乳化柴油的燃烧与排放特性试验研究

在不改变发动机任何参数的情况下,对高压共轨重型车用柴油机分别燃用柴油和乳化柴油的燃烧与排放特性进行了对比试验研究。试验结果表明:与纯柴油相比,乳化柴油在试验工况下着火滞燃期延长,瞬时放热率峰值提高,燃烧持续期变短;缸内最高压力在低负荷时较柴油高,但在高负荷时较柴油低;在全负荷下,相比于柴油,燃用乳化柴油有效功率平均降低了16.90%,但发动机有效热效率平均提高了2.42%;燃用乳化柴油在常用转速1 800 r/min的负荷范围内时,NOx和碳烟排放分别比柴油平均降低了12.77%和58.90%,改善了NOx和碳烟排放的权衡曲线关系;高负荷时,燃用乳化柴油的CO排放减少,但HC排放增加。     

Experimental study of inlet manifold water injection on combustion and emissions of an automotive direct injection Diesel engine

This paper describes an experimental study conducted on a modern high speed common-rail automotive Diesel engine in order to evaluate the effects on combustion and pollutant emissions of water injected as a fine mist in the inlet manifold.     

柴油机高压共轨喷射系统参数对燃烧和排放性能影响的研究

利用AVL-FIRE软件建立TBD234柴油机高压共轨燃烧过程仿真计算模型,通过仿真计算,系统分析了喷射系统主要参数对柴油机高压共轨燃烧和排放性能的影响。最后进行了试验验证,结果表明,仿真值与试验值基本吻合。研究结果为柴油机高压共轨喷射系统参数的优化设计提供了可靠依据。     

Development and validation of a comprehensive two-zone model for combustion and emissions formation in a DI diesel engine

A two-zone model for the calculation of the closed cycle of a direct injection (DI) diesel engine is presented. The cylinder contents are taken to comprise a non-burning zone of air and another homogeneous zone in which fuel is continuously supplied from the injector holes during injection and burned with entrained air from the air zone. The growth of the fuel spray zone, consisting of a number of fuel–air conical jets equal to the injector nozzle holes, is carefully modelled by incorporating jet mixing to determine the amount of oxygen available for combustion. Application of the mass, energy and state equations in each one of the two zones yields local temperatures and cylinder pressure histories. For calculating the concentration of constituents in the exhaust gases, a chemical equilibrium scheme is adopted for the C–H–O system of the 11 species considered, together with chemical rate equations for the calculation of nitric oxide (NO). A model for the evaluation of soot formation and oxidation rates is incorporated. A comparison is made between the theoretical results from the computer program implementing the analysis, with experimental results from a vast experimental investigation conducted on a fully automated test bed, direct injection, standard ‘Hydra’, diesel engine located at the authors' laboratory, with very good results, following a multi-parametric study of the constants incorporated in the various sub-models. Pressure indicator diagrams and plots of temperature, NO, soot density and of other interesting quantities are presented as a function of crank angle, for various loads and injection timings, elucidating the physical mechanisms governing combustion and pollutants formation. Copyright © 2003 John Wiley & Sons, Ltd.     

四气门发动机进气流动特性的数值建模

应用CFD(computational fluid dynamics)对具有两个进气道的JL475发动机气道内三维可压缩湍流流动进行了数值模拟，得出了气阀在不同升程下的进气流量系数；并将计算结果与试验结果进行了比较分析。结果表明所选模型和计算方法正确，说明了可以利用数值模拟计算代替试验测试得到进气门流量系数。     

供油提前角对柴油/水煤浆混合燃料燃烧排放性能的影响

通过柴油机台架试验,分析了供油提前角变化对柴油/水煤浆混合燃料燃烧排放的影响.试验结果表明:当供油提前角调定为18 ℃A时,柴油/水煤浆混合燃料的有效燃油消耗率降低,热效率升高,燃烧持续期最短,增加或减少供油提前角都将延长燃烧持续期;供油提前角变化对柴油/水煤浆混合燃料的排放有较大影响,逐步增大供油提前角(由17到18 ℃A,再到19 ℃A),混合燃烧的烟度排放降低,Nox的排放先降低再升高,CO的排放先升高再降低,HC排放升高.     

Influence of advanced injection timing on the performance and emissions of CI engine fueled with ethanol‐blended diesel fuel

Ethanol has been considered as an alternative fuel for diesel engines. On the other hand, injection timing is a major parameter that sensitively affects the engine performance and emissions. Therefore, in this study, the influence of advanced injection timing on the engine performance and exhaust emissions of a single cylinder, naturally aspirated, four stroke, direct injection diesel engine has been experimentally investigated when using ethanol‐blended diesel fuel from 0 to 15% with an increment of 5%. The original injection timing of the engine is 27° crank angle (CA) before top dead center (BTDC). The tests were conducted at three different injection timings (27, 30 and 33° CA BTDC) for 30 Nm constant load at 1800 rpm. The experimental results showed that brake‐specific energy consumption (BSEC), brake‐specific fuel consumption (BSFC), NO_x and CO₂ emissions increased as brake‐thermal efficiency (BTE), smoke, CO and HC emissions decreased with increasing amount of ethanol in the fuel mixture. Comparing the results with those of original injection timing, NO_x emissions increased and smoke, HC and CO emissions decreased for all test fuels at the advanced injection timings. For BSEC, BSFC and BTE, advanced injection timings gave negative results for all test conditions. Copyright © 2008 John Wiley & Sons, Ltd.     

The effect of HRG gas addition on diesel engine combustion characteristics and exhaust emissions

Extensive studies have been dedicated in the last decade to the possibility to use hydrogen in the dual-fuel mode to improve combustion characteristics and emissions of a diesel engine. The results of these studies, using pure hydrogen or hydrogen containing gas produced through water electrolysis, are notably different.The present investigation was conducted on a tractor diesel engine running with small amounts of the gas—provided by a water electrolyzer—aspirated in the air stream inducted in the cylinder. The engine was operated at light and medium loads and various speeds.It was found that the addition of HRG gas has a slight negative impact, up to 2%, on the engine brake thermal efficiency. Smoke is significantly reduced, up to 30%, with HRG enrichment, while NO_x concentrations vary in both senses, up to 14%, depending on the engine operation mode. A relative small amount of HRG gas can be used with favorable effects on emissions and with a small penalty in thermal efficiency.