天然气缸内直喷是当前的热点技术之一，研究其射流特性及射流卷吸规律对优化直喷天然气发动机有重要意义．建立了三维模型，开展了高压甲烷气体在圆形单喷孔中的射流特性三维仿真研究，并结合质量流量和贯穿距离试验结果验证了模型；研究了入口压力为5、10 和20 MPa、背压为2MPa 时喷嘴内流动以及气体射流的变化规律．结果表明：喷嘴出口处射流速度达到音速时，出现速度雍塞；根据气体射流平均速度发展趋势，喷嘴外气体射流可分为两个区域：喷嘴近端区域，气体离开喷嘴迅速膨胀，形成马赫盘，导致该区域气体射流速度迅速下降；喷嘴远端区域，马赫盘消失，气体膨胀作用较小，气体射流速度趋于平缓；在近喷嘴端区域，射流天然气对背景气体的卷吸能力较强，气体射流区域的质量流量增加率较大，而在喷嘴远端区域，卷吸能力减弱，射流区域的质量流量变化不大．因而可知高压甲烷射流特性及其对背景气体的卷吸影响作用有助于研究直喷天然气缸内混合过程．

采用在压缩行程上止点前向燃烧室内直接喷入一定量机油液滴，模拟了悬浮在燃烧室内的机油液滴引燃可燃混合气诱发低速早燃(LSPI)现象的过程．试验验证了选用的计算模型及计算方法的可行性后，数值模拟了不同低速运转条件下、不同乙醇掺混比(体积分数)的乙醇-汽油混合燃料时，小缸径增压直喷发动机燃烧室内由机油液滴引发的低速早燃现象以及后续的超级爆震过程．结果表明：乙醇掺混比分别为10%和20%(E10、E20)时，发动机缸内依次发生了超级爆震燃烧；当乙醇掺混比为30%(E30)时，即使发生了早燃现象(1 200 r/min)并导致随后的爆震燃烧，但压力升高幅度明显降低，此时没有发生超级爆震燃烧；随着发动机转速提高(1 600 r/min)，使用E30 燃料时发动机缸内也仅发生了早燃现象，而没有发生爆震燃烧；当乙醇掺混比高于50%(E50)后，不同工况条件下发动机缸内已经没有低速早燃现象．使用乙醇-汽油混合燃料的小缸径增压直喷发动机在超级爆震发生前一定有低速早燃现象发生，但低速早燃现象不一定导致超级爆震过程．

在雾化激波管中利用反射激波研究了乙醇汽油/空气混合气在高温、低压条件下的自着火特性．测量了混合气在温度为1 100～1 750 K、压力为0.10～0.65 MPa 条件下，燃空当量比为0.2～2.5 时的着火延迟期、着火壁面压力及OH 基自发光强度，分析了当量比、着火温度及压力对混合气自着火特性的影响．结果表明：乙醇汽油/空气混合气的着火延迟期在高温条件下随当量比的增大而延长，不同压力下着火延迟期的对数与着火温度的倒数均呈线性分布，满足Arrhenius 关系，并且在低压范围内着火延迟期对压力的依赖性较高；混合气在当量比为1.0、着火温度为1 300～1 430 K 时发生剧烈爆燃，此时OH 基自发光强瞬间达到峰值后急剧下降，而温度升高后，OH基自发光维持较高强度的时间增长，爆燃压力峰值降低，接近等压燃烧．

针对某6缸重型柴油机排气歧管热机疲劳裂纹故障,采用仿真分析的手段对其失效机理进行了相关研究。研究表明:排气歧管在热机工况下,管身主要承受压应力作用,部分区域由于压应力过大发生塑性变形,在冷机工况时由于发生塑性变形的区域不能自由恢复至原状态,应力状态由压应力转化为拉应力,在这种反复拉压应力作用下发生疲劳失效。排气歧管的热机疲劳寿命采用基于Sehitoglu的热机疲劳理论进行了预测评估。

在GT-SUITE中建立了一维重型柴油机瞬态冷却系统仿真模型,并对冷却系统控制策略的开发方法和控制效果进行了研究。以降低冷却系统附件最小功耗及提高冷却液温度控制精度为目标,分别设计了脉谱前馈与模糊控制、变论域模糊控制、变论域模糊控制加水泵比例积分控制3种控制策略,并在全球统一瞬态试验循环工况下进行发动机台架工况与整车车辆运行工况的仿真计算对比。研究结果表明:相比模糊控制,反馈采用变论域模糊控制能使发动机出口冷却液温度振幅减少37.6%,温度处于±0.5℃区间内的时间增加39.98%,且附件总能耗降低8.58%,冷却性能得到明显改善;额外采用水泵比例积分控制能使发动机出口冷却液温度振幅进一步减少16.1%,温度处于±0.5℃区间内的时间增加15.26%,但附件总能耗相比提高10.3%,提高温控精度但牺牲了附件的功耗。脉谱前馈与变论域模糊控制在温控精度与功耗优化方面整体表现最优,整车运行环境下温控精度相比模糊控制提高49.28%,同时功耗降低8.68%。

采用激光诱导荧光(laser induced fluorescence,LIF)法测量缸内直喷喷油器喷雾附壁油膜的厚度分布,研究了附壁油膜质量和平均厚度随不同的壁面温度和喷射策略的变化。结果表明:常温壁面下油膜呈"波浪状",热壁面下油膜的边缘轮廓呈"带状"凸起,在壁面温度为413K时,还出现了聚集的小液滴。保持总喷油量不变,随着壁面温度的增大,单次喷射的附壁油膜质量逐渐减小,二次喷射的附壁油膜质量先减小后增大,单/二次喷射的附壁油膜平均厚度都逐渐增大;相对于单次喷射,相同热壁面温度下的二次喷射附壁油膜平均厚度都较小,在壁面温度同为413K时最多减小了42%。仅增加第二次喷射的喷油脉宽,壁面温度为298K和373K时的附壁油膜质量先增大后减小,壁面温度为413K时附壁油膜质量逐渐增大;相同喷油脉宽下,壁面温度为413K时附壁油膜平均厚度最大,而壁面温度为298K和373K时附壁油膜平均厚度与喷油间隔相关。 The laser induced fluorescence(LIF) technique was used to investigate the thickness distribution of the fuel film of gasoline direct injection spray, and the variation of fuel film mass and mean fuel film thickness with different injection strategies and at different surface temperatures were studied. The results showed that fuel film at normal surface temperature was “wave-like”, while the edge of fuel film at the heated surface temperature was “stripe-like” and there were also some small droplets gathering at 413K. Keeping the total fuel injection amount constant, with the increase of the surface temperature, the fuel film mass of single injection decreased gradually, and that of two-stage injection decreased first and then increased, but the mean fuel film thickness became great with either single or two-stage injection strategy. Compared with the single injection, the mean fuel film thickness in the two-stage injection was smaller at the same heated surface temperature, and the maximum reduction was 42% at the same surface temperature of 413K. Just changing the second injection duration, with the increase of the second injection duration, the fuel film mass increased first and then decreased when the surface temperature was 298K and 373K, and the fuel film mass at the surface temperature of 413K increased gradually. Just changing the second injection duration and keeping the same second injection duration at different surface temperatures, the mean fuel film thickness at the surface temperature of 413K was the largest at each injection interval, and the mean fuel film thicknesses at the surface temperatures of 298K and 373K were subject to the injection interval.

使用定容燃烧弹模拟一款重型柴油机在海拔0m、3 000m和4 500m条件下运行时缸内的热力学状态,利用多种成像技术实现了撞壁燃烧过程的可视化,研究了不同海拔对撞壁喷雾燃烧的高温着火、火焰传播和碳烟生成特性的影响。结果表明,海拔从0m升高到4 500m,撞壁着火延迟从0.55ms延长到0.88ms,撞壁着火距离从20.38mm增大到26.87mm,高海拔对撞壁着火过程有明显的抑制效果;撞壁火焰呈现圆盘状火焰形态,火焰发展进入稳定阶段后,由于前锋区域的涡流强度增大,撞壁火焰铺展高度、撞壁火焰铺展宽度和撞壁火焰面积都随海拔升高而增大,但在火焰发展初期,由于撞壁平板的冷却作用,撞壁火焰尺寸在海拔升高到4 500m时减小;空间积分火焰亮度和时间积分火焰亮度均随海拔升高而增大,海拔升高到4 500m时碳烟生成速率和氧化速率均增大。 A constant-volume combustion bomb was used to simulate the thermodynamic states of a heavy-duty diesel engine when operating at altitudes of 0m, 3000m and 4500m, respectively. Based on the use of multiple imaging technologies to visualize the spray wall impingement combustion process, the effect of different altitudes on high temperature ignition, flame propagation, and soot formation characteristics of spray wall impingement combustion were studied. Results showed that as altitude increased from 0m to 4500m, the ignition delay during the spray wall impingements extended from 0.55ms to 0.88ms, and the ignition distance increased from 20.38mm to 26.87mm, indicating that high altitude had a significant suppression effect on ignition process. At this time, the burning flame assumed a disk-like shape. When the flame development entered a quasi-steady stage, the height, width and area of flame expansion rose with altitudes due to the increase of vortex intensity in flame front area. However, at the early stage of flame development, the flame size began to decrease after altitude reaches 4500m due to the cooling effect of spray impinged surface. In addition, the space-integrated flame luminosity and time-integrated luminosity rose with increased altitude, and both of soot formation and oxidation rate would increase accordingly when altitude rises to 4500m.

采用流体仿真软件CONVERGE开展了基于双直喷策略的低负荷工况下二代生物柴油/汽油活性控制压燃(reactivity controlled compression ignition,RCCI)燃烧模式的数值模拟研究,对比了常规进气道喷射汽油RCCI和双直喷RCCI的燃烧特性,并探讨了双燃料喷射时刻对双直喷RCCI燃烧的影响。结果表明:相比常规进气道喷射汽油RCCI,双直喷RCCI能够有效控制缸内汽油混合气分布,改善不完全燃烧现象;随着汽油直喷时刻的推迟,分层燃烧减弱,燃烧持续期缩短,燃烧效率降低,热效率先减小再增大后又减小,NO_x排放减少而碳烟排放增加;随着二代生物柴油喷射时刻的推迟,分层燃烧加剧,燃烧持续期延长,燃烧效率升高,热效率先增大而后减小,NO_x排放增加而碳烟排放减少。 Numerical simulation of second generation biodiesel/gasoline reactivity controlled compression ignition(RCCI) combustion mode with dual-direct injection strategy at low loads was carried out based on the fluid simulation software CONVERGE. The combustion characteristics of RCCI with dual-direct injection and RCCI with conventional intake port injection were compared, and the effect of dual fuel injection timings on combustion was discussed. The results show that compared with the conventional intake port gasoline injection RCCI, the dual-direct injection RCCI can effectively control the distribution of in-cylinder gasoline mixture and reduceincomplete combustion. With the delay of start of injection(SOI) of gasoline, stratified combustion weakens, combustion duration shortens, combustion efficiency is reduced, indicated thermal efficiency declines first and then increases and finally decreases again, NOx emissions is reduced and soot emissions increases. With the delay of SOI of the second generation biodiesel, stratified combustion intensifies, combustion duration is prolonged, combustion efficiency increases, indicated thermal efficiency increases first and then decreases, NOx emissions rise and soot emissions fall.

针对大缸径低速二冲程船用柴油机,废气再循环(EGR)技术满足TierⅢ排放时造成的油耗恶化问题,采用三维数值模拟手段,研究了EGR氛围下多次喷射与燃油喷射角度对发动机油气混合、燃烧及排放的影响。结果表明,采用30%EGR率可满足TierⅢ排放标准;喷油角度直接决定缸内混合气形成过程,喷油角度过小会导致气缸中心油束重叠形成浓混合气区,缸内空气无法充分利用;喷油角过大会导致喷雾油束和火焰撞壁,缸壁散热损失增加;而适中的喷油角度(20°)有利于提升功率,降低油耗。在EGR氛围下通过协同优化多次喷射与喷油角度,采用30%EGR率结合10.0%预喷量,主预喷间隔为15°,喷油角20°,可使NO_x排放降低65.5%,油耗仅增加1.24%;采用三次喷射可进一步改善油耗与NO_x排放之间的折衷关系,但优化潜力有限。 To address the issue of a large two-stroke marine diesel engine having higher fuel consumption due to adopting the exhaust gas recirculation (EGR) to meet the Tier Ⅲ emissions regulations, the influence of split injection and injection angle on the fuel-air mixture, combustion and emissions were studied by using three dimensional numerical simulation based on the single cylinder model of such engine with multiple injectors. The results show that 30% of EGR rate can meet Tier Ⅲ, and the injection angle directly determines the formation of fuel-air mixture in the cylinder. If the injection angle is too small, the tips of fuel sprays of the injectors overlaps in the central cylinder and forms local rich region, leading to insufficient utilization of the in-cylinder air. If the injection angle is overlarge, fuel sprays and flames collids on the cylinder wall and hence results in increased heat loss through the wall. With a moderate fuel injection angle of 20°, in contrast, optimal mixing and heat release can be achieved with improved power output and reduced fuel consumption. In the presence of EGR, synergistically optimizing split injection and injection angle can reduce NOx by 65.5% with fuel consumption increasing only by 1.24% when using 30% of EGR rate, 10.0% of fuel fraction in pilot injection, 15° of interval between pilot and main injections and 20° of injection angle. Adopting three-time injection can effectively improve the compromise between fuel consumption and NOx emissions, but with a small room for a further optimization.

以正丁醇作为助溶剂,形成柴油-甲醇-正丁醇混合燃料,并将混合燃料在单缸四冲程柴油机上进行试验研究,探究混合燃料对柴油机排放特性的影响。试验所用的混合燃料中醇类的体积比为5.09%、9.82%、14.66%和19.35%,其中甲醇在混合燃料中所占体积比为2.51%、5.01%、7.53%和10.08%,正丁醇在混合燃料中所占体积比为2.67%、4.81%、7.13%和9.27%。研究表明:燃用混合燃料柴油机有效燃油消耗率、热效率分别增加0.18%～4.08%和0.28%～3.54%;输出功率、输出转矩分别下降0.75%～11.37%和1.42%～25.03%;CO、NO、NOx等常规气体排放、PM2.5排放分别下降2.76%～45.15%、3.55%～29.21%和3.55%～20.03%;但柴油中添加醇类燃料会导致甲醛、乙醛及挥发性有机化合物等非常规排放分别上升2.78%～60.53%、5.15%～63.81%和3.75%～45.49%;柴油机燃用混合燃料PM2.5排放降低7.09%～48.94%。综上所述,柴油机燃用柴. The effect of diesel/methanol/n-butanol blend fuels on emission performance was studied with a single-cylinder 4-stroke diesel engine. The volume ratio of alcohol in the blend fuels was 5.09%, 9.82%, 14.66%, and 19.35%, and the volume ratio of n butanol was 2.67%, 4.81%, 7.13% and 9.27%, respectively. The results of the experiments indicate that the use of blend fuels will improve the fuel consumption and thermal efficiency by 0.18% to 4.08% and 0.28% to 3.54% coupled to the reduction of output power and torque by 0.75% to 11.37% and 1.42% to 25.03% and hence CO, NO, NOx and PM2.5 emissions by 2.76% to 45.15%, 3.55% to 29.21%, 3.55% to 20.03% and 7.09% to 48.94%, but the addition of alcohol fuels to diesel will cause formaldehyde, acetaldehyde and volatile organic compounds to increase by 2.78% to 60.53%, 5.15% to 63.81% and 3.75% to 45.49%, respectively. In summary, use of blend fuels of diesel and alcohol allows to mitigate PM2.5 emissions while reducing NOx emissions.