针对某型柴油机功率提升后主轴承润滑性能恶化的现象，考虑轴颈与轴瓦表面粗糙度、曲轴与轴承座弹性变形的影响，建立了12 V90°柴油机主轴承的润滑分析计算模型．根据弹性流体动力润滑、轴承动力学及平衡率计算理论，分析了不同曲轴平衡率对主轴承的润滑性能的影响．采用正交试验研究了平衡率、轴承宽度及轴承间隙对最小油膜厚度、最大油膜压力、平均摩擦损失功和峰值粗糙接触压力的影响，并提出了改进方案．结果表明：曲轴平衡率对主轴承润滑性能有很大的影响，对最小油膜厚度、最大油膜压力和峰值粗糙接触压力的影响权重与轴承间隙相接近，均低于轴承宽度；平衡率对平均摩擦损失功的影响权重最大；相比轴承宽度、轴承间隙等影响因素，曲轴平衡率在强化柴油机主轴承润滑设计阶段也应重点考虑．

蜗壳固有的非轴对称结构使蜗壳出口流动周向存在很大的不均匀性，会对下游部件内的流动产生不利影响，使喷嘴环、叶轮流场中均存在非轴对称流动现象．基于某可调向心涡轮非轴对称流场结构的分析，提出了采用非均匀布置导流叶片和优化喷嘴座连接臂结构的设计方案来改善涡轮流场的非轴对称流动．给出了非均匀布置导流叶片的优化目标和优化流程，以及喷嘴座连接臂的改型设计方案．通过改型前、后的涡轮性能试验，验证设计方案的有效性．结果表明：在不同导流叶片开度、不同相似转速情况下，改型后的涡轮等熵效率较改型前均有所提高，大速比工况时效率提高幅度比小速比工况时更为明显；在最大导流叶片开度时，改型后的涡轮等熵效率较改型前相对提高值最大为7.53%．

中文摘要: 基于定容燃烧弹与超高速数码相机搭建的LED-Mie散射喷雾试验台，研究了不同参数对柴油、汽油质量占比20％的柴汽混合油（记为G20）单段与两段喷射主喷液相喷雾特性的影响。结果表明，单段喷射喷雾贯穿距与喷雾锥角随喷射压力的增大而增大，G20喷雾贯穿距略小于柴油喷雾贯穿距，G20喷雾锥角略大于柴油喷雾锥角。将环境温度由300 K升高到850 K，喷雾贯穿距变小且喷雾很快达到稳定。冷态环境下（300 K），两段喷射主喷喷雾贯穿距起始阶段与单段喷射喷雾贯穿距基本一致，但随着喷雾发展200 μs左右后，两段喷射主喷喷雾贯穿距变得略小于单段喷射喷雾贯穿距。两段喷射主喷喷雾锥角略大于单段喷射喷雾锥角，预主喷间隔时间对喷雾锥角影响较小。 英文摘要: The LED-Mie scattering spray test bench was built based on a constant volume combustion chamber and a high-speed digital camera. The effects of different parameters on liquid spray characteristics of diesel and gasoline/diesel blend of 20% gasoline mass fraction(denoted as G20) with single injection and the main injection of split injection (the main injection) were studied. The results show that: The spray penetration length and spray cone angle of both fuels become greater with the increase of injection pressure of single injection, and the spray penetration length of the G20 is smaller than that of the diesel while the spray cone angle of the G20 is larger than that of the diesel. When the temperature rises from 300 to 850 K, the spray penetration lengths of both fuels decrease and the sprays quickly stabilize. In the cold environment (300 K), the two-fuel spray penetrations of the main injection are basically the same as those of the single injection at the first, but when both sprays develope for 200 μs, the penetration lengths of the main injection are slightly smaller than those of the single injection. The two-fuel spray cone angles of the main injection are slightly larger than those of the single injection, and the interval between pilot injection and main injection of the split injection has little effect on the spray cone angles.

中文摘要: 考虑喷射初期喷嘴压力室内部压力建立过程，推导了适用于喷射初期的液相贯穿距模型。随后在定容燃烧弹内营造柴油机上止点附近高温高压氛围条件，采用背景光散射法试验研究了喷射压力、环境温度及环境密度对蒸发喷雾液相贯穿距发展历程的影响，并将试验结果与模型进行对比。模型与试验结果表明：在喷射初期，液相贯穿距并非按照Hiroyasu模型预测的随时间t线性变化，而表现出一个加速过程，与t1.5成正比；随后由于喷雾破碎和喷嘴压力室内部建压完成，液相贯穿距与t0.75和t0.5成正比。 英文摘要: Considering the fuel pressure building process inside the nozzle sac, a model suitable for the liquid penetration at the initial stage of fuel injection was derived. Then, in the high-temperature and high-pressure environment near the top dead center of a diesel engine built in a constant volume combustion vessel, the effects of the injection pressure, ambient temperature and density on the development process of evaporating spray liquid penetration were tested by using diffused back-illumination method, and compared with the simulation calculation. Results show that at the initial stage of fuel injection, the liquid penetration does not change linearly with the time of t as predicted by Hiroyasu model, but first presents an acceleration process that varies with the time of t1.5 and then changes with the time of t0.75 and t0.5, respectively, due to the spray breakage and fuel pressure built up in the nozzle sac.

中文摘要: 基于三维计算流体动力学（CFD）软件CONVERGE,耦合甲苯掺比燃料（toluene reference fuel, TRF）简化动力学机理及多步现象学碳烟模型,建立汽油压燃（GCI）的数值模拟模型。通过改变气道喷射比例、主喷时刻和预主喷间隔研究了高负荷条件下气道喷射结合缸内直喷的喷油策略对GCI燃烧及碳烟生成过程的影响。研究结果表明,增加气道喷射比例、提前主喷时刻和增大预主喷间隔都能够缩短燃烧持续期,使放热更为集中,从而降低碳烟排放；改变气道喷射比例对碳烟成核及表面生长有较大的影响,主喷时刻提前能够提高氧化速率。当气道喷射比例为40%，主喷时刻为-8°，预主喷间隔为15°时,碳烟排放为 0.0151g/(kW·h),相比试验基准工况降低了33.8%,而最大压升率也控制在可接受的范围内。 英文摘要: Based on the three-dimensional computational fluid dynamics(CFD) software CONVERGE, a computational model of gasoline compression ignition(GCI) was established by coupling reduced toluene reference fuel(TRF) chemical kinetic mechanism with a phenomenological soot model. With various port fuel injection(PFI) ratios, main injection timings and pilot-main injection intervals of direct injection(DI), the effects of the injection strategy combining PFI with DI on the combustion and soot formation processes of GCI at high load conditions were studied. The results show that higher PFI ratio, earlier main injection timing and greater pilot-main injection interval can shorten the combustion duration and increase the concentrated combustion, resulting in less soot. Besides, the PFI ratio has a great influence on soot nucleation and surface growth, and earlier main injection timing can increase the oxidation rate. With the PFI ratio of 40%, main injection timing at 8° in crank angle before the top dead center and pilot main injection interval of 15°, the soot is 0.0151 g/(kW·h), which is 33.8% lower than the baseline experimental condition, and the maximum pressure rise rate is also controlled within an acceptable range.

中文摘要: 在一个恒定体积的密闭容器中开展了一系列圆柱形膨胀乙醇预混火焰胞状不稳定性的数值模拟研究，并通过临界贝克莱数、扰动对数增长率和临界火焰半径等理论分析研究了乙醇预混火焰胞状不稳定性。结果表明，在初始压力1 MPa、初始温度358 K、当量比0.8~1.6条件下，乙醇预混火焰胞状不稳定性非单调性增加，在当量比为1.2时不稳定性最为强烈。原因是热扩散（thermal diffusion, TD）不稳定性分子扩散影响明显，随着当量比的变化而急剧变化，当量比增加，扰动对数增长率先增大后减小；相反，流体动力学不稳定性对当量比并不敏感。此外，在当量比低于1.2时，几乎保持恒定的临界贝克莱数和急剧减小的火焰厚度导致临界火焰半径大幅下降，并在1.2处达到最小值。数值模拟和理论研究显示出一致的结果。 英文摘要: A series of numerical simulations of premixed cylindrical expanding ethanol/air flames in a constant volume were performed to investigate the cellular instability. Then a theoretical analysis in terms of critical Peclet number, logarithmic growth rate and critical flame radius was carried out to explore the flame instability. The results demonstrate that at pressure of 1 MPa and temperature of 358 K, ethanol/air flame cellular instability increases non-monotonically with the equivalence ratio changing from 0.8 to 1.6 and has the most intense instability when the equivalence ratio is 1.2. It is found that thermal-diffusion instability changes dramatically with increased equivalence ratio mainly due to molecular diffusion, and logarithm growth rate increases first and then decreases. On the contrary, hydrodynamic instability is insensitive to the equivalence ratio. Finally, the almost constant critical Peclet number and remarkably reduced flame thickness lead to a great decrease in critical flame radius when the equivalence ratio is less than 1.2, and critical flame radius reaches the minimum when the equivalence ratio is 1.2. Both numerical and theoretical investigations showed a consistent result.

中文摘要: 为提高航空煤油在点燃式发动机中的燃烧热效率，改善发动机爆震及拓宽发动机负荷范围，以3号航空煤油（RP3）为基础燃料，以乙醇为辅助燃料，基于一台单缸水冷、压缩比可调、四冲程点燃式发动机结合高压共轨缸内直喷技术，开展了不同负荷、不同乙醇和航空煤油掺混比、不同喷射压力、不同喷射时刻下航空煤油燃烧特性的试验研究。结果表明，在压缩比为7的条件下，由于爆震的限制，发动机负荷仅能达到原机的72.0%。而乙醇具有较强的抑制爆震的能力，随着乙醇在航空煤油中掺混比例的增加，发动机负荷区间不断拓展，当乙醇的掺混比为10%时发动机可实现全负荷工作。继续增大乙醇的掺混比例，可进一步提升功率并降低油耗。为探究喷油时刻对动力性、经济性的影响，试验测定了5种喷油时刻对燃烧性能的影响。当喷油时刻为压缩上止点前300°时，发动机具有较好的动力性；当喷油时刻为上止点前360°时，发动机具有较好的经济性。 英文摘要: In order to improve the thermal efficiency, detonation and operating range of spark ignition engines fueled with aviation kerosene, a single-cylinder, water-cooled, 4 stroke, variable compression ratio engine with high pressure common rail and in-cylinder direct injection was used to test the combustion characteristics of using kerosene/ethanol blend fuel under different load, ethanol/kerosene blending ratio, injection pressure and injection timing conditions. Results show that under the condition of injection pressure of 7, the engine load can only reach 72% of the original engine load due to the limitation of detonation. Ethanol has a higher ability to suppress detonation. With the increase of ethanol content in the blend fuel, the engine operating range expands continuously. When the ethanol/kerosene blending ratio is 10%, the engine can be operated at full load. On this basis, continuing increase in ethanol content can further increase engine power, and reduce fuel consumption. In order to explore the influence of fuel injection timing on engine power and fuel economy, the effect of five injection timings on combustion performance was tested. As observed, the engine has better power with an injection timing of 300° before top dead center, and higher economy with an injection timing of 360° before top dead center.

中文摘要: 设计开发了一种配备新型周向变流式排气混合器的筒式后处理系统，以某型3.0 L排量的国六柴油机后处理为例，首先设计了排气混合器结构，建立了该催化器的流动及尿素喷射、雾化和扩散模型，进行全尺寸排气流场模拟分析，研究了混合器后的速度均匀性、NH3浓度分布和压降损失等，并对特征尺寸进行了优化。结果表明，优化的结构尺寸及设计使标定工况下NH3均匀度可以达到0.996，混合器压降不超过4.17 kPa。然后进行了发动机台架试验，验证了新开发设计优化的后处理系统阻力较小，标定工况下实测的NH3均匀度高达0.98，不同空速和温度情况下，不带扰流板的混合器表现更优。最后进行了发动机排放试验，全球统一瞬态循环和全球统一稳态循环结果达到国六标准要求，确证了新开发的选择性催化还原系统及排气混合器能够用于道路车辆国六重型柴油机。 英文摘要: A drum-type aftertreatment system equipped with a new type of circumferential variable flow exhaust mixer was developed.Taking the aftertreatment of a 3.0 L China Ⅵ diesel engine as an example. First, the structure of the exhaust mixer was designed, the models of flow, as well as urea injection, atomization and diffusion in the catalytic converter were established, the full-scale exhaust flow field simulation analysis was carried out, the velocity uniformity, NH3 concentration distribution and pressure drop loss of the mixer were studied, and feature sizes were optimized. The results show that the uniformity of NH3 can reach 0.996 with the pressure drop of less than 4.17 kPa at the rated condition. Then, the validation by bench test was conducted. The results show that the newly designed aftertreatment system has smaller resistance, NH3 uniformity at the rated condition is 0.98, the mixer without spoiler performs better at different space velocities and temperatures. Finally, the engine emissions testing was carried out, the WHTC and WHSC cycle emissions meet the requirements of China Ⅵ standards, confirming that the newly developed SCR system and mixer can be used in the China Ⅵ heavy-duty diesel engine for on-road vehicles.

中文摘要: 通过搭建柴油机后处理试验台架，运用计算流体力学(CFD)对选择性催化还原系统（SCR）内的反应进行仿真计算，设计4种混合器和3种整流器方案，研究了不同混合器及整流器结构对SCR系统内NH3分布及NOx 转化效率的影响。结果表明：混合器能够有效改善SCR内NH3分布均匀度及NOx 的转化效率。综合分析，有7个厚度均为2 mm的叶片且叶片与径向方向的夹角均为30°的方案M2的混合器结构设计较优；气流受到入口扩张管的扩张作用之后，经过方案D1的整流器，使得SCR系统具有更高的NH3分布均匀度和NOx转化效率。混合器和整流器结合可以实现流场的优化，提高NOx转化效率。 英文摘要: A diesel engine aftertreatment test bench was built. A numerical simulation model of selective catalytic reduction(SCR) was established with the computational fluid dynamics(CFD) software, and the reliability of the simulation model was verified.Four mixers and three rectifier schemes were designed and their effects on NH3 distribution and NOx conversion efficiency in SCR system were studied. First the effect of different mixers on NH3 distribution and NOx conversion efficiency in the SCR system was investigated. The results show that the mixer can improve the uniformity of NH3 distribution and the conversion efficiency of NOx in the SCR catalyst, and the M2 mixer having seven blades with a thickness of 2 millimeters and an angle of 30° between the blades and their radial directions is the best. Then, the effects of combination of M2 mixer with different rectifiers on NH3 distribution and NOx conversion efficiency in SCR systems are analyzed. The results show that the combination of the mixer and rectifier can optimize the flow field and improve the NOx conversion efficiency, and D1 rectifier makes the SCR system have higher NH3 distribution uniformity and NOx conversion efficiency.

中文摘要: 对某4缸高压共轨柴油机进气道进行改造，搭建了柴油/汽油双燃料反应活性控制压燃（reactivity controlled compression ignition， RCCI）发动机专用试验台架，设计了柴油/汽油双燃料RCCI燃烧汽油喷射控制策略，实现了全工况下汽油与柴油的协调喷射控制，系统地研究了不同运行工况下，不同汽油替代率对柴油机燃烧与排放性能的影响规律。结果表明：采用柴油/汽油双燃料 RCCI燃烧控制策略，发动机可在其运行工况范围内实现高效清洁燃烧，随着汽油替代率的增加，发动机缸内最高压力逐渐增大，缸压峰值出现时刻推迟，放热率峰值降低，燃烧持续期延长，燃油消耗率降低，有效热效率升高，全碳氢、CO排放增加，NOx和碳烟排放降低。 英文摘要: 4-cylinder high pressure common rail diesel engine test bench was modified to have reactivity controlled compression ignition(RCCI) combustion. A coordination-control strategy of injection for RCCI combustion was developed to adjust gasoline and diesel injections at the whole operating conditions. The effects of different gasoline fraction on the combustion and emissions of diesel engine operated with RCCI mode at different operating conditions were studied. The results show that the diesel/gasoline RCCI combustion control strategy can achieve an efficient and clean combustion. With the increase of gasoline fraction, the peak in-cylinder pressure increases gradually and appears late, the peak heat release rate decreases, the combustion duration is prolonged, the brake specific fuel consumption(BSFC) declines, and the effective thermal efficiency becomes great. And the emissions of hydrocarbon and CO increases remarkably due to the unburned fuel at low load operating conditions. Operating with the RCCI mode, the engine has higher volatility and better overall fuel-air mixing, resulting in improved combustion and reduced nitrogen oxide(NOx) and soot emissions. A good trade-off between NOx and soot emissions is achieved perfectly.