中文摘要:       基于计算流体力学（CFD）软件CONVERGE建立了大型低速2冲程柴油引燃缸内直喷天然气船用发动机燃烧仿真模型。首先通过试验结果对模型进行了验证，进而开展了天然气高压喷射模式（high pressure direct injection，HPDI）下米勒循环和天然气两次喷射策略对发动机压力振荡的抑制效果研究。结果表明，推迟排气门关闭时刻，整体燃烧压力降低，燃烧相位推迟，发生剧烈压力振荡的时刻也推迟。排气门关闭时刻推迟较小时压力振荡强度降低，但过度推迟反而提高缸内压力振荡的强度，这主要是缸内热力学状态变化和燃料自燃特性相互作用的结果。通过调整预喷射量，可以降低燃烧前形成的可燃混合气量，从而影响燃烧过程中预混合燃烧比例，可以有效抑制压力振荡.但会导致输出功率降低及能耗增大。相比预喷射量，喷射间隔对缸内压力振荡的影响较小，但过大喷射间隔会影响燃烧相位，导致功率损失严重。合理的喷射策略可以在抑制压力振荡的同时保证功率输出。 英文摘要:       Based on the computational fluid dynamics(CFD) software(CONVERGE), the simulation model of a large low-speed two-stroke marine engine in which pilot diesel and natural gas are injected directly in cylinder was established. Validated by the experimental data from the literature, the model was then applied to studying the suppression effect of the Miller cycle and natural gas two-stage injection strategy on the pressure oscillation in high pressure direct injection mode. The calculation results indicated that when the exhaust valve was closed later, the overall combustion pressure was lower, both the combustion phase and the moment of severe pressure oscillation were delayed. The intensity of pressure oscillation was reduced with smaller delay of exhaust valve closing, while it was increased instead with an excessive delay. This was primarily attributed to the competitive relation between in-cylinder thermodynamic state and auto-ignition characteristics of fuel. Adjusting the pre-injection quantity of natural gas would reduce the formation of premixed combustible mixture before combustion, thus reducing the proportion of premixed combustion in the combustion phase, which could effectively suppress pressure oscillation, but could also reduce the output power and increase the fuel consumption. Compared with the pre-injection quantity, varying injection interval has less effect on the pressure oscillation, but the excessive injection interval would affect the combustion phase, resulting in considerable power loss. A reasonable injection strategy can ensure the power output while suppressing intense pressure oscillation.

中文摘要:       基于CONVERGE建立了高压直喷（high pressure direct injection, HPDI）天然气低速船机三维仿真模型,并基于该模型研究了米勒循环和废气再循环（exhaust gas recirculation, EGR）对发动机燃烧特性及污染物排放的影响规律,探究了米勒循环耦合EGR路线满足Tier Ⅲ排放法规的可行性。研究结果表明,单独使用30%EGR率可满足Tier Ⅲ排放标准,但指示油耗和碳烟排放增加显著；应用米勒循环降低NOx 排放的潜力低于EGR；过大的排气门晚关角度会增大压气机工作负荷,且降低等量NOx 排放情况下油耗牺牲较大；采用25%EGR率耦合小程度米勒循环（排气门关闭时刻推迟5°曲轴转角）并适当提前天然气喷射正时（提前2°曲轴转角）,可在指示油耗仅增加158%的前提下降低77%的NOx 排放,是满足Tier Ⅲ排放法规可行的技术路线。 英文摘要:       Based on a three-dimensional simulation model established using CONVERGE, the effects of exhaust gas recirculation and the Miller cycle on the combustion characteristics and emissions were studied to explore the feasibility of the Miller cycle coupled with EGR to meet Tier Ⅲ emission regulations for low-speed high-pressure direct injection natural gas marine engines. The results show that using 30% of EGR rate alone can meet Tier Ⅲ emission standards, but with a significant increase in the indicated fuel consumption and soot emissions; the Miller cycle is not as effective as EGR in the potential to reduce NOx emissions; excessive exhaust valve closing delay will cause increase in compressor workload, and lead to a considerable increase in fuel consumption when the same amount of NOx emissions is reduced. Coupling mild Miller cycle(delaying exhaust valve closing by 5° in crank angle) with 25% of EGR rate and the proper natural gas injection timing(advancing 2° in crank angle) can reduce NOx emissions by 77% with only a slight increase in the fuel consumption by 1.58%, which is a feasible way to meet Tier Ⅲ emission regulations.

中文摘要:       利用CONVERGE仿真平台建立点燃式液压自由活塞发动机（hydraulic free piston engine, HFPE）三维仿真模型,并实时求解作用在活塞顶表面的压力,从而使缸内燃烧气体力和液压力耦合。在此基础上研究了增压多点点火HFPE的指示热效率情况。研究结果表明：采用多点点火能改善增压HFPE的指示热效率。采用多点点火之后,最佳指示热效率对应的压缩比变小。多点点火使增压比较大时的工况也呈现较高的指示热效率。采用多点点火后,高效区能够扩大到增压比为4以上。适当增加活塞组质量能够延长活塞在上止点附近停留时间,从而进一步提高指示热效率。 英文摘要:       A three-dimensional simulation model of an ignited hydraulic free piston engine(HFPE) was established by using a CONVERGE simulation platform. The pressure acting on the top surface of piston was solved in real time to promote the coupling of the combustion gas force in the cylinder with the hydraulic pressure. On this basis, the indicated thermal efficiency and knocking conditions of the pressurized multi-point ignition HFPE were also studied. Results show that the use of multi-point ignition improves the indicated thermal efficiency of the pressurized HFPE, which results in a smaller compression ratio for the best indicated thermal efficiency and a higher indicated thermal efficiency at a higher boost ratio. Use of multi-point ignition also expands the boost ratio in the high efficiency zone to over 4. Moreover, an appropriate increase in the mass of piston assembly can extend the residence time of the piston near the top dead center, thus further improving the indicated thermal efficiency.

中文摘要:       为进一步提高发动机热效率，提出高滚流Atkinson循环燃烧系统概念。其特征是采用高滚流气道和活塞组合，配合Atkinson循环和废气再循环（EGR）技术，提高缸内的滚流和湍流水平，加快燃烧速度，同时降低汽油机爆震倾向。利用GT-Power和AVL-FIRE软件针对某型汽油机进行了一维整机工作过程和三维计算流体动力学（CFD）模拟分析。结果表明：高滚流气道有利于促进缸内滚流运动，滚流比由原机的0.5提高到2.6；配合高滚流活塞后，使进气过程中产生的缸内初始滚流和压缩过程中的滚流维持作用都比原机有所增强，湍动能水平提升6.3%，瞬时放热率与原机相比平均提高15%；在此基础上，采用进气门晚关的方式实现Atkinson循环，并增加EGR系统，降低高压缩比带来的爆震倾向，比油耗在整个万有特性中均呈下降趋势，最低比油耗区明显变大，最低比油耗相比原机下降11.3 g/(kW·h)。 英文摘要:       For the improvement of engine thermal efficiency, the concept of the Atkinson cycle with high tumble combustion system was proposed, which adopts the combination of high tumble intake port and piston, and coordinates the Atkinson cycle and exhaust gas recirculation(EGR) technology to improve in-cylinder tumble and turbulence level, accelerate combustion speed, and reduce knock tendency. The engine work process model and in-cylinder computational fluid dynamics(CFD) model of a certain engine were set up by the GT-Power and AVL-FIRE software respectively. The simulation results show that a high tumble intake port benefits in-cylinder tumble, which increases from 0.5 of the base engine to 2.6; with high tumble intake ports and pistons, both the initial tumble generated during the intake process and the tumble maintained during the compression process are stronger than the base engine, the average turbulence energy increases by 6.3%, and the average heat release rate increases by 15% compared with the base engine. In order to decrease the knock tendency caused by high compression ratio, the Atkinson cycle, which is realized by late intake valve closing timing, was introduced with EGR based on the foresaid high tumble. The results show that the brake specific fuel consumption(BSFC) in the universal characteristic appears downward trend. The lowest BSFC area becomes larger obviously, and the lowest BSFC decreases by 11.3 g/(kW·h) against the base engine.

中文摘要:       针对某型号天然气/柴油双燃料发动机，在其连杆的设计和开发过程中，运用ABAQUS和FEMFAT软件对连杆进行CAE分析，原设计连杆接触分析显示接触开度不满足安全要求。为此对连杆进行优化设计，优化后的连杆CAE分析表明：连杆杆身与大端接触面采用弧形设计能有效解决连杆接触开度问题，且优化后的连杆变形、接触应力及高周疲劳（high cycle fatigue, HCF）强度都在许用范围之内，满足设计安全需要。这一结论可为提高双燃料发动机的设计安全性提供有效的科学方法和可靠的理论依据，并为后续连杆装机验证提供有力的理论支撑。 英文摘要:       CAE analysis and optimization design of the safety of connecting rod contact opening were carried out by using the ABAQUS and FEMFAT software. Results show that the arc-shaped design of the bottom of the connecting rod shank can effectively solve the unsafe problem of the connecting rod contact opening, and the optimized connecting rod deformation, contact stress and high-cycle fatigue strength are within the allowable range, thus meeting the requirements of safety design. This conclusion can provide an effective scientific method and reliable theoretical basis for improving the safety of dual fuel engines, and create good conditions for the installation test of connecting rods in the future.

2019年第6期目次

通过一台直列 4 缸汽油机分析了喷油模式对直喷汽油(GDI)发动机冷起动过程及冷态怠速过程的影响．结果表明：通过调整喷油策略可以改变缸内混合气的燃烧过程，在二次喷油比例为 0.6∶0.4、喷油定时分别为上止点前 300° CA 和 140° CA、环境温度为-30 ℃条件下，发动机的燃烧特性最佳，HC 排放最低．在车辆冷起动过程中，通过二次喷射可以有效缩短混合气的滞燃期和燃烧持续期，以达到缩短起动时间、提高起动性能的目的．在起动后的怠速阶段，采用二次喷射可以大幅提高发动机的燃烧稳定性，有效消除怠速不稳的问题．在闭环控制阶段，通过二次喷射合理组织缸内混合气分布，可以有效改善减稀混合气造成的车辆抖动问题．此外，缸内混合气燃烧过程的优化可以有效降低冷起动过程的 HC 和 CO 排放，但会造成 NOx 排放的小幅升高．

通过一台耦合了外置燃料重整器的单缸发动机，系统研究了温度对 PRF90 燃料低温重整产物及发动机燃烧特性的影响，并结合 Chemkin 软件进行了相关化学动力学计算和分析．结果表明：随着重整温度升高，重整混合气中甲醛、CO 和 CO2 增多，重整混合气活性下降；PRF90 燃料的重整产物导入到发动机中，燃烧相位改变；当重整温度＜650 K 时，燃烧相位随着重整温度的升高而提前，而当重整温度＞650 K 时，发动机发生失火现象；重整气的导入对发动机的燃烧稳定性影响有限；合理控制外置燃料重整器重整边界条件，可在降低有害排放的同时改善发动机的指示热效率(2%)．

通过一台 Yamaha YBR250 发动机原机，进行乙醇直喷(EDI)与汽油进气道喷射(GPI)的改装，研究了 EDI喷油时刻对发动机缸内混合气形成、燃烧和排放的影响，同时建立了 EDI 结合 GPI 发动机的三维计算模型，对试验工况进行了数值模拟．分别对喷雾模型和燃烧模型进行了试验标定，结果表明：通过改变 EDI 喷油时刻，进气涡流与喷雾带动气流的运动共同作用于缸内燃料的蒸发雾化，可以在火花塞附近形成不同程度的燃料浓区；延迟EDI 喷油时刻至 100° CA BTDC，能够有效地协同壁面传热以及乙醇蒸发作用，降低点火时刻缸内温度，从而降低最大爆发压力和缸内燃烧温度；相对于早喷工况，EDI 喷油时刻为 100° CA BTDC 的工况能够有效降低缸内 HC及 NO 排放．

基于 GT-Power 建立带柴油机颗粒捕集器(DPF)的增压柴油机一维仿真模型，研究了 DPF 在不同海拔下对增压柴油机动力性、经济性及排放特性的影响，同时研究了不同海拔下 DPF 的工作特性，并采用 3 种不同型式的载体进行了仿真对比．结果表明：高原环境对增压柴油机低转速工况性能影响较小；高原环境下，增压柴油机中、高转速的动力性、经济性下降明显；中、高转速工况下，随着海拔升高，增压柴油机碳烟和 CO 排放均增加，NOx 排放降低；不同海拔下，DPF 对增压柴油机动力性、经济性影响较小，海拔为 0km 与 4km 条件下 DPF对增压柴油机原始排放均影响较大；DPF 压降随海拔上升而增加，高原环境对低转速工况下 DPF 捕集效率影响较小，中、高转速工况下，DPF 捕集效率随海拔上升而增加；不同型式载体的 DPF 工作特性随海拔变化的表现具有一致性，高目数和非对称结构载体有利于降低 DPF 压降和增大载体容灰量．