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.

针对某国Ⅵ天然气发动机各缸燃烧一致性差异过大的问题,利用计算流体力学(CFD)软件STAR-CCM+对该发动机的进气管路开展废气再循环(exhaust gas recirculation,EGR)率均匀性分析,发现第1缸～第3缸的EGR率高于第4缸～第6缸,1 200r/min全负荷工况EGR率相对偏差为-29.9%～34.2%。分析表明,EGR的引出方式为第1缸～第3缸单侧取气,导致EGR进气入口存在较大波动,是造成各缸EGR率分配不均的主要原因。从降低管路内EGR废气波动的角度提出了两种进气管路优化方案,使EGR废气在进入稳压腔之前得到了充分混合,各缸EGR率均匀性得到明显提高,EGR率相对偏差在±5%以内。 In order to solve the issue of excessive difference in combustion consistence among the cylinders of a China Ⅵ natural gas engine, an analysis of the exhaust gas recirculation(EGR) rate uniformity of the intake system was carried out by a computational fluid dynamics(CFD) software called STAR-CCM+. It was found that the EGR rates of from No.1 to No.3 cylinders were larger than those of from No.4 to No.6 cylinders, and the relative deviation of EGR rate at 1200r/min with full load was from -29.9% to 34.2%. The analysis showed that there was a large fluctuation at the EGR inlet due to EGR being extracted only from No.1 to No.3 cylinders, which mainly caused the uneven distribution of EGR rate among the cylinders. Two optimizations of intake pipe were put forward to reduce the fluctuation of EGR in the intake pipe. By using the two kinds of optimized intake pipe, the recirculated exhaust is fully mixed before entering the intake manifold, which improves the uniformity of EGR rate in each cylinder obviously and brings the relative deviation of EGR rate to within ±5%.

为研究不同海拔下柴油机颗粒过滤器(diesel particulate filter,DPF)碳烟加载规律及再生特性,在一台高压共轨柴油机上分别在两种大气压力(80kPa和100kPa)下进行了试验研究。研究内容包括全球统一瞬态循环(world harmonized transient cycle,WHTC)排放测试、DPF碳烟加载及压降特性、DPF再生过程温度场及压降特性。结果表明:高原环境下DPF的排气温度和各项排放数据指标均高于平原环境。高原环境下压降损失随碳烟的累积呈现出先快速增加后缓慢增加的趋势。再生温度和海拔高度对DPF再生压降、载体再生峰值温度、载体再生径向和轴向温度梯度、再生时机均有影响;再生温度越高及海拔越低,DPF再生压降越高;再生温度及海拔越高,再生时载体的峰值温度越高且载体径向和轴向温度梯度越大。 In order to study the soot loading law and regeneration characteristics of diesel particulate filter(DPF) at different altitudes, experimental researches were conducted on a high pressure common rail diesel engine at two atmospheric pressures of 80kPa and 100kPa, including the world harmonized transient cycle(WHTC) emissions, DPF soot loading and pressure drop characteristics, and the temperature field and pressure drop characteristics in DPF regeneration. The results show that the DPF exhaust temperature and emissions data in plateau environment are higher than those in plain environment, and the exhaust flow and oxygen concentration are higher in plain environment than those in plateau environment. The pressure drop loss at high altitude increases rapidly at first and then slowly with the accumulation of soot. The regeneration temperature and altitude have influence on the DPF regeneration pressure drop, peak temperature of the carrier regeneration, radial and axial temperature gradients of the carrier regeneration and the regeneration time. The higher the regeneration temperature and the lower the altitude, the higher the DPF pressure drop; the higher the regeneration temperature and altitude, the higher the peak temperature of the carrier regeneration, and the larger the radial and axial temperature gradient of the carrier regeneration; the higher the regeneration temperature and the lower the altitude, the higher the DPF pressure drop when the regeneration takes place.

基于一台改装后的压缩比为17的压燃式单缸发动机,展开不同喷油压力对汽油压燃燃烧模式发动机燃烧特性、爆震特性、效率特性和排放特性的研究,结果表明随着喷油压力的增加,缸内混合气形成速度加快,混合气着火时刻提前,燃烧持续期缩短,热效率呈现出先增大后略微降低的趋势。喷油压力的增加使得发动机爆震趋势增强,为降低最大压力升高率和爆震强度,采用推迟喷油策略,但高喷油压力下缸内燃烧对喷油时刻变得敏感,易产生较大的平均指示压力循环波动或爆震,燃烧控制难度增加。对不同喷油压力下爆震循环的缸压信号进行分析得出喷油压力对爆震频率无明显影响。喷油压力升高会使得未燃碳氢和CO排放降低,但同时也会使得NO_x排放增加。 An experiment of how fuel injection pressure affects the performances of gasoline compression ignition(GCI) was conducted, including the characteristics of combustion, engine knock, thermal efficiency and emissions. It was conducted on a modified single-cylinder engine with the compression ratio of 17. The results show that with the increase in the injection pressure, the air-fuel mixture forms much more quickly, the auto-ignition timing advances towards the top dead center, and the combustion duration becomes shorter. All of those lead to a higher thermal efficiency at first and a slightly lower one later. However, high injection pressure will lead to multipoint auto-ignition, causing higher maximum pressure rise rate and severe engine knock, which requires a delayed injection timing. The combustion becomes more sensitive to injection timing as the injection pressure rises, and the higher variation in coefficient of cyclic indicates mean effective pressure or knock is more likely to appear, resulting in more difficulty in combustion control. Through data analysis, no significant effects of the injection pressure on knocking frequency is found. Besides, increased injection pressure will reduce HC and CO emissions, but result in a certain increase in NOx emissions.

针对农用柴油机在瞬态突加负载工况下因涡轮迟滞效应造成的发动机转速下降和油耗上升问题,提出一种基于负载转矩主动观测的农用柴油机瞬态过程控制算法。首先,建立了农耕机耕地阻力矩和发动机驱动转矩预测模型,采用跟踪-微分器实现了作业模式识别、耕深预测及负载转矩预测,设计了增压压力前馈控制器;然后将预测模型的偏差与外部转矩干扰统一视为"总扰动",采用扩张状态观测器进行在线估计和补偿;接着基于耕深与发动机转速的动态过程信息,采用递推优化算法设计了负载转矩模型的参数学习算法,用于在线优化模型参数,提高前馈精度,降低总扰动观测负担。在试验校准的高精度Simulink平台上,对算法进行仿真验证,结果表明:较传统控制方法,采用该控制方案后,瞬态过程的空气供给速度提升53.1%,指示转矩响应速度提升44.7%,进而使发动机的转速波动降低98.8%,瞬态过程有效燃油消耗率降低7.0%。 In view of the problems of reduced speed and increased fuel consumption under transient sudden load conditions due to turbo lag effect, a transient control algorithm for an agricultural diesel engine based on load torque active observation was proposed. First of all, a prediction model of agricultural machine arable land resistance and engine brake torque was established. By adopting a tracking differentiator to implement the operation mode recognition, as well as the prediction of plough depth and load torque, a boost pressure feedforward controller was designed. Secondly, under the premise that the deviation of the prediction model and the external torque disturbance were regarded as “total disturbance”, an expanded state observer was used for online estimation and compensation. Then, based on the dynamic information of plough depth and engine speed, a parameter self-learning scheme for the load torque model was designed using a recursive optimization algorithm to improve feedforward accuracy, and reduce the observation burden of total disturbance. Finally, the algorithm was verified on a calibrated high-precision SIMULINK simulation platform. Results show that compared with traditional control method, this algorithm can increase the transient air supply speed by 53.1%, and accelerate the indicated torque response by 44.7%, thus reducing the engine speed fluctuation by 98.8%, and the transient fuel consumption by 7.0%.

为研究船用低速柴油机增压器压气机气动噪声,采用计算流体动力学和声学有限元的混合计算方法进行了数值预测。通过试验对压气机计算模型进行了验证。在3个工况下对压气机非定常流场进行了计算,其中压力脉动被用作声学计算中的声源信息;采用声学有限元方法对压气机气动噪声进行了预测。结果表明:计算流体力学和声学有限元的混合计算方法具有较高的计算精度,可以用于压气机气动噪声数值预测;压气机进口气动噪声主要谱成分为离散单音噪声和宽频噪声;离散单音噪声在叶片通过频率处有明显的指向性,存在两个突出峰值。 In order to study the aerodynamic noise of a marine low-speed diesel turbocharger compressor, a hybrid calculation method of the computational fluid dynamics(CFD) and acoustic finite element method(FEM) was used to predict it, and verified by bench test. The unsteady flow field in the compressor was calculated under three different operating conditions, where the pressure fluctuation was used as a noise source in the acoustic simulation. Results indicate that the hybrid calculation method has a higher calculation accuracy and can be used for numerical prediction of the compressor's aerodynamic noise. Moreover, the main components of aerodynamic noise at the compressor inlet include discrete tonal noise and broadband noise. As observed, the discrete tonal noise exhibits an obvious acoustic directivity at blade passing frequency(BPF) and has two prominent peaks.

针对一台低压喷射二冲程天然气/柴油双燃料发动机进行三维全尺寸模拟，研究了扫气口角度对天然气混合过程以及功率和排放的影响．结果表明：引燃油喷射前，天然气分布呈现出分层，其中扫气口角度θ＜20°时，天然气集中分布在活塞顶附近，呈“上下”分层；扫气口角度θ≥20°时，混合气浓区集中分布在气缸壁附近，呈“左右”分层，同时会出现天然气逃逸现象；适中的扫气口角度(θ＝25°)有利于降低天然气消耗率，低于此值时预燃室附近天然气稀薄，火焰传播速度低，燃烧持续期长；高于此值时，燃烧相位前移，压缩负功增加．此外，当扫气口角度过小时，由于活塞顶部天然气过浓，会使NOx排放急剧增加，甚至超过Tier Ⅲ排放法规的限值．

通过内燃机高原环境模拟试验台，研究了不同海拔条件下高压共轨柴油机在最大转矩转速点(1 500 r/min)全负荷(2 300 N·m)和部分负荷(500 N·m)工况下喷油提前角、共轨压力及循环喷油量(全负荷)对柴油机燃烧特性与性能的影响规律．结果表明：全负荷工况下，随着喷油提前角增加，柴油机滞燃期增加，最高燃烧压力和最大压力升高率增大，增大趋势随海拔增加而降低，柴油机转矩在0 km 和3 km 海拔先增加后减小，在5 km 海拔时逐步增加．随着共轨压力增加，柴油机燃烧相位提前，最高燃烧压力、最大压力升高率和转矩均增加，排温降低；部分负荷工况下，有效燃油消耗率随共轨压力增加而降低．随循环喷油量增加，转矩、排温和缸内压力均逐渐增大，最大压力升高率在3 km 海拔范围内逐渐增加、在5 km 海拔时逐渐减小．海拔每升高1 km，柴油机在全负荷工况下，最佳循环喷油量平均降低5.81%，最佳喷油提前角和共轨压力在全负荷和部分负荷工况下平均分别增加了1.2°CA、0.8°CA和4MPa、3MPa．

在一台轻型光学发动机上对比了部分预混压燃(PPC)和燃料活性控制压燃(RCCI)两种燃烧模式的着火及燃烧发展过程，并分别探究了不同喷射策略对两种燃烧方式的影响．研究发现，对于PPC 燃烧模式，混合气浓度分层越小，燃烧过程中自燃占比越高；混合气浓度分层越大，燃烧过程中火焰传播占比越高．对于RCCI 燃烧模式，缸内直喷高活性燃料比例较高时，燃烧是从高活性区到低活性区分阶段顺序自燃；缸内直喷高活性燃料比例较低时，燃烧是火焰传播与自燃共同主导的过程．从而阐明了PPC 和RCCI 相较于均质压燃(HCCI)能够实现更高负荷高效清洁燃烧的本质是，燃烧发展历程从单纯的多点自燃燃烧转变为火焰传播与自燃共存．