民用大涵道比涡扇发动机吸鸟过程动态性能仿真研究

为验证民用大涵道比涡扇发动机对《航空发动机适航规定》CCAR33.76吸鸟适航条款的适用性,针对吸鸟条款中的中鸟附加完整性子条款开展数值仿真研究。基于风扇叶片鸟撞过程动力学仿真结果及鸟撞前后风扇特性数值计算结果,以某型发动机为例建立吸鸟过程动态性能仿真模型,完成了发动机从吸鸟开始到最终稳定的动态过程仿真,获得了吸鸟过程及最终稳定后的性能变化情况。结果表明:吸鸟后发动机性能急剧变化的主要因素是风扇叶片的塑性形变,通过起飞状态发动机吸鸟前后稳态节流特性对比,起飞推力下降约8%,满足持续的功率或推力损失不超过25%的条款要求;随着转速下降,风扇外涵喘振的风险极高,需改进设计保证吸鸟后风扇外涵仍具有足够的裕度;吸鸟前后,涡轮进口温度及发动机排气温度均下降,不存在超温风险。     

装备封闭式吸水罐的泵站水力学特性研究

为研究封闭式吸水罐机组运行与内部流态的关系,对四平泵站进行了CFD数值计算,对比分析了单泵、两台泵和三台泵运行时不同工况下的水力损失和内部流场的差异。结果表明,封闭式吸水罐机组的流动与开敞式进水池存在明显差异,由于吸水罐进口距离吸水罐壁面较短,使得冲击水流对机组吸水的影响较大,导致中间机组的流态较为恶劣,边机组的流态反而较好。因此,采用封闭式吸水罐形式的泵站,在单泵或两台泵运行时,可以优先考虑边机组的组合运行。     

关于吸汽剖面测试中油层吸汽量计算方法研究

在蒸汽吞吐或蒸汽驱开发方式中,为了分析稠油井注蒸汽效果,通常需要在井筒中进行吸汽剖面测试,并利用测得的数据进行油层吸汽量计算、油层动用程度等分析解释工作.为了减少人工因素、仪器操作等对测试数据可靠性的影响,通常要求按照不同的仪器下入(上提)速度做多次测试,在数据进行分析解释时,综合考虑多次测试数据.为此,对在实际工作中常年使用的油层吸汽量计算方法进行了总结,并推导出了详细的计算方法:使用盖层、隔层段获取的流量测试数据的算术平均值来计算每个油层的相对流量,同时应用多套测试数据的算术平均值来精确每个油层的吸汽量;给出了计算公式.结合200余口1注汽井的吸汽剖面测试数据,利用该方法进行了试算.结果表明,计算结果与油层的实际吸汽情况非常接近,证明该方法有效可行.     

连续悬臂梁动力吸振器的模型研究

针对吸振器动力参数固定不可变或仅能产生离散变化的局限性问题,在连续悬臂梁的基础上通过增加滑动质量块的方式,设计了一种新型的参数可连续变化的悬臂梁吸振装置,并对其进行了共振频率、效果试验分析.为提高主体振动控制的效果又对参数进行了优化分析.结果表明,该装置对受固定频率简谐激励的主体结构进行动力吸振可行有效,动力参数连续可调.     

涡轴发动机非均匀吞雨对粒子分离器性能的影响

针对航行非均匀吞雨条件对航空发动机性能的影响,研究了吞雨条件对涡轴发动机粒子分离器性能的影响规律。考虑雨滴与空气之间气动破碎的物理现象,采用欧拉-拉格朗日多相流颗粒追踪模型,分析了吞雨量、吞雨粒径及非均匀吞雨条件对粒子分离器气动性能的影响。结果表明：吞雨量为0～8%时,粒子分离器扫气比增加11.34%、总压损失系数增加0.36%、总压畸变度减小0.328%、分离效率增加4.2%;吞雨量的增大,在引起较大的总压损失的同时也带来了较大的分离效率和较小的出口流场畸变;吞雨粒径为50～500μm时,粒子分离器扫气比减小9.78%、总压损失系数减小0.09%、总压畸变度增加0.028%、分离效率增加5.27%;吞雨粒径的增大,在以粒子分离器出口流场畸变增大为代价的条件下,获得了较小的总压损失和较大的分离效率;非均匀吞雨时,粒子分离器扫气比减小0.92%、总压损失系数增加0.004%,总压畸变度增加0.054%,分离效率增加1.61%;非均匀吞雨带来了更大的总压损失和出口流场畸变,以此得到较大的分离效率。     

LNG发动机功率恢复模拟研究

应用AVL-BOOST软件建立了LNG发动机的计算模型,利用模拟计算的方法得出了LNG发动机功率损失情况,分析了功率损失的原因.然后通过优化压缩比、点火提前角等措施,使LNG发动机的功率得到恢复.功率损失由优化前的21.9%降低到6%左右.     

动力总成动力吸振器特性研究

采用合适的动力吸振器对汽车动力总成的弯曲共振有较好的抑制作用,动力总成工况复杂,吸振器选择不合理反而可能适得其反。通过对动力总成吸振器进行试验研究,分析了动力总成吸振器的温度特性和激励特性,并应用于动力吸振器设计,成功解决了某车型由于动力总成弯曲共振导致的车内振动噪声大的问题。     

燃气分析在燃气轮机中的特殊应用

本文提出燃气分析在燃气轮机中的特殊应用,包括用燃气分析法求航空发动机的喷气推力、功率、空气流量,求燃烧室出口温度,以及求非单一燃料燃烧室的燃烧效率和余气系数。试验表明,用笔者导出的公式计算结果与用常规方法实测结果比较,相差不大于6％。     

自由活塞式斯特林制冷机吸振器部件优化设计

对自由活塞式斯特林制冷机的吸振器部件进行理论仿真分析和结构优化设计。结构优化设计主要从吸振器的配重块布局、固定螺母配置、阻尼特性等3方面开展。通过调整配重块的非中心对称分布，改善吸振器部件的1、2阶模态偏差，避免吸振器部件的翻转运动对吸振性能产生影响；通过对吸振器表面喷涂阻尼材料，改善其阻尼特性，提升吸振效果。开展整机振动测试，测试结果表明优化后的整机振动幅值为优化前的1/5，优化设计效果明显。     

小功率航空活塞发动机重油技术进展

小功率航空活塞发动机是微型无人机系统的主要动力型式,单一燃料的重油使用是未来无人机动力系统发展的必然趋势。结合国内外无人机发展趋势和动力系统型式选择,分析了小功率航空重油活塞发动机的应用需求特点;根据航空燃料发展的单一化趋势,指出了小功率航空活塞发动机采用重油的发展趋势和面临的技术瓶颈;整理了现阶段国内外在小功率航空重油技术方面的不同创新思路和实现型式,分析评估了不同技术路线的应用特点和技术难度。     

On efficient utilization of fuels

Various methods are developed to conserve fuels by increasing the efficiencies of heat engines. These efforts are limited by fundamental constraints on efficiency, as specified by the Carnot engine.We consider a cyclic process during which heat is converted into work while no other body, except the atmosphere, acts as both the source and sink, and show that the possibility of constructing heat engines with 100% efficiency need not be totally ruled out. If the cycle of a heat engine partially coincides with a natural cycle, its efficiency can reach the value of 100%.Although there exist many cycles in nature, the most convenient cycle for this purpose is the cycle of rain formation. Cycles of engines converting CDE or concentration difference energy (i.e., the potential energy stored in two similar and separated solutions of unequal concentrations) into work can always be so designed that they partially coincide with the cycle of rain formation. For a practical CDE engine, the evaporation of water from dilute solution may have to be carried out rapidly by burning fuels instead of using heat from the atmosphere. While this procedure will have an adverse effect on the overall engine efficiency, the efficiency of fuel utilization may still be very high.A possible arrangement of a CDE engine utilizing a semipermeable membrane is discussed. Calculations indicate that the efficiency of fuel utilization of such an engine would be independent of temperature and would increase (theoretically indefinitely) with the solubility of the solute.     

船用低速机十字头滑块和十字头轴承摩擦动力学建模及低摩擦设计

以某型号船用低速机为对象,基于多体动力学和混合润滑耦合建模,研究了十字头滑块和十字头轴承的摩擦动力学性能。利用MEBDF算法对高度非线性和刚性的摩擦动力学方程组进行了求解,得到了各个摩擦副在一个工作循环中的摩擦动力学性能,讨论了滑块供油孔尺寸和十字头轴承宽度对低速机摩擦动力学的影响。计算结果表明,十字头滑块承担发动机的侧推力,摩擦损失较大。十字头轴承在上止点和下止点附近摩擦功率较高。滑块供油孔的半径会影响其摩擦动力学特性。适当地降低轴承宽度,能够降低十字头轴承摩擦损失。     

Modeling of the non-uniform combustion in a scramjet engine

Due to the high-speed of the air stream, the scramjet combustion is neither uniform nor complete. An empirical fuel distribution model is developed to describe non-uniform combustion for scramjet engines. The combustor is subdivided into different regions by radius with different local equivalence ratios. The conservation equations of the regions for the combustion and exhaust expansion are computed independently. The results indicate that scramjet thrust is more related to the fuel equivalence ratio and combustion efficiency. If the combustion efficiency is 100% and the fuel equivalence ratio is constant, there is no obvious effect of different fuel distribution to the engine except for the exhaust parameter distribution. It is also revealed that the sum of isolator shock loss and combustor Rayleigh loss is nearly constant under the same isolate cross-sectional area. Lower isolator inlet Mach is benefit to the thrust performance and the best thrust performance is at the thermal choking boundary. When the isolator inlet Mach increases, the thrust decreases.     

Economic and environmental impact assessments of hybridized aircraft engines with hydrogen and other fuels

Hybridized engines have become the focus of research nowadays in order to update the existing engines in different transportation sectors. This paper presents a hybridized aircraft engine consisting of a molten carbonate fuel cell system and a commercial turbofan system. The MCFC units are connected to a steam reforming and a water gas shift system. Also, five clean fuels are selected, such as dimethyl ether, hydrogen, ethanol, methane, and methanol, which are combined with different mass ratios to form five different fuel blends. The hybridized aircraft is investigated using three approaches: exergy analysis, exergoeconomic analysis, and exergoenvironmental analysis. It is found that the proposed engine has an average exergetic efficiency of 88% and an average exergy destruction ratio of 12%. The specific exergetic cost of electricity of the engine has an average value of 710 $/GJ for the high-pressure turbine and 230$/GJ for the intermediate and low-pressure turbines, as well as 50 $/GJ for the MCFC. The average specific exergoenvironmental impact of electricity is 14 mPt/MJ for turbines and 4 mPt/MJ for the MCFC. In addition, a blend of ethanol and hydrogen appears to be a viable option economically and environmentally.     

Performance analysis of a hybrid pulse detonation engine using liquid hydrogen as fuel

Aimed at enhancing the comprehensive performance of the air turbo rocket engine (ATR), two schemes of hybrid pulse detonation engine (PDE) configurations based on the ATR were proposed. The engines are fueled by liquid hydrogen, and the oxidant is the incoming air or self-carried liquid oxygen. The ideal thermodynamic cycle processes of the engines were analyzed, and the relevant mathematical models were established. The fuel pump pressure ratio of the ATREX and the oxidant-fuel ratio of the ATR-GG are respectively used as iterative variables. The performances of the two engine schemes at the design point were obtained and compared with that of the traditional ATR. The results show that, under ideal conditions, the specific thrust and specific impulse of the hybrid PDE based on the ATREX are about 20% higher than those of the traditional ATREX. Moreover, the mass of the oxidant required by the hybrid PDE based on the ATR-GG is about 49.5% lower than that of the traditional ATR-GG, while the specific thrust and specific impulse are not reduced as compared with those of the traditional ATR-GG.     

Performance analysis of an irreversible Miller heat engine and its optimum criteria

An irreversible cycle model of the Miller heat engine is established, in which the multi-irreversibilities coming from the adiabatic compression and expansion processes, finite time processes and heat leak loss through the cylinder wall are taken into account. The power output and efficiency of the cycle are optimized with respect to the pressure ratio of the working substance. The optimum criteria of some important parameters such as the power output, efficiency and pressure ratio are given. The influence of some relevant design parameters is discussed. Moreover, it is expounded that the Otto and the Atkinson heat engines may be taken as two special cases of the Miller heat engine and that the optimal performance of the two heat engines may be directly derived from that of the Miller heat engine.     

Effect of finite heat input on the power performance of micro heat engines

Micro heat engines have attracted considerable interest in recent years for their potential exploitation as micro power sources in microsystems and portable devices. Thermodynamic modeling can predict the theoretical performance that can be potentially achieved by micro heat engine designs. An appropriate model can not only provide key information at the design stage but also indicate the potential room for improvement in existing micro heat engines. However, there are few models reported to date which are suitable for evaluating the power performance of micro heat engines. This paper presents a new thermodynamic model for determining the theoretical limit of power performance of micro heat engines with consideration to finite heat input and heat leakage. By matching the model components to those of a representative heat engine layout, the theoretical power, power density, and thermal efficiency achievable for a micro heat engine can be obtained for a given set of design parameters. The effects of key design parameters such as length and thermal conductivity of the engine material on these theoretical outputs are also investigated. Possible trade-offs among these performance objectives are discussed. Performance results derived from the developed model are compared with those of a working micro heat engine (P3) as an example.     

The control of a free-piston engine generator. Part 2: Engine dynamics and piston motion control

Free-piston engines are under investigation by a number of research groups due to potential fuel efficiency and exhaust emissions advantages over conventional technology. The main challenge with such engines is the control of the piston motion, and this has not yet been fully resolved for all types of free-piston engines. This paper builds on the fundamental investigations presented in the accompanying paper and investigates the dynamics of the engine and the feasibility of classical control approaches. The response of the engine to rapid load changes are investigated using decentralised PID, PDF and disturbance feedforward. It is found that the engine is sensitive to rapid load changes but that in constant power applications standard control techniques provide satisfactory performance. The influence of cycle-to-cycle variations in the combustion process are investigated, but not found to be critical for engine operation.     

Miniaturization limitations of HCCI internal combustion engines

Small-scale energy conversion devices are being developed for a variety of applications. Notable are propulsion units for micro-aircraft vehicles (MAV). In spite of the fact that batteries have low energy density, batteries today power most of the micro aircrafts. Their low energy density significantly limits the aircraft performances. The high specific energy of hydrocarbon and hydrogen fuels, as compared to other energy storing means, like, batteries, elastic elements, flywheels, pneumatics, and fuel cells, appears to be an important advantage, and favors the internal-combustion-engine (ICE) as a candidate. In addition, the specific power (power per unit of mass) of the ICE is much higher than that of other candidates like fuel cells, photovoltaic, and battery units. Micro-engines are not simply smaller versions of full-size engines. Physical processes such as combustion, gas exchange, and heat transfer, are performed in regimes different from those occur in full-size engines. Consequently, engine design principles are different at a fundamental level, and have to be re-considered before they are applied to micro-engines. When a spark-ignition (SI) cycle is considered, part of the energy that is released during combustion is used to heat-up the mixture in the quenching volume, and therefore the flame-zone temperature is lower and in some cases can theoretically fall below the self-sustained combustion temperature. The flame quenching thus seems to limit the minimum dimensions of a SI engine. This limit becomes irrelevant when a homogeneous-charge compression-ignition (HCCI) cycle is considered. In this case friction losses and charge leakage through the cylinder-piston gap become dominant, constrain the engine size, and impose minimum engine speed limits. In the present work a phenomenological model has been developed to consider the relevant processes inside the cylinder of a homogeneous-charge compression-ignition (HCCI) engine. The lower possible limits of scaling-down HCCI cycle engines are proposed. The present work postulates the inter-relationships between the pertinent parameters, and proposes the lower possible miniaturization limits of IC engines.