二冲程液压自由活塞发动机换气过程影响因素的仿真研究

利用CONVERGE软件建立了二冲程液压自由活塞发动机换气过程的三维计算流体动力学（computational fluid dynamics, CFD）仿真模型，并且基于液压自由活塞发动机的独特结构，研究了气口比时面值、扫气箱压缩比、活塞顶倾角和活塞杆直径对换气过程的影响。结果表明：在未发生废气倒流时，扫气效率主要与扫气比时面值有关，增大扫气比时面值有利于提高扫气效率；捕获率主要与排气比时面值有关，减小排气比时面值有利于增大捕获率；提高扫气箱压缩比有利于提高扫气效率，扫气箱压缩比从1.2增加到2.1，扫气效率提升9.8%；适当增大活塞顶倾角有利于扫气效率和捕获率的提高；减小活塞杆直径有利于提升扫气效率，但同时会导致捕获率下降。     

对置活塞二冲程柴油机换气过程的试验

针对对置活塞二冲程柴油机换气特点和示踪气体法测试原理,提出了示踪气体法在对置活塞二冲程柴油机上的具体试验方法.利用该方法开展了发动机换气过程的试验研究,分析了不同运转工况下进、排气状态参数对发动机换气品质的影响规律.结果表明:进、排气压差对换气品质及捕获空气量有较大的影响,压差越大,扫气效率和捕获空气量越高;当给气比大于1.4以后,压差对扫气效率和捕获空气量的影响趋势逐渐趋于平缓;以发动机稳定运行并兼顾较小的泵气损失为优化目标,给气比宜选取的范围为0.5~1.4.     

对置活塞二冲程柴油机扫气系统优化方法研究

分析了对置二冲程柴油机扫气系统参数对发动机工作过程特征参数的影响规律,分别提出了以扫气效率为优化目标和以平均指示压力(IMEP)为优化目标的优化函数。结合正交优化方法,优化计算并对比分析不同优化函数的优缺点。研究结果表明:IMEP可有效地兼顾扫气系统参数对扫气效率与发动机指示热效率的影响,更适合作为对置二冲程柴油机扫气系统优化目标。优化结果显示:扫气口宽度比为0.85,排气口宽度比为0.6,扫气口高度为22mm,排气口高度为29mm,扫气口倾角为10°时发动机IMEP达到最优值。     

小型二冲程汽油机气口主要参数的计算和确定

本文以气口的比时面值为中心 ,系统地介绍了化油器式曲轴箱回流扫气小型二冲程汽油机对称配气正时气口各个主要参数的计算和确定问题。首先介绍了所需要的气口比时面值的计算和确定方法 ,其中对最早由A·C·奥尔林提出 ,现被我国内燃机教科书和设计手册采用 ,由气体流量方程式推导出的计算公式进行了修正 ,使其计算结果与现有小型二冲程汽油机的现实数据相一致。随后介绍了一种已知结构和运转参数 ,计算比时面值的新方法———系数计算法。最后介绍了由给定比时面值计算其所需气口配气相位角和气口高度的方法 ,填补了这方面的空白     

1E160W 型气体燃料发动机换气过程的试验研究

本文介绍了一台曲轴箱回流扫气的二冲程天然气发动机换气过程的试验研究。文中着重介绍了水模拟动态扫气试验的原理、设备、方法和结果。并对测取扫气图试验方法和水模拟动态扫气试验方法进行了比较。最后介绍了此种测试方法在实际样机改进中应用时的效果。     

小型二冲程汽油机气口主要参数的计算和确定

本文以气口的比时面值为中心,系统地介绍了化油器式曲轴箱回流扫气小型二冲程汽油机对称配气正时气口各个主要参数的计算和确定问题。     

液压自由活塞发动机直流扫气设计及优化研究

基于气门-气口直流扫气方式的设计及自由活塞本身运行特点设计了液压气门的控制策略,通过试验对气门控制策略进行了验证并获取了缸内压力及活塞运行曲线。将获取的部分试验数据作为三维仿真的边界条件,通过AVL FIRE ENGINE PLUS建立的三维仿真模型探讨了排气门正时、气口高度及扫气压力对给气比、捕获率及扫气效率的影响规律。在此基础之上,提出了一种基于给气比、捕获率及扫气效率的优化函数,优化计算结果表明:当扫气压力ps为0.16MPa、扫气口高度hs为26mm、排气门开启角EVO为48mm时,液压自由活塞发动机最大扫气效率ηs可达到84.7%。     

小型二冲程发动机电控汽油喷射分层扫气系统的研究

为减少小型二冲程发动机扫气短路损失,降低发动机的油耗和排放,研究开发了二冲程发动机电控汽油喷射分层扫气系统,并阐述了该系统的工作原理,通过对５０ｍＬ发动机原机,进气管电控喷射和电控汽油喷射分层扫气系统３种方案的对比试验,讨论了不同负荷时分层扫气系统对发动机性能的影响,表明电控汽油喷射分层扫气系统能够低发动机油耗２５％－４０％,ＨＣ排放４０％以上,但ＣＯ排放有明显上升。     

顶置气门式二冲程发动机的开发

本文介绍新开发１．３Ｌ４缸顶置气门式二冲程发动机，并从功率、燃油消耗率和排放等方面阐明了二冲程发动机的潜力。燃油直接被喷射到气缸内，然后靠扫气泵对已燃气体进行扫气。我们注意到混合气浓度下降对燃烧的影响。浓度比的最佳化与适度的换气有密切关系，因为高浓度比会引起自发点火和过度的换气损失。     

对置二冲程柴油机扫气口参数对扫气过程的影响

通过分析扫气口高度、圆周利用率、气口径向倾角等参数对对置二冲程柴油机扫气过程的影响,建立了基于GT-Power的一维仿真模型,研究分析了扫气口高度、圆周利用率变化对发动机扫气过程的影响;同时建立基于AVL-FIRE的对置二冲程柴油机扫气过程CFD仿真模型,研究了气口径向倾角变化对发动机扫气过程的影响。研究结果表明:扫气过程中,扫气流量主要受扫气口开启面积大小的影响,并随着扫气口开启面积的增大而增大;适当的扫气口倾角能促进扫气过程中的新鲜充量和废气的分层,但是扫气倾角太大容易导致气缸中心空气密度低,残余废气易聚集难以排出气缸;当扫气倾角为20°时扫气效率最大。     

An experimental study on the backfire occurrence and combustion stabilization of high-efficiency hydrogen-fueled free-piston linear power systems

A scavenging method suitable for high-efficiency hydrogen (H₂)-fueled two-stroke free-piston linear power systems as a next-generation alternative engine is experimentally studied, investigating the driving and backfire suppression characteristics of various scavenging methods by using a rapid compression expansion machine. A simple structured loop-scavenging method which was expected to be unfavorable for suppressing backfire in H₂-fueled power systems is more advantageous than the valve-driven scavenging methods when the system performance is evaluated together. For the loop-scavenging method, no backfire is observed at the fuel-equivalence ratio φ ≤ 0.6 when the ignition timing IGT is set for the maximum pressure (MPT) and the backfire limit can be extended to φ = 0.8 if IGT is advanced than MPT, showing the maximum indicated thermal efficiency of 48%. The performance test using a single-type H₂-fueled free-piston linear power system adopting the loop-scavenging successfully demonstrates stable continuous operation with no backfire at φ ≤ 0.8.     

车用柴油机4气门结构设计研究

运用一维气体流动模拟软件BOOST,对某公司的一款2气门柴油机改成4气门后的流动过程建立计算模型,对改型后柴油机的主要结构参数,如气门直径、气道直径、歧管直径、配气相位进行换气过程模拟计算。当该机采用直径分别为39．0mm的进气门、37．5～30．0mm的渐缩进气道、53．0mm的进气歧管、32．5mm的排气门、23．0mm的等直径排气管、32．5mm的排气歧管时可以获得较好的换气性能。通过对配气相位进行改进和优化,可以在整个转速范围内得到较理想的换气性能。     

柴油机燃用甲醇/柴油混合燃料的参数优化

对柴油机的供油系统参数（包括启喷压力、供油提前角和每循环供油量）进行优化,采用EGR来进一步降低NOx排放。结果表明：经过供油参数优化后混合燃料柴油机的动力性和经济性与原机相当,但碳烟排放的最大降幅达到15.4%,NOx排放的最大降幅达到28.25%。     

非道路涡轮增压柴油机高原适应性研究

为改善非道路柴油机高海拔条件下功率下降、经济性及排放性能恶化、高速增压器超速等问题,利用柴油机高原环境模拟台架试验结合一维仿真研究了0～4 000m海拔环境下增压器运行特性、柴油机综合性能参数等随海拔高度的变化规律及影响机理。针对柴油机的变海拔性能恢复目标,通过对增压系统进行参数计算和选配,提出一种带有废气旁通阀的两级涡轮增压匹配方案。研究结果表明:变海拔条件下,非道路柴油机各性能参数呈现非线性变化,在转速800～2 800r/min全负荷工况下,柴油机动力性、经济性变化梯度呈现出先减小后增大的"浴盆形"趋势。在0～2 000m海拔环境下,柴油机转矩降幅达4.3%,有效燃油消耗率降幅达6%。随着海拔升高,中冷前温度与涡前温度逐渐升高,增压压力与涡前压力逐渐降低,CO、全碳氢和NO_x排放升高。匹配两级增压系统后,对比原机4 000m海拔运行工况,柴油机功率平均升高14.9%,有效燃油消耗率平均降低11.8%,实现了非道路柴油机的高海拔性能恢复目标。     

天然气发动机可变气门定时的仿真研究

利用GT-Power软件建立了天然气发动机仿真模型,并对其进排气门的配气相位进行优化,研究并预测了配气相位优化前后发动机充量系数及功率的变化规律.对该天然气发动机的计算结果表明,采用可变气门定时(VVT)技术后,发动机的功率有明显提高,尤其是在中低转速时,功率提高达到10%以上,大大改善了发动机的动力性能.     

二冲程汽油机扫气过程多维数值模拟及扫气系统优化设计

本文采用多维数值模拟方法对二冲程发动机的扫气过程进行优化。对原型机(小型HS-510航空发动机)的扫气过程数值模拟发现：在缸内存在环流和涡流。环流在贴近气缸附近较强，可以将废气排出气缸；而在气缸中部较弱，难以将废气彻底排出。涡流的存在则降低了发动机的扫气效率。原型机的扫气过程同理想的扫气过程相比有相当大的差距。在原型机扫气过程数值模拟的基础上，改进扫气系统设计，将扫气口由原来的两个增加到五个。对改型机数值模拟发现缸内没有形成涡流。计算和试验结果表明发动机的扫气效率得到了提高，且发动机的功率提高11％。     

V型柴油机采用定压和脉冲增压系统对性能影响的比较

在一台高速12缸柴油机提高转速功率的改进设计过程中，应用性能分析软件AVL-B00ST对该机采用不同增压系统对性能的影响进行了分析计算比较。并以满足功率、油耗、排温及爆压等指标要求为目标，为对压缩比、增压压力、排气系统等进行优化，提高柴油机性能提供综合依据与改进方向。     

Optimization of Output Power and Thermal Efficiency of Solar‐Dish Stirling Engine Using Finite Time Thermodynamic Analysis

This paper presents an investigation on finite time thermodynamic (FTT) evaluation of a solar‐dish Stirling heat engine. FTTs has been applied to determine the output power and the corresponding thermal efficiency, exergetic efficiency, and the rate of entropy generation of a solar Stirling system with a finite rate of heat transfer, regenerative heat loss, conductive thermal bridging loss, and finite regeneration process time. Further imperfect performance of the dish collector and convective/radiative heat transfer mechanisms in the hot end as well as the convective heat transfer in the heat sink of the engine are considered in the developed model. The output power of the engine is maximized while the highest temperature of the engine is considered as a design parameter. In addition, thermal efficiency, exergetic efficiency, and the rate of entropy generation corresponding to the optimum value of the output power is evaluated. Results imply that the optimized absorber temperature is some where between 850 K and 1000 K. Sensitivity of results against variations of the system parameters are studied in detail. The present analysis provides a good theoretical guidance for the designing of dish collectors and operating the Stirling heat engine system.     

Multi-dimensional scavenging analysis of a free-piston linear alternator based on numerical simulation

A free-piston linear alternator (FPLA) is being developed by the Beijing Institute of Technology to improve the thermal efficiency relative to conventional crank-driven engines. A two-stroke scavenging process recharges the engine and is crucial to realizing the continuous operation of a free-piston engine. In order to study the FPLA scavenging process, the scavenging system was configured using computational fluid dynamics. As the piston dynamics of the FPLA are different to conventional crank-driven two-stroke engines, a time-based numerical simulation program was built using Matlab to define the piston’s motion profiles. A wide range of design and operating options were investigated including effective stroke length, valve overlapping distance, operating frequency and charging pressure to find out their effects on the scavenging performance. The results indicate that a combination of high effective stroke length to bore ratio and long valve overlapping distance with a low supercharging pressure has the potential to achieve high scavenging and trapping efficiencies with low short-circuiting losses.     

Prototype testing and analysis of a novel internal combustion linear generator integrated power system

A novel four-stroke free-piston engine equipped with a linear electric generator (namely internal combustion linear generator integrated power system) is proposed in this paper to achieve efficient energy conversion from fuel to electricity. Unique features of the novel power system are presented and their effects on the continuous running are discussed, along with potential advantages and disadvantages compared to conventional engines. A single cylinder, gasoline and spark ignition prototype is fabricated with reference to the geometric and control parameters of an existing conventional four-stroke engine. Stable running of the prototype is realized, and a 2.2 kW average output power with the generating efficiency of 32% has been obtained up to now. The feasibility and performance of the proposed design are verified. Detailed testing results from the continuous running prototype are analyzed in this paper for giving insight into the performance and dynamic behaviors of the novel power system.