Experimental study on compression stroke characteristics of free- piston engine generator

The compression stroke characteristics of free-piston engine generator were studied. The numerical model of the compression stroke was established based on thermodynamics and dynamics equation,and the leak loss,heat loss and friction loss were considered. Through solving numerical equations,the in-cylinder pressure of compression stroke under different compression ratios was calculated,energy transfer and conversion process was analyzed,and the calculated results were experimentally verified. The results showed that the actual effective output of electronic energy and the compression energy stored in the com-pressed gas accounted for about 70%. The compression energy gradually increased with the increasing com-pression ratio. When the compression ratio was more than 7. 5,the actual compression energy increased slowly and the energy error between simulation and test decreased.

Numerical Simulation of a Spark Ignited Two-Stroke Free-Piston Engine Generator

A numerical program is built to simulate the performance of a spark ignited two-stroke free-piston engine coupled with a linear generator. The computational model combines a series of dynamic and thermodynamic equations that are solved simultaneously to predict the performances of the engines. The dynamic analysis performed consists of an evaluation of the frictional force and load force introduced by the generator. The thermodynamic analysis used a single zone model to describe the engine＇ s working cycle which includes intake, scavenging, compression, combustion and expansion, and to evaluate the effect of heat transfer based on the first law of thermodynamics and the ideal gas state equation. Because there is no crankshaft, a time based Wiebe equation was used to express the fraction of fuel burned in the combustion. The calculated results were validated by using the experimental data from another research group. The results indicate that the free-piston generator has some advantages over conventional engines.

Emerging strategies for nerve repair and regeneration in ischemic stroke:neural stem cell therapy

Ischemic stroke is a major cause of mortality and disability worldwide,with limited treatment options available in clinical practice.The emergence of stem cell therapy has provided new hope to the field of stroke treatment via the restoration of brain neuron function.Exogenous neural stem cells are beneficial not only in cell replacement but also through the bystander effect.Neural stem cells regulate multiple physiological responses,including nerve repair,endogenous regeneration,immune function,and blood-brain barrier permeability,through the secretion of bioactive substances,including extracellular vesicles/exosomes.However,due to the complex microenvironment of ischemic cerebrovascular events and the low survival rate of neural stem cells following transplantation,limitations in the treatment effect remain unresolved.In this paper,we provide a detailed summary of the potential mechanisms of neural stem cell therapy for the treatment of ischemic stroke,review current neural stem cell therapeutic strategies and clinical trial results,and summarize the latest advancements in neural stem cell engineering to improve the survival rate of neural stem cells.We hope that this review could help provide insight into the therapeutic potential of neural stem cells and guide future scientific endeavors on neural stem cells.

A High-Efficiency Two-Stroke Engine Concept: The Boosted Uniflow Scavenged Direct-Injection Gasoline (BUSDIG) Engine with Air Hybrid Operation

A novel two-stroke boosted uniflow scavenged direct-injection gasoline (BUSDIG) engine has been proposed and designed in order to achieve aggressive engine downsizing and down-speeding for higher engine performance and efficiency. In this paper, the design and development of the BUSDIG engine are outlined discussed and the key findings are summarized to highlight the progress of the development of the proposed two-stroke BUSDIG engine. In order to maximize the scavenging performance and produce sufficient in-cylinder flow motions for the fuel/air mixing process in the two-stroke BUSDIG engine, the engine bore/stroke ratio, intake scavenge port angles, and intake plenum design were optimized by three-dimensional (3D) computational fluid dynamics (CFD) simulations. The effects of the opening profiles of the scavenge ports and exhaust valves on controlling the scavenging process were also investigated. In order to achieve optimal in-cylinder fuel stratification, the mixture-formation processes by different injection strategies were studied by using CFD simulations with a calibrated Reitz–Diwakar breakup model. Based on the optimal design of the BUSDIG engine, one-dimensional (1D) engine simulations were performed in Ricardo WAVE. The results showed that a maximum brake thermal efficiency of 47.2% can be achieved for the two-stroke BUSDIG engine with lean combustion and water injection. A peak brake toque of 379 N·m and a peak brake power density of 112 kW·L^-1 were achieved at 1600 and 4000 r·min^-1, respectively, in the BUSDIG engine with the stoichiometric condition.

Combustion Characteristics and Emission of a Two-Stroke Compression Ignition Engine with Two-Stage Injection

In order to study the effect of two-stage injection on two-stroke diesel engines, a well characterized research engine equipped with electronically controlled common rail system and scavenging system was constructed. Through analysis of combustion and emissions, two-stage injection shows its advantages. Compared with the standard injection, it produces less emissions, while compared with single early injection, it expands engine operation range. Further experiments were carried out to study the influence of several injection control parameters on two-stage injection. The fuel in the first injection is used for forming homogeneous mixture. The fuel in the second injection keeps combustion, and it is the main source of smoke emissions. NO_x is formed in both combustion process caused by these two injections, and there is an optimum fuel allocation ration to produce minimum NO_x. The cylinder pressure decreases, and the combustion is depressed with the increasing of scavenging pressure. By optimizing the injection control parameters of two-stage injection, NO_x and smoke can be reduced beyond 30% simultaneously.

Impact of Degrees of Freedom of Polyatomic Ideal Gas on Efficiency of Three-Stroke-Cycle Heat Engines

It is customary to evaluate the efficiency of four-stroke-cycle heat engines such as Carnot, Otto and Diesel with a working ideal gas [1] [2] [3]. Here we consider various three-stroke-cycle heat engines that are composed of three out of four special processes: adiabatic, isothermal, isobaric and isochoric. We deviate from the customary norm considering the working material to be a polyatomic ideal gas with various degrees of freedom. We develop analytic expressions for the efficiency of each design as a function of degrees of freedom. For suitable practical values of relevant (V, P, T), we evaluate the corresponding efficiencies.

Frequency compensation control method for opposedpiston two-stroke folded-cranktrain engine's common rail system by loop-shaping theory

A frequency compensation control method for the opposed-piston two-stroke folded-cranktrain（ OPFC） diesel engine＇s common rail system is presented as a result of the study of the loop-shaping theory. A common rail working process and the classical frequency control theory are combined to construct a frequency restriction of common rail pressure. A frequency compensator is utilized to improve the robustness of multiplicative perturbations and disturbance. The loop-shaping method has been applied to design the common rail pressure controller of the OPFC diesel engine. Simulation and bench test results show that in the condition of perturbation that comes from the effect of injection,multi-injection,fuel pumping of a pre-cylinder,and instantaneous pressure fluctuation,the controller indicates high precision. Compared with the original controller,this method improves the control precision by 67. 3%.

Bioorthogonal microglia-inspired mesenchymal stem cell bioengineering system creates livable niches for enhancing ischemic stroke recovery via the hormesis

Mesenchymal stem cells(MSCs)experience substantial viability issues in the stroke infarct region,limiting their therapeutic efficacy and clinical translation.High levels of deadly reactive oxygen radicals(ROS)and proinflammatory cytokines(PC)in the infarct milieu kill transplanted MSCs,whereas low levels of beneficial ROS and PC stimulate and improve engrafted MSCs’viability.Based on the intrinsic hormesis effects in cellular biology,we built a microglia-inspired MSC bioengineering system to transform detrimental high-level ROS and PC into vitality enhancers for strengthening MSC therapy.This system is achieved by bioorthogonally arming metabolic glycoengineered MSCs with microglial membrane-coated nanoparticles and an antioxidative extracellular protective layer.In this system,extracellular ROSscavenging and PC-absorbing layers effectively buffer the deleterious effects and establish a microlivable niche at the level of a single MSC for transplantation.Meanwhile,the infarct’s inanimate milieu is transformed at the tissue level into a new living niche to facilitate healing.The engineered MSCs achieved viability five times higher than natural MSCs at seven days after transplantation and exhibited a superior therapeutic effect for stroke recovery up to 28 days.This vitality-augmented system demonstrates the potential to accelerate the clinical translation of MSC treatment and boost stroke recovery.

Influence of Combustion Chamber Design Parameters and Intake Environments on Spark Ignition Engine Performance and Exhaust Gas Emission

In the present paper, the effect of the combustion chamber design parameters on the improvement of combustion efficiency (the heat generated inside the combustion chamber) and the enhancement in the pollution rates (heat emissions) from a four-stroke, spark-ignition engine has been studied experimentally and theoretically. Two different programs, Gaseq and Ansys, were used to simulate the effect of the combustion chamber shape, turbulent kinetic energy, intake temperature, intake pressure, parity ratio, compression ratio, and engine speed on reducing specific fuel consumption in the engine, reducing carbon dioxide emissions, and increasing overall engine efficiency. The results showed increasing the intake temperature increased the amount of heat produced in the combustion chamber. This leads to increases in the overall efficiency of the engine, but leads to increasing the carbon dioxide and nitrogen oxide emissions. Increasing the intake pressure has a positive effect on the combustion temperature and pressure, but it has a negative effect on carbon dioxide and nitrogen oxides. Raising the pressure ratio improved the overall efficiency of the engine by increasing the combustion heat, but increasing specific fuel consumption and emissions. Also, increasing the engine speed above the permissible limit has an adverse effect on the spraying speed due to the piston speed being higher than the flame speed, which leads to a reduction in the engine brake torque. An increase in the compression ratio leads to higher fluid pressure and output capacity, but combustion methods occur. An increase in the kinetic energy of the turbulence leads to good combustion. A bowl in a piston has the highest rate of rotation and rotation compared to flat and hemispherical pistons. That is, the design of the cylinder head of this type leads to an improvement in the combustion efficiency and thus the efficiency of the engine.

Auto-Ignition and Heat Release Correlations for Controlled Auto-Ignition Combustion in Gasoline Engines

Auto-ignition and heat release correlations for controlled auto-ignition(CAI)combustion were derived from extensive in-cylinder pressure data of a four-stroke gasoline engine operating in CAI combustion mode.Abundant experiments were carried out under a wide range of air/fuel ratio,speed and residual gas fraction to ensure that the combustion correlations can be used in the entire CAI engine operation range.Furthermore,a more accurate method to compute the residual gas fraction was proposed by calculating the working fluid temperature at the exhaust valve close timing in the experiments.The heat release correlation was described in two parts,one is for the first slower heat release process at low temperature,and the other is for the second faster heat release process at high temperature.Finally the heat release correlation was evaluated on the single cylinder gasoline engine running with CAI combustion by comparing the experimental data with the 1-D engine simulation results obtained with the aid of the GT-Power simulation program.The results show that the predicted loads and ignition timings match closely with the measurements.

二冲程半直喷航空发动机喷油策略研究

基于自主研发的二冲程低压半直喷航空发动机及控制系统,开展喷油控制策略及对发动机性能影响规律的研究。结果表明:对于不同的发动机运行工况,需要采取不同的喷油策略组合。在起动和怠速工况,采用进气道喷射的独立供油方式;在部分负荷及高负荷工况,采用进气道喷射和缸内直喷协同供油方式,随着发动机直喷比例的提高,燃油消耗率相应减小;与采用进气道喷射供油相比较,采用低压半直喷供油可以获得较理想的燃油经济性。

动态气门运行特性及二冲程制动性能耦合研究

基于自主研发的变模式气门驱动装置,进行发动机和该气门驱动装置联合仿真,研究了二者的强耦合运行特性,为该装置的装机应用提供理论依据.研究结果表明:缸内压力和气门运行之间的强耦合关系在上止点附近排气门运行阶段尤为明显,尤其是在2300 r/min以下,发动机转速越高,气门动态升程损失程度越大,最大缸内压力越高;高于该转速后,二者变化程度逐渐减小;排气制动凸轮在上止点后设置过渡升程可消除排气门反跳的问题,并且可进一步改善制动功率和最大缸内压力之间的矛盾关系;与理想四冲程制动相比,二冲程制动的制动功率明显增加,最大缸内压力明显降低,发动机转速分别为1600、1900和2400 r/min时,实际二冲程制动功率分别提高了35.94%、45.61%和27.54%,最大缸内压力分别降低了45.42%、27.20%和7.35%.

压燃式二冲程对置活塞转盘发动机一维性能仿真

二冲程对置活塞转盘(2S-OPCP)发动机是一种新型发动机.该发动机使用凸轮转盘机构替代了传统发动机中的曲柄连杆机构,这种特殊的结构使转盘发动机具有功率密度高、体积小和结构简单等优点.发动机两侧的凸轮转盘存在相对转角,通过改变凸轮相对转角θ可以改变发动机的有效压缩比及换气正时,从而影响发动机的性能.根据转盘发动机的结构特点及工作过程搭建了一维热力学仿真模型,并使用试验数据对模型的缸内压力曲线进行了标定.随着θ改变,发动机的扫气过程及性能表现都会发生变化.当θ在0°~10°内变化时,发动机的换气过程有所改善,给气比在θ=7°时最高,提升了3.5%.同时,在θ达到4°后,指示燃油消耗率(ISFC)开始逐渐增加,ISFC最高增加了3.5%(θ=10°);而平均有效压力(IMEP)最高增加了3.3%(θ=4°),之后随着θ的上升,IMEP开始降低.

二冲程自由活塞发动机扫气过程仿真分析

点燃式二冲程自由活塞发动机扫气过程直接影响发动机的工作性能,故在建立分析模型的基础上,采用数值计算的方法对影响扫气过程的相关因素进行了分析。结果表明:采用外部供气方式适当提高进气压力可以有效提高扫气效率,增加缸内气体质量;当发动机转速存在波动时,较低转速有利于扫气过程的完成,但对缸内气体质量影响不大;当活塞行程小于设计值时,扫气效果变差,缸内气体质量明显下降。

The use of hydrogel-delivered extracellular vesicles in recovery of motor function in stroke:a testable experimental hypothesis for clinical translation including behavioral and neuroimaging assessment approaches

Neural tissue engineering,nanotechnology and neuroregeneration are diverse biomedical disciplines that have been working together in recent decades to solve the complex problems linked to central nervous system(CNS)repair.It is known that the CNS demonstrates a very limited regenerative capacity because of a microenvironment that impedes effective regenerative processes,making development of CNS therapeutics challenging.Given the high prevalence of CNS conditions such as stroke that damage the brain and place a severe burden on afflicted individuals and on society,it is of utmost significance to explore the optimum methodologies for finding treatments that could be applied to humans for restoration of function to pre-injury levels.Extracellular vesicles(EVs),also known as exosomes,when derived from mesenchymal stem cells,are one of the most promising approaches that have been attempted thus far,as EVs deliver factors that stimulate recovery by acting at the nanoscale level on intercellular communication while avoiding the risks linked to stem cell transplantation.At the same time,advances in tissue engineering and regenerative medicine have offered the potential of using hydrogels as bio-scaffolds in order to provide the stroma required for neural repair to occur,as well as the release of biomolecules facilitating or inducing the reparative processes.This review introduces a novel experimental hypothesis regarding the benefits that could be offered if EVs were to be combined with biocompatible injectable hydrogels.The rationale behind this hypothesis is presented,analyzing how a hydrogel might prolong the retention of EVs and maximize the localized benefit to the brain.This sustained delivery of EVs would be coupled with essential guidance cues and structural support from the hydrogel until neural tissue remodeling and regeneration occur.Finally,the importance of including nonhuman primate models in the clinical translation pipeline,as well as the added benefit of multi-modal neuroimaging analysis to establish non-invasive,in vivo,quantifiable imagingbased biomarkers for CNS repair are discussed,aiming for more effective and safe clinical translation of such regenerative therapies to humans.

基于GT-power的五冲程发动机多目标优化

五冲程发动机独特的二次膨胀冲程提升了发动机的热效率,独特的工作特性使其适合应用于增程式汽车。为探究高/低压缸进排气正时和点火时间对五冲程发动机性能的影响,基于GT-Power建立五冲程发动机一维模型,并在限制扭矩的条件下运用DOE工具开展目标为功率最大、比燃油消耗率和NO_(x)排放最低的多目标优化。结果表明:适当地增大低压缸气门重叠角可以有效降低排气流动损失,提升废气做功的效率;最终,各个目标值分别实现了3.26%、2.50%和0.47%的优化。多目标优化方法在五冲程发动机参数优化上的应用,保证了变量在可行域范围内实现多目标改善。

进气增压对自由活塞内燃发电机性能影响

采用增压技术可以提高现有自由活塞内燃发电机功率密度.文中针对一台自由活塞内燃发电机,建立了其一维仿真模型并根据试验数据进行了校核.通过模拟增压方式研究了进排气压力、配气相位、进排气管几何尺寸等参数对其性能的影响.设计了电动增压方案并确定了匹配参数,依据此选型了一台电动压气机.研究结果表明:当进气压力超过0.18 Mpa时,自由活塞内燃发电机有效功率超过了10 kW,给气比需保持1.3左右,扫气效率接近90%.此时扫气口需提前约0.74 ms开启,进气管容积也需适当扩大以此来保证充足的进气量和良好的换气品质.匹配结果表明在额定运行频率时自由活塞内燃发电机流通特性线穿过压气机高效区,设计点工况压气机效率超过73%.

二冲程对置发动机工作特性研究

二冲程对置发动机以其良好的功重比广泛应用于无人机、无人车等领域,采用火花点燃的工作方式使之更适合采用汽油为工作介质。文中针对装备应用需采用航空煤油的技术需求,进行了不同介质(煤油和汽油),不同喷射系统(夹气燃油喷射和气道喷射)之间的试验对比.结果表明:燃料同为汽油时,在不同节气门开度工况下,采用夹气喷射的发动机动力性优于气道喷射;只有夹气方式可以使煤油实现冷起动;进行了夹气煤油整机配机试验,在高转速工况下,节气门开度由30%提高至80%,发动机的功率和扭矩分别约增加了10 kW和65 N·m,工作过程与传统的火花点燃式发动机几近相同;最后探究了节气门控制在50%,夹气方式下煤油与汽油的性能差异对比,表明采用汽油燃料的动力性更优,功率和扭矩分别约增加了5 kW和35 N·m.

外泌体及其工程化应用于缺血性脑卒中的研究进展

缺血性脑卒中是一种致残率和死亡率极高的脑血管疾病。目前,尚无有效的治疗方法能够促进缺血性脑卒中后的神经功能恢复。外泌体既可以介导细胞之间的通信,又具有跨越血脑屏障的能力,故在缺血性脑卒中的治疗中受到广泛关注。利用生物工程技术修饰改造外泌体,制备具有脑靶向性和治疗作用的工程化外泌体,应用于缺血性脑卒中的研究与治疗,以期提高脑卒中后神经功能的修复,减少临床致残率和死亡率,提高患者的生存和生活质量。本文从外泌体、外泌体在缺血性脑卒中的作用、工程化外泌体的制备等方面进行综述,并讨论工程化外泌体在治疗缺血性脑卒中的应用前景,以期为后续研究提供参考。

二冲程点燃式航空煤油发动机爆震预测模型研究

针对二冲程点燃式航空煤油活塞发动机进行爆震预测研究,提出了一种基于3-Arrhenius公式的两组分混合爆震预测模型。以航空煤油燃烧实验数据为基础,采用GT-Power软件建立并校核了航空煤油的燃烧模型,利用一维性能仿真得到了爆震预测模型需要的末端混合气温度,通过发动机爆震实验数据评估了混合爆震预测模型和单一爆震预测模型的预测性能。结果表明:混合爆震预测模型和单一爆震预测模型预测的爆震起始角与实际的爆震起始角之间的标准误差分别为1.19°CA和3.23°CA,混合爆震预测模型能够识别燃烧初期的低压区域,对于爆震时缸内压力的突然升高有较好响应,表现出了良好的爆震预测性能。