跨声速离心压气机机匣处理扩稳研究

高增压技术是高升功率车用内燃机的主要技术瓶颈之一,其核心难点在于高压比离心压气机内部复杂跨声速流动导致稳定运行范围窄,无法满足车用工况在高压比条件下对稳定运行工作范围的要求。为拓宽跨声速离心压气机的稳定工作范围,利用全三维数值模拟研究了机匣处理几何参数对扩稳的作用规律及机理。试验结果表明,采用优化后的机匣处理结构,压气机稳定工作范围由20.8%提高到33.6%。     

新型热声谐振机构的理论分析和实验验证

谐振管作为热声发动机的重要组成部分,其长度占整个系统轴向长度的大部分。本文提出了一种利用液体和弹性膜组成谐振系统的方法,并使用这种谐振系统取代谐振管,使系统轴向尺寸减少为原来的1/5。文中利用线性热声理论对该谐振系统的谐振频率进行了计算,并对不同阻尼系数对系统的耗散做出了分析。实验结果表明,在利用驻波热声发动机驱动的情况下,谐振系统自激起振,谐振频率为360 Hz,实际谐振频率与计算值误差在5%以内。     

Thermodynamic Performance Characteristics of a Brownian Microscopic Heat Engine Driven by Discrete and Periodic Temperature Field

A Brownian microscopic heat engine with a particle hopping on a one-dimensional lattice driven by a discrete and periodic temperature field in a periodic sawtooth potential is investigated. In order to clarify the underlying physical pictures of the heat engine, the heat flow via the potential energy and the kinetic energy of the particles are considered simultaneously. Based on describing the jumps among the three states, the expressions of the efficiency and power output of the heat engine are derived analytically. The general performance characteristic curves are plotted by numerical calculation. It is found that the power output-efficiency curve is a loop-shaped one, which is similar to one for a real irreversible heat engine. The influence of the ratio of the temperature of the hot and cold reservoirs and the sawtooth potential on the maximum efficiency and power output is analyzed for some given parameters. When the heat flows via the kinetic energy is neglected, the power output-efficiency curve is an open-shaped one, which is similar to one for an endroeversible heat engine.     

3-D simulation of soot formation in a direct-injection diesel engine based on a comprehensive chemical mechanism and method of moments

Here, we propose both a comprehensive chemical mechanism and a reduced mechanism for a three-dimensional combustion simulation, describing the formation of polycyclic aromatic hydrocarbons (PAHs), in a direct-injection diesel engine. A soot model based on the reduced mechanism and a method of moments is also presented. The turbulent diffusion flame and PAH formation in the diesel engine were modelled using the reduced mechanism based on the detailed mechanism using a fixed wall temperature as a boundary condition. The spatial distribution of PAH concentrations and the characteristic parameters for soot formation in the engine cylinder were obtained by coupling a detailed chemical kinetic model with the three-dimensional computational fluid dynamic (CFD) model. Comparison of the simulated results with limited experimental data shows that the chemical mechanisms and soot model are realistic and correctly describe the basic physics of diesel combustion but require further development to improve their accuracy.     

Understanding the effect of inhomogeneous fuel–air mixing on knocking characteristics of various ethanol reference fuels with RON 100 using rapid compression machine

We investigated the effect of inhomogeneous mixing of a fuel–air mixture in a spark-ignition engine on knocking characteristics and the dependency of the effect on the fuel, especially for various ethanol reference fuels with a fixed RON of 100. We assumed that a locally lean spot and rich spots exist in the end gas owing to inhomogeneous mixing and calculated their thermodynamic states with a multizone spark-ignition engine simulation. Subsequently, the ignition delay around the state was measured using a rapid compression machine at varying temperatures and equivalence ratios. The obtained results were processed to calculate ξ, which is the ratio of sound speed to auto-ignition propagation speed, and $?$, defined as the time required for acoustic front to exit the hot spot divided by the excitation time. Then, we analyzed the knocking occurrence and intensity from the locally lean spot and rich spots based on Zel'dovich and Bradley's ξ–$?$ theory. Our results show that the lean spot has a shorter ignition delay than the stoichiometric mixture (ξ?>?0) regardless of the ethanol content, whereas the rich spot does not (ξ?<?0), implying that only the lean spot can initiate knocking. This is because the temperature of the lean spot is higher than the surrounding mixture owing to its higher specific heat ratio and less charge cooling effect. In addition, the knocking intensity from the lean spot is found to be maximized with ERF0, showing the largest ${\xi }^{?2}$ value. Further analysis was conducted by dividing ξ into the effect of the temperature gradient, ξ_T, and that of the equivalence ratio gradient, ξ_?. Consequently, we found that the magnitude of ξ_T is related to the activation energy of the fuel, while that of ξ_? is determined by the dependency of the pre-heat release characteristics of the fuel on the equivalence ratio.     

Hysteretic behavior induced by an electroacoustic feedback loop in a thermo-acousto-electric generator

An active control method of the spatial distribution of the acoustic field is applied in a thermo-acousto-electric generator. An auxiliary acoustic source is used to force the self-sustained thermoacoustic oscillation in order to control the thermoacoustic amplification. The auxiliary source consists of a loudspeaker, located inside the loop-tube close to the main ambient heat exchanger, and supplied with a delayed signal through an electric feedback loop, comprising a phase-shifter and an amplifier, connected to a reference microphone. Experiments are performed on a prototype engine working with air at a static gauge pressure of 5 bars. Experimental results demonstrate how it is possible to tune the acoustic oscillations in order to increase the global performance of the generator, compared to the case without control, as well as the existence of a hysteretic behavior induced by the electroacoustic feedback loop itself, which leads to a discrepancy between the onset heat input and the offset one.     

关于教材中热力学第二定律的若干逻辑问题

指出了一些物理化学教材在叙述热力学第二定律时存在的若干逻辑问题,表明它们违反了逻辑学中的同一律、不矛盾律和充足理由律。并从历史的角度简述了Carnot循环和Carnot机效率公式的由来。     

相对主元分析在船舶机舱监控系统的应用

目前船员对于船舶状况、航行状态等的判断主要还是依靠经验,难免会出现不恰当的决策,造成不必要的人力、财力的损失;针对这一问题提出并开发了一套融入相对主元分析船舶机舱监控系统;该系统除了具有常规机舱监控系统功能外,还能实现故障监测功能;协助管理人员进行系统故障的分析,从而更好地保证船舶航行的安全与效率,减少人为误操作带来的事故问题;增强了船舶监控系统的功能,大大提高了人员的工作效率减轻了人员的劳动强度;其设计满足船级社的定期无人机舱值守操作,为机舱监控系统的设计提供了一种新的思路。     

Visualization of Crevice Flow in an Engine Using Laser-Induced Fluorescence

A simultaneous visualization technique of reacting and unburned zones using laser-induced fluorescence (LIF) was applied to a high-pressure combustion field in an engine cylinder. Crevice flow from a crevice between a piston and a cylinder wall of a spark ignition gas engine was visualized by LIF of OH and acetone. OH was excited simultaneously with acetone that was seeded into fuel as a tracer by an excitation light at 283.92 nm. Fluorescence signals from each species were detected individually by two intensified CCD cameras using optical band-pass filters which transmit fluorescence wavelength of OH and acetone, respectively. Pressure- and temperature-dependence of LIF signals from each species were evaluated. From the visualized images, it was clarified that oxidation of the crevice flow is stopped at the time of exhaust valve opening. Effects of exhaust port pressure on the oxidation process were investigated.     

白铜弹簧丝两级载荷下累积疲劳损伤预测模型

通过对文献中白铜弹簧丝疲劳寿命试验数据的分析,给出了具带存活率的疲劳寿命曲线表达式。在此基础上,建立了两级载荷下累积疲劳损伤及概率分布的预测模型。