不同转速下汽油机缸内湍流特性仿真研究

应用计算流体动力学理论,针对一款双气门单缸四冲程汽油机,对其在3500r·min~(-1)和5500r·min~(-1)两种工况下的进气、压缩及燃烧过程进行了数值仿真研究.研究结果表明:高转速时的滚流存在曲轴角度比低转速时长,但到达压缩后期滚流都已破碎,挤流成为湍流的主要表现形式;从进气中期到压缩冲程结束,低转速工况缸内湍流平均时间尺度大于高转速工况,在进气末期至压缩初期尤为突出;压缩中期缸内平均时间尺度变化较为剧烈;压缩上止点前20℃A左右缸内平均时间尺度达到谷值;点火时刻两种工况缸内长度尺度最大值均不超过0.46mm, 小于火花塞击穿放电后瞬间的火核尺寸,且最大尺度均存在于气缸进气门侧.     

汽油机缸内紊流运动控制因素的研究

利用热线风速法,研究了汽油机缸内紊流运动的部分控制因素,分析了转速、压缩比、挤气间隙、节气门开度等对缸内紊流运动的影响规律。研究结果表明,在压缩上止点附近,缸内紊流运动随转速的升高、挤气间隙的减小以及节气门开度的增大而加强,但随压缩比的升高而减弱;紊流时间尺度随转速的升高而减小,但基本不随其它参数变化;紊流空间尺度随转速的升高、挤气间隙的减小以及节气门开度的增大而增大,但随压缩比的增大而减小;转速升高时,紊流高频能量成份所占比例增大,但其它参数对紊流能量的频率分布状态影响不大。     

一种定容燃烧弹内的湍流发生系统

设计了一种定容燃烧弹内的湍流发生系统。它主要包括湍流发生系统、定容燃烧弹、孔板运动规律测量,着重介绍了其设计原理和结构特点。     

点燃式发动机紊流型燃烧室的设计与研究

摘要本文提出了一种组织点燃式发动机稀燃速燃的紊流型燃烧室,在一台自行设计改装的单缸试验机上对浴盆型、碗型、火球型、紧凑型、紊流型等五种燃烧室进行了对比试验研究,获得了采用不同燃烧室时发动机的性能、排放指标和燃烧特性参数,结果表明采用紊流型燃烧室时发动机具有最佳的综合性能指标,外特性燃油消耗率曲线平坦,最低油耗率为260g/(kW·h),HC、CO排放下降,动力性能和操纵性能得到改善.     

Comparison of ultra-fast microwave sintering and conventional thermal sintering in manufacturing of anode support solid oxide fuel cell

Ultra-fast microwave sintering in a multi-mode domestic microwave oven with selective susceptor and spacer has been proved to be an effective and facile method in the manufacturing of anode support solid oxide fuel cell (SOFC). Two anode support SOFCs were fabricated by using ultra-fast microwave sintering and conventional thermal sintering techniques, separately. The performances of the two cells were measured and compared in a temperature range of 700-800 °C. The microstructures of the two cells after the measurements were compared qualitatively based on SEM images. FIB-SEM technique was used to reconstruct the 3-D microstructure of both anode and cathode. The quantitative comparison of 3-D reconstructions shows the application potential and the advantages of microwave technique in SOFCs manufacturing.     

内燃机缸内湍流运动数值模拟研究

本采用ｋ－ε双方程湍流模型，正交贴体曲线网格，对内燃机气缸内空气湍流运动进行三维数值模拟，采用ＲＥＺＯＮＥ技术解决了进气阀与燃烧室凹坑不同偏置问题，与此同时，对缸内流场进行了ＬＤＶ测量，并将测量结果与计算值进行比较，二吻合良好，从而证明了本所开发的软件和选用的模型是可靠的。     

Turbulence and combustion interaction: High resolution local flame front structure visualization using simultaneous single-shot PLIF imaging of CH, OH, and CH2O in a piloted premixed jet flame

High resolution planar laser-induced fluorescence (PLIF) was applied to investigate the local flame front structures of turbulent premixed methane/air jet flames in order to reveal details about turbulence and flame interaction. The targeted turbulent flames were generated on a specially designed coaxial jet burner, in which low speed stoichiometric gas mixture was fed through the outer large tube to provide a laminar pilot flame for stabilization of the high speed jet flame issued through the small inner tube. By varying the inner tube flow speed and keeping the mixture composition as that of the outer tube, different flames were obtained covering both the laminar and turbulent flame regimes with different turbulent intensities. Simultaneous CH/CH₂O, and also OH PLIF images were recorded to characterize the influence of turbulence eddies on the reaction zone structure, with a spatial resolution of about 40 μm and temporal resolution of around 10 ns. Under all experimental conditions, the CH radicals were found to exist only in a thin layer; the CH₂O were found in the inner flame whereas the OH radicals were seen in the outer flame with the thin CH layer separating the OH and CH₂O layers. The outer OH layer is thick and it corresponds to the oxidation zone and post-flame zone; the CH₂O layer is thin in laminar flows; it becomes broad at high speed turbulent flow conditions. This phenomenon was analyzed using chemical kinetic calculations and eddy/flame interaction theory. It appears that under high turbulence intensity conditions, the small eddies in the preheat zone can transport species such as CH₂O from the reaction zones to the preheat zone. The CH₂O species are not consumed in the preheat zone due to the absence of H, O, and OH radicals by which CH₂O is to be oxidized. The CH radicals cannot exist in the preheat zone due to the rapid reactions of this species with O₂ and CO₂ in the inner-layer of the reaction zones. The local PLIF intensities were evaluated using an area integrated PLIF signal. Substantial increase of the CH₂O signal and decrease of CH signal was observed as the jet velocity increases. These observations raise new challenges to the current flamelet type models.     

内燃机气缸和燃烧室中紊流运动的测量和紊流参数的计算

摘要本文介绍了用热线风速仪测量内燃机气缸及燃烧室中的紊流运动的方法和数据的采集及处理过程.对紊流参数的计算方法进行了分析比较,讨论了平均速度和紊流强度的不同求法,探讨了采样频率的时窗宽度对计算紊流参数的影响,并对全方位测量及三维测量方法进行了比较.     

Selective atomic hydrogen heating in plasmas: Implications for quantum theory

A new model of quantum mechanics, Classical Quantum Mechanics, is based on the (nearly heretical) postulate that electrons are physical objects that obey classical physical laws. Indeed, ionization energies, excitation energies, etc. are computed based on picturing electrons as ‘bubbles’ of charge that symmetrically surround a nucleus. Hence, for example, simple algebraic expressions based on Newtonian force balances are used to predict ionization energies and stable excitation states with remarkable precision. One of the most startling predictions of the model is that there are stable ‘sizes’ of the hydrogen atom electron (bubble diameter) that are smaller (‘hydrinos') than that calculated for the ‘ground state’. Experimental evidence in support of this novel physical/classical version of quantum is alleged to be found in the existence of super-heated hydrogen atoms reported by many teams in a variety of plasmas. It is postulated that the energy required for creating super-heated H atoms comes from the shrinkage of ground state H atoms to form hydrinos. This claim is discussed with reference to a brief review of the published studies of selective Balmer series line broadening in pure H₂ and mixed gas plasmas, and astrophysical data.     

二气门汽油机缸内滚流运动湍流特性的LDA试验研究

在一台具有较强滚流比的二气门汽油机上用二维 Ｌ Ｄ Ａ测量了燃烧室内沿气缸直径方向各测点处气流运动的规律。在考虑压缩过程中缸内滚流运动会受到影响的情况下对流场进行的分析表明,压缩过程初期和中期缸内滚流仍存在,只是到了压缩末期滚流才畸变破碎。通过相关分析和谱分析,说明了这一过程的发展变化复杂。作者建议使用有效平均速度的概念来计算湍流的积分长度尺度。     

Evidence of catalytic production of hot atomic hydrogen in RF generated hydrogen/helium plasmas

A study of the line shapes of hydrogen Balmer series lines in RF generated low pressure He/H₂ plasmas produced results suggesting a catalytic process between helium and hydrogen species results in the generation of ‘hot’ (ca. 28 eV) atomic hydrogen. Even far from the electrodes ‘hot’ atomic hydrogen was predominant in He/H₂ plasmas. Line shapes, relative line areas of cold and hot atomic hydrogen (hot/cold > 2.5), were very similar for areas between the electrodes and far from the electrodes for these plasmas. In contrast, in Xe/H₂ only ‘warm’ (<5 eV) hydrogen (warm/cold < 1.0) was found between the electrodes, and only cold hydrogen away from the electrodes. Earlier postulates that preferential hydrogen line broadening in plasmas results from the acceleration of ionic hydrogen in the vicinity of electrodes, and the special charge exchange characteristics of Ar/H₂+ are clearly belied by the present results that show atomic hydrogen line shape are similar for He/H₂ plasmas throughout the relatively large cylindrical (14 cm ID × 36 cm length) cavity.     

Turbulence modelling for wall-bounded particle-laden flow with separation

The performance of different turbulence models and source-term models for the turbulent separated particle-laden flow is investigated. The accuracy of various turbulence models is firstly evaluated without any modification by the source-term model. The considered models are the k–ω SST model; the standard, the RNG and the realizable k–ε models with the standard, the non-equilibrium and the enhanced wall functions. The accuracy of various source-term models is then compared. The results are investigated and analyzed to find the best combination of the turbulence model and the source-term model in predicting the combined effects of turbulence, particles, viscous wall and flow separation. It is found that the RNG k–ε turbulence model with the non-equilibrium wall function using the source-term model of Tu and Fletcher is the most suitable combination for this type of flow.     

直喷式柴油机缸内紊流及其对柴油机性能影响的研究

本介绍了由不同几何形状的进气扰动片和燃烧室产生的进气紊流和挤压紊流对直喷式柴油机性能影响的研究。缸内紊流测量是用热线风速仪在倒拖发动机试验台上进行的。试验表明：由进气扰动片产生的进气紊流不能保持到进气终了，因此进气扰动片对柴油机性能的影响是由于进气涡流的变化所致；由燃烧室形状增强的挤压紊流可使柴油机烟度明显改善，但对燃油经济性几乎没有影响。     

Fast H in hydrogen mixed gas microwave plasmas when an atomic hydrogen supporting surface was present

Atomic hydrogen is heated to temperatures of up to two orders of magnitude greater than the electron temperature or the temperature of any other species in certain hydrogen mixed gas RF or glow discharge plasmas. A crucial test of energetic hydrogen chemistry regarding a resonant energy transfer or rt-mechanism (RTM) versus field acceleration models (FAM) as the basis of this selective isotropic heating of a population of extraordinarily high-kinetic-energy hydrogen atoms is the observation of fast H in microwave cells proven to lack a high field as shown by the complete absence of fast H (∼0.08 eV) by Jovicevic et al. [S. Jovicevic, N. Sakan, M. Ivkovic, N. Konjevic, J. Appl. Phys. 105, 013306-1 (2009)]. The RTM predicts an enhancement in the production of fast H with the presence of a surface to support a high concentration of hydrogen atoms in order to initiate the energetic hot H source reaction that then propagates isotropically throughout the plasma. In contrast to the prior results, extraordinarily fast H of greater than 4 eV (50 times that observed and deemed possible in the Evenson microwave cell by FAM advocate Jovicevic et al.) and 50% fractional population was observed as predicted for RTM using the catalytic reaction systems of He/H₂, Ar/H₂, pure H₂, and water vapor microwave plasmas when an electrically insulating, but atomic hydrogen supporting material was placed in the plasma region. Increasing concentrations of Xe in the non-catalytic Xe/H₂ system results in a significant decrease in the energy and population of fast excited-state H atoms.     

Turbulence models application on CFD simulation of hydrodynamics,heat and mass transfer in a structured packing

In this study, turbulence model applications on two-phase flow simulation in a structured packing are investigated using CFD application. Dry pressure drop, irrigated pressure drop, mass transfer and heat transfer are studied by k–ε, RNG k–ε, k–ω and BSL turbulence models. The best results obtained by k–ω and BSL models, but k–ω is recommended because it is more robust than BSL. The mean absolute relative error (MARE) between CFD prediction of k–ω model and experimental data for dry pressure drop, irrigated pressure drop, mass transfer and heat transfer are 16.9%, 10.7%, 8.1%, 0.9%, respectively.     

Turbulence modeling of atmospheric boundary layer flow over complex terrain: a comparison of models at wind tunnel and full scale

The aim of this work is to evaluate the performance of two popular k ? ? turbulence closure schemes for atmospheric boundary layer (ABL) flow over hills and valleys and to investigate the effect of using ABL‐modified model constants. The standard k ? ? and the RNG k ? ? models are used to simulate flow over the two‐dimensional analytical shapes from the RUSHIL and RUSHVAL wind tunnel experiments. Furthermore, the mean turbulent flow over the real complex terrain of Blashaval hill is simulated and the results verified with a data set of full‐scale measurements. In general, all models yield similar results. However, use of ABL‐modified constants in both models tends to decrease the predicted velocity and increase the predicted turbulent kinetic energy. Copyright © 2010 John Wiley & Sons, Ltd.     

圆柱尾迹中湍流结构对气体射流混合过程影响的实验研究

本文详细测量了圆柱尾迹中ＣＯ２气体射流的浓度分布，研究了空气来流速度和圆柱直径等参数对射流浓度分布的影响，通过对典型条件下圆柱尾迹端湍流结构参数的测量，讨论了圆柱尾迹的湍流模型参数对气体射流卷混合的影响。     

增强燃烧室内空气紊流降低柴油机油耗,噪声及有害排放物的研究

柴油机燃烧室中空气紊流运动对促进燃烧有重要作用。为改善Ｘ４１０５Ｂ柴油机性能，作采用了高紊流的“Ｑｕａｄｒａｍ”型燃烧室。通过合理选择进气涡流强度、供油速率和供油提前角，取得了良好的效果。不仅改善了燃油经济性，减小了烟度，而且降低了其排放物和噪声。