Velocity measurement inside a motored internal combustion engine using three-component laser Doppler anemometry

A three-component laser Doppler anemometry (LDA) system has been employed to investigate the structure of the flow inside the cylinder of a motored internal combustion engine. This model engine was reasonably representative of a typical, single cylinder, spark ignition engine although it did not permit firing. It was equipped with overhead valve gear and optical access was provided in the top and side walls of the cylinder. A principal objective was to study the influence of the inlet port design on the flow within the cylinder during the induction and compression strokes of the engine. Here, it can be noted that results obtained in an unfired engine are believed to be representative of the flow behaviour before combustion occurs in a fired engine (see P.O. Witze, Measurements of the spatial distribution and engine speed dependence of turbulent air motion in an i.c. engine, SAE Paper No. 770220, 1977; Witze, Sandia Laboratory Energy Report, SAND 79-8685, Sandia Laboratories, USA, 1979). Experimental data presented for an inclined inlet port configuration reveal the complex three-dimensional nature of the flow inside the model engine cylinder. Not surprisingly, the results also show that the inclined inlet port created flow conditions more favourable to mixing in the cylinder. Specifically, the inclined inlet flow was found to generate a region with a relatively high shear and strong recirculation zones in the cylinder. Inclining the inlet port also produced a more nearly homogeneous flow structure at top dead centre during the compression stroke. The paper identifies the special difficulties encountered in making the LDA measurements. The experimental findings are examined and the problems that arise in presenting time-varying three-dimensional data of this type are discussed. Finally, the future potential of this experimental approach is explored.     

内燃机气缸内三维气体流场的数值模拟

从计算机模拟角度研究发动机缸内气体流动的全貌以探求合理组织气流的途径是当前国内外研究的重要项目，本文提出一个基于有限体积方法的方法，并应用于发动机缸内气流的数值模拟，最后与热线风速仪测量值进行了比较，给出了结果及分析。     

Measuring wave dynamics in IC engine intake systems

Wave dynamics in the intake system are known to strongly influence the performance of naturally aspirated internal combustion (IC) engines. Detailed measurements of the wave dynamics are required to optimize the performance of an engine, to validate the results of an engine performance simulation or to better understand the physics of the intake system. Five different methods for making such measurements are discussed in this paper. Four are based on different forms of pressure measurement and one uses hot-wire anemometry. The different methods are investigated by using results obtained on a single cylinder research engine. The different methods are used to produce measurements of fluctuating pressure and velocity as well as the specific acoustic impedance ratio of the intake pipe. Both time and frequency domain results are considered. The conclusion is that no single method is perfect or indeed universally applicable to all situations and in a typical investigation of wave action more than one method is likely to be used. The combined use of two methods, wave decomposition and an unusual bi-directional pitot-static tube, seems to offer a robust reliable and useful strategy for measuring wave dynamics in the intake pipe that should prove successful on most IC engines.     

隔离段激波串流场特征的试验研究进展

高超声速推进技术是国际前沿研究, 其中双模态超燃冲压发动机的发展受到极大关注. 作为超燃冲压发动机的重要部件, 隔离段对发动机的性能和高超声速飞行的实现至关重要, 其中所涉及的流动机理问题也极为复杂. 自从高超声速飞行的概念被提出和论证以来, 相关的理论、试验和仿真研究不断取得进展, 但是对其中的机理问题研究仍有待进一步深入. 本文将从试验研究的角度回顾并综述近年来超燃冲压发动机隔离段的研究进展, 结合精细流动测试技术(Nano-tracer Planar Laser Scattering, NPLS)的发展分析了隔离段流场特征, 包括了激波串流场复杂的三维时空结构特点、湍流特性、非线性迟滞运动、不启动流场特征以及激波前缘检测等. 从风洞设备、隔离段设计、测试技术等方面对隔离段的试验研究进行了分类比较和论述, 对今后隔离段试验研究提出了建议.     

Quantitative visualization of high-speed 3D turbulent flow structures using holographic interferometric tomography

Using holographic interferometry the three-dimensional structure of unsteady and large-scale motions within subsonic and transonic turbulent jet flows has been studied. The instantaneous 3D flow structure is obtained by tomographic reconstruction techniques from quantitative phase maps recorded using a rapid-switching, double reference beam, double pulse laser system. The reconstruction of the jets studied here reveal a three-dimensional nature of the flow. In particular an increasing complexity can be seen in the turbulence as the flow progresses from the jet nozzle. Furthermore, a coherent three-dimensional, possibly rotating, structure can be seen to exist within these jets. The type of flow features illustrated here are not just of fundamental importance for understanding the behavior of free jet flows, but are also common to a number of industrial applications, ranging from the combustion flow within an IC engine to the transonic flow through the stages of a gas turbine.     

Evaluation of the flame propagation within an SI engine using flame imaging and LES

This work shows experiments and simulations of the fired operation of a spark ignition engine with port-fuelled injection. The test rig considered is an optically accessible single cylinder engine specifically designed at TU Darmstadt for the detailed investigation of in-cylinder processes and model validation. The engine was operated under lean conditions using iso-octane as a substitute for gasoline. Experiments have been conducted to provide a sound database of the combustion process. A planar flame imaging technique has been applied within the swirl- and tumble-planes to provide statistical information on the combustion process to complement a pressure-based comparison between simulation and experiments. This data is then analysed and used to assess the large eddy simulation performed within this work. For the simulation, the engine code KIVA has been extended by the dynamically thickened flame model combined with chemistry reduction by means of pressure dependent tabulation. Sixty cycles have been simulated to perform a statistical evaluation. Based on a detailed comparison with the experimental data, a systematic study has been conducted to obtain insight into the most crucial modelling uncertainties.     

进气加入CO2对直喷式柴油机燃烧的影响

在直喷式柴油机上研究了进气加入CO2气体对其燃烧特性以及发动机性能和排放品质的影响.研究结果表明,进气加入CO2,柴油机的混合气形成过程几乎不受CO2气体加入量的影响,主要反映在着火延迟期随着CO2加入量的增加而变长,燃烧持续期缩短,燃烧最高温度降低.同时导致柴油机的最大爆发压力和压力升高率降低,并且其出现的位置后移,充气效率下降,排气温度上升.加入CO2后,NOx排放有较大下降,HC、CO稍有增加,烟度受到的影响不大.     

A high-speed all-digital technique for cycle-resolved 2-D flow measurement and flow visualisation within SI engine cylinders

Particle image velocimetry (PIV) is now a well-established planar flow measurement technique for the study of in-cylinder flow fields in internal combustion engines. Here the authors describe a turnkey, high-speed digital imaging system that provides combined real-time flow visualisation and rapidly processed PIV data in an industrial optical research engine facility. The system is based on commercially available, high-speed imaging and laser technology and conventional digital cross-correlation processing to provide cycle-resolved PIV data and flow visualisation within timescales appropriate for engine development. A simple variation on the synchronisation scheme also allows the acquisition of tens to thousands of flow visualisation sequences and PIV maps at the same crank angle, thus giving the potential for the study of cycle-to-cycle flow variability and its effect on combustion stability in a suitably instrumented optical engine. The technique may also find applications in other unsteady or oscillatory flows of importance in aerodynamics, acoustics, mixing, and heat transfer.     

6110柴油机进气过程流动的多维瞬态数值模拟研究

柴油机进气过程中气体流动是强瞬变的非定常三维湍流运动,直接影响到充气效率、缸内气流状态及进气道和缸内壁面换热,因而也影响到燃油雾化、燃烧及有害废气生成等,对柴油机的动力性、经济性起着重要作用。因此,本文利用大型通用CFD软件STAR-CD及ES-ICE对6110柴油机进气过程的气体流动进行多维瞬态数值模拟研究,通过计算可以得到不同时刻进气道和缸内流场分布,为柴油机进气系统的优化设计提供重要的理论依据。     

柴油引燃天然气的双燃料燃烧机理的研究

本文介绍在一台光学发动机上,利用高速数字摄像和数据采集技术,对柴油引燃天然气双燃料发动机的着火、火焰传播、气缸内压力、压力升高率等变化规律进行的研究。结果表明,采用双燃料的燃烧方式具有明显的多点着火型的预混燃烧特点,与采用纯柴油的燃烧方式相比,燃烧持续期短、产生的碳烟少,但爆发压力高、压力升高率大。     

The structure of the high-pressure gas jet from a spark plug fuel injector for direct fuel injection

Abstract  

A spark plug fuel injector (SPFI), which is a combination of a fuel injector and a spark plug was developed with the aim to convert any gasoline port injection spark ignition engine to gaseous fuel direct injection (Mohamad in Development of a spark plug fuel injector for direct injection of methane in spark ignition engine. PhD thesis, Cranfield University, 2006). A direct fuel injector is combined with a spark plug using specially fabricated bracket connected to a fuel pipe and a fuel path running along the periphery of a spark plug body to deliver the injected fuel to the combustion chamber. The injection nozzle of SPFI is significantly bigger than normal direct fuel injector nozzles. Therefore, it is important to understand the effect of such a configuration on the injection process and subsequently the air–fuel mixing behaviour inside the combustion chamber. The flow was visualized using the planar laser-induced fluorescent technique. For safety reasons, nitrogen was used as fuel substitute. Nitrogen at 50, 60 and 80 bar pressure was seeded with acetone as a flow tracer and injected into a bomb containing pressurised nitrogen. Bomb pressure was varied to simulate the pressure inside combustion cylinder during the compression stroke where actual injections in engine experiments will take place. The shape and depth of tip penetration of the gas jet were measured. Results show that the gas jet follows the behaviour suggested by vortex ball model (Turner in Mechanics 13:356–369, 1962). The cone angle and the maximum jet width of the fully developed gas jets from the SPFI injection are 23° and 25 mm, respectively regardless of the injection pressures. The penetration lengths of the fully developed jets are between 90 and 100 mm at 8–14 ms after the start of injection, depending on the bomb and injection pressure. Jet penetration is directly proportional to the injection pressure but inversely proportional to the cylinder or bomb pressure. The penetration lengths indicate that sufficient distance should be travelled by the gas jet for satisfactory air–fuel mixing in the engine.     

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.     

Chaotic mixing generated by acoustic streaming

The acoustic mixer presented in this paper is a closed cylinder containing chemical solutions. The ultrasound was generated in a water bath outside of the cylinder. The mixing efficiency was measured by using a laser-photodiode system and by mixing iodine and sodium thiosulfate. Iodine solution has a light brown color which becomes transparent if the solution is mixed with sodium thiosulfate. The unmixed regions of the solution in the container remain dark. Starch was used to make the solution darker. Considering the relative position between the cylinder and the transducer, it was shown that displacements parallel to the axes of the streaming have little effect on the mixing speed. Indeed, the distance of the cylinder from the center of the streaming is more important to obtain ideal mixing performances. The frequency and size of the transducers has been investigated too and little effect was found. In contrast, the wave amplitude seems to be the biggest factor in obtaining rapid mixing.     

Acoustic properties of heated twin jets

A thorough experimental study of the noise characteristics of twin jets is presented in this paper. Twin round jets are investigated at typical jet engine conditions: that is, with heated high velocity flow. By varying the nozzle to nozzle spacing, it is possible to discriminate between the effects of turbulent mixing and acoustic shielding. As a result of this investigation, it was established that the turbulent mixing effects (both interaction noise generation and mixing suppression) occur for closely spaced nozzles. While acoustic shielding occurs at all nozzle spacings, it plays the dominant role at wide nozzle spacings. The levels of this acoustic shielding afforded by an adjacent jet can be sufficient to cause a nearly complete masking of the noise of the shielded jet. A significant discovery of this investigation was the importance of the layer of cooler, slower moving ambient air that exists between the twin jet plumes. This inter-jet layer causes acoustic refraction and reflection, and as the nozzle separation increases, the layer extends to shield more of the jet noise sources.     

A Critical Review on Physical Vapor Deposition Coatings Applied on Different Engine Components

Friction and wear in different engine components have crucial effects on the engine performance, combustion efficiency, oil consumption and lifetime of the internal combustion (IC) engine. Under certain loads, speeds, and temperatures, the metallic components of the IC engine, especially the piston and valve system suffer from a higher friction. Thin film coating is one of the novel techniques to reduce the frictional forces and improve the mechanical properties of engine components. Due to some versatile tribological properties, increasing attention has been paid to the physical vapor deposition (PVD) technology in the recent decade to deposit thin film coating on engine components. This article presents a comprehensive literature review on thin film coatings for IC engine components deposited by PVD technique. Issues related to tribological properties (wear and coefficient of friction) and mechanical properties (hardness and roughness) are also highlighted. Scientific improvements are presented in the light of literature. It is revealed that PVD coating is significantly effective on wear resistance, scuffling resistance, surface roughness, and friction of the components in IC engine. Laboratory test and data from actual service so far suggest that the plasma-activated electron beam evaporation coating is perhaps one of the best choices for smooth surface finishing with improved mechanical and tribological properties. However, there are still some problems in its practical usage. This compressive review paper presents the major shortcomings of PVD coatings on IC engine components and the possible solutions if any. Finally, a number of issues have been reported which need to be encountered for further studies.     

Absorption of sound at a surface exposed to flow and temperature gradients

In noise abatement using porous or fibrous materials, accurate determination of the surface impedance representing the absorber is decisive for simulation quality. The presence of grazing flow and non-homogeneous ambient temperature influence the reaction of the absorber and may suitably be included in a modified “effective” surface impedance. In this paper, this approach is applied to a generic case representative for the engine bay of a heavy truck, where porous shields suppress the radiated noise, e.g. during a pass-by noise test. The change in the absorption is determined numerically by solving the wave propagation through a layer of varying temperature and flow adjacent to the impedance surface for different angles of incidence. The study shows significant impact of both flow and temperature, especially for materials with low absorption. The diffuse field absorption coefficient is also derived and although the effect is less pronounced in this case, it is still important in lower frequencies and in the frequency range typical for IC engine noise. The proposed numerical method is shown to be accurate and efficient for determination of the effective impedance and moreover not limited to thin boundary layers.     

Influence of the in-cylinder flow on cycle-to-cycle variations in lean combustion DISI engines measured by high-speed scanning-PIV

In this study, the influence of the three-dimensional (3D) in-cylinder flow on engine's cycle-to-cycle variations (CCV) in a spray-guided direct-injection spark-ignition engine is investigated. The engine is operated at homogeneous lean air–fuel mixture which enhances the sensitivity to CCV due to reduced laminar flame speed. To compensate this, intake velocity is increased by a tumble-flap (TF) in the intake-port. To address the 3D-nature of the temporal evolution of the instantaneous in-cylinder flow for different TF-positions, time-resolved scanning particle image velocimetry (Scanning-PIV) is applied to the engine. The required scan-frequency is provided by an acousto-optical-deflector (AOD) to measure the flow field quasi-simultaneously in the central tumble-plane and both mid-valve-planes. The three planes are 18?mm displaced from each other to capture the variability of the large-scale tumble vortex. The in-cylinder flow measurements are combined with combustion analyses by the in-cylinder pressure-trace and the detection of the location of ignition through the evaluation of the luminous spark-plasma. A correlation-map analysis is conducted to identify coherent flow features responsible for CCV of the combustion parameters. This reveals a strong dependency of the spark position to variations of an upward directed flow pointing onto the spark plug. The variations of the upward flow are due to strong CCV of the bended tumble-axis position. An increased tumble motion caused by the TF results in favorable flow conditions by stabilizing the tumble-axis in the middle of the cylinder which decreases the CCV of the spark position significantly. Further correlation analysis including the combustion process exhibits that flow-structures moving the spark and early flame kernel towards the cylinder center reduces the crank angle of 5% heat release and the combustion duration considerably.     

A hybrid approach for aeroacoustic analysis of the engine exhaust system

This paper presents a new hybrid approach for prediction of noise radiation from engine exhaust systems. It couples the time domain analysis of the engine and the frequency domain analysis of the muffler, and has the advantages of both. In this approach, cylinder/cavity is analyzed in the time domain to calculate the exhaust mass flux history at the exhaust valve by means of the method of characteristics, avoiding the tedious procedure of interpolation at every mesh point and solving a number of equations simultaneously at every junction. This is done by making use of an interrelationship between progressive wave variables of the linear acoustic theory and those of the method of characteristics. In this approach, nonlinear propagation in the exhaust pipe is neglected and free expansion is assumed at the radiation end of the exhaust pipe. In the case of a muffler proper, expansion from the exhaust pipe into the first chamber is assumed to be a free expansion. Various results of this approach are compared with those of the method of characteristics and the classical acoustic theory, and various peaks and troughs in insertion loss curves are analytically validated.     

Particle image velocimetry analysis of IC engine in-cylinder flows

This paper discusses the use of particle image velocimetry for measuring in-cylinder flows in multi-valve IC engines. The techniques and their limitations are discussed with special reference to the study of large-scale flow structures in a four valve optical IC engine exhibiting significant barrel swirl. Examples of velocity vector maps derived by digital autocorrelation are presented for a range of crank angles through the induction and compression strokes from both horizontal and vertical measurement planes. The evident strengths and limitations of the current technique for in-cylinder applications are discussed with respect to spatial resolution, velocity gradients and dynamic range. Recent developments for overcoming the limitations are also reviewed.