Combustion process in a spark ignition engine: analysis of cyclic peak pressure and peak pressure angle oscillations

In this paper we analyze the cycle-to-cycle variations of peak pressure p _max and peak pressure angle α _pmax in a four-cylinder spark ignition engine. We examine the experimental time series of p _max and α _pmax for three different spark advance angles. Using standard statistical techniques such as return maps and histograms we show that depending on the spark advance angle, there are significant differences in the fluctuations of p _max and α _pmax . We also calculate the multiscale entropy of the various time series to estimate the effect of randomness in these fluctuations. Finally, we explain how the information on both p _max and α _pmax can be used to develop optimal strategies for controlling the combustion process and improving engine performance.     

Development of a high-speed UV particle image velocimetry technique and application for measurements in internal combustion engines

A flexible, high-frame rate particle image velocimetry technique that can be applied to operating internal combustion engines in highly luminous combustion situations was developed. Two high-repetition rate diode-pumped Nd:YAG lasers operated at 355 nm and a CMOS camera were used to devise a system that allowed measurements of velocity fields near the spark plug in a firing engine at a rate of 6 kHz for 500 consecutive cycles. The 6 kHz acquisition rate enables recording one velocity field every other crank angle at 2,000 RPM engine speed. Sample results such as individual and average flow fields and kinetic energy evolutions are presented.     

Large Eddy Simulation of Spark Ignition in a Gas Turbine Combustor

Ignition in an aircraft gas turbine combustion chamber is simulated using Large Eddy Simulation (LES) in conjunction with the filtered probability density function (pdf) equation approach, which is solved using the Eulerian stochastic field method. The LES-pdf methodology is used for both dispersed (liquid) and gas phases. The liquid phase is described using a Lagrangian formulation whilst an Eulerian approach is employed for the gas phase. The spark energy deposition was mimicked by a distributed energy source term added to the enthalpy equation. Unsuccessful and successful ignition sequences have been simulated and the results suggest that spark ‘size’ is an important parameter in the ignition of kerosene fuelled combustion chambers.     

汽油机燃烧室内温度场测量的激光剪切干涉法

采用激光剪切干涉法测量了汽油机燃烧室内的温度场,并分析了剪切干涉法测温的基本原理,推导出利用干涉条纹图求解温度分布的关系式。在一台二冲程火花点火发动机上设置石英窗和信号同步系统,建立了适合高速摄影的激光剪切干涉测量装置。通过改变剪切干涉量,测取发动机燃烧室内干涉条纹图,从而获得缸内燃烧的二维温度场。结果表明,激光剪切干涉法抗振性强,光路简单可靠,可以进行高速摄像,是研究内燃机燃烧过程的有效方法。从温度场可以看出,燃烧过程中缸内大致可分为三个区,即已燃区、未燃区和燃烧区,具有不同的温度分布和温度梯度。燃烧区温度最高,温度梯度大;已燃区温度次之,梯度较小;未燃区温度最低,但梯度较大。     

Ablation combustion of secondary powder explosives

The explosive transformation in a passive charge initiated by an air shock wave was studied using synchrotron diagnostics of density. It was found that in the passive charge, a compression wave capable of forming effective hot spots does not arise and classical initiation conditions do not occur. The development of the reaction can be attributed to the ablation combustion observed in studies of the initiation of secondary powder explosives by a spark and gaseous detonation.     

Numerical Evaluation of Combustion Regimes in a GDI Engine

There is significant interest in the gasoline direct-injection engine due to its potential for improvements in fuel consumption but it still remains an area of active research due to a number of challenges including the effect of cycle-by-cycle variations. The current paper presents the use of a 3D-CFD model using both the RANS and LES turbulence modelling approaches, and a Lagrangian DDM to model an early fuel injection event, to evaluate the regimes of combustion in a gasoline direct-injection engine. The velocity fluctuations were investigated as an average value across the cylinder and in the region between the spark plug electrodes. The velocity fluctuations near the spark plug electrodes were seen to be of lower magnitude than the globally averaged fluctuations but exhibited higher levels of cyclic variation due to the influence of the spark plug electrode and the pent-roof geometry on the in-cylinder flow field. Differences in the predicted flame structure due to differences in the predicted velocity fluctuations between RANS and LES modelling approaches were seen as a consequence of the inherently higher dissipation levels present in the RANS methodology. The increased cyclic variation in velocity fluctuations near the spark plug electrodes in the LES predictions suggested significant variation in the relative strength of the in-cylinder turbulence and that may subsequently result in a thickening of the propagating flame front from cycle-to-cycle in this region. Throughout this paper, the numerical results were validated against published experimental data of the same engine geometry under investigation.     

Investigations into the effect of LDV seed particles on the operating characteristics of a spark ignition engine

 LDV measurements are commonly made in spark ignition engines to investigate the interaction between the flow field and the combustion process. To achieve high LDV data rates relatively large quantities of seed particles must be introduced into the engine intake flow. Based on the measurement of the characteristic engine operating parameters, it was determined that the introduction of TiO₂ seed particles into an optical L-head research engine fuelled by natural gas at stoichiometric and lean conditions did not significantly influence the combustion process. Received: 11 March 1998/Accepted: 4 November 1998     

Comparison of Combustion Models and Assessment of Their Applicability to the Simulation of Premixed Turbulent Combustion in IC-Engines

In order to simulate the turbulent combustion process occurring in spark-ignition (IC) engines, it is necessary to provide suitable and numerically economical models, the latter being particularly important in the application to industrial problems. Moreover, these models must deliver sufficiently accurate results for the unsteady operation of spark combustion engines, concerning variable geometries, temperatures, pressures and charge development in different configurations. In this work different turbulent combustion models for premixed hydrocarbon combustion are compared with respect to their ability to accurately predict the propagation of turbulent perfectly premixed flames. As a first configuration a cylinder of constant volume was studied. Transient calculations were used to simulate the propagation of the turbulent flame and to evaluate the resulting turbulent burning velocity. These calculations were performed for a perfect mixture of air and hydrocarbons at stoichiometric mixture and different initial conditions concerning pressure, temperature and turbulence intensity. As a second configuration a stationary turbulent bunsen-type flame with methane fuel was used to validate the turbulent combustion model of [Lindstedt and Vaos, Combust. Flame 116 (1999) 461] at different pressures. Calculated results were then compared to experimental data of [Kobayashi, Tamura, Maruta and Niioka. In: Proceedings of the 26th Symposium on Combustion, 1996, p. 389] and show excellent agreement for the turbulent burning velocity at several pressure levels using only a single set of model parameters.     

Investigation of Two-Fluid Methods for Large Eddy Simulation of Spray Combustion in Gas Turbines

An extension of the large eddy simulation (LES) technique to two-phase reacting flows, required to capture and predict the behavior of industrial burners, is presented. While most efforts reported in the literature to construct LES solvers for two-phase flow focus on Euler–Lagrange formulation, the present work explores a different solution (‘two-fluid’ approach) where an Eulerian formulation is used for the liquid phase and coupled with the LES solver of the gas phase. The equations used for each phase and the coupling terms are presented before describing validation in two simple cases which gather some of the specificities of real combustion chamber: (1) a one-dimensional laminar JP10/air flame and (2) a non-reacting swirled flow where solid particles disperse (Sommerfeld and Qiu, Int. J. Multiphase Flow 19(6):1093–1127, 1993). After these validations, the LES tool is applied to a realistic aircraft combustion chamber to study both a steady flame regime and an ignition sequence by a spark. Results bring new insights into the physics of these complex flames and demonstrate the capabilities of two-fluid LES.     

High-speed imaging for direct-injection gasoline engine research and development

In recent years, new laser and camera technology have enabled the development of high-speed imaging diagnostics for measurements at frame rates commensurate with the time scales of turbulent mixing, combustion, and emission formation in internal combustion engines. The ability to study the evolution of in-cylinder flow, fuel/air mixing, ignition, and combustion within individual cycles and for many consecutive cycles provides new insights into the physics and chemistry of internal combustion engine performance. Data for model development and device development are obtained with unprecedented access to the identification of random events such as cycle to cycle variation and ignition instabilities. This paper summarizes high-speed diagnostics developments with a focus on application to spark-ignition direct-injection gasoline engines. A range of optical techniques is described along with examples of applications in research and near-production engines. Measurements of in-cylinder velocities were conducted with particle image velocimetry. The spray evolution was followed with Mie scattering. Quantitative fuel distributions were recorded with laser-induced fluorescence. Fuel impingement on surfaces was quantified with refractive index matching. Combined velocity and fuel measurements were used to study ignition reliability. Chemiluminescence techniques provided insights into the evolution of the spark plasma as well as the growing flame kernel. Chemiluminescence and black body radiation imaging yielded insights into the formation and oxidation of soot.     

The development and application of a fast-response DC-coupled flame ionization current sensor

The principles of the design of a fast-response DC-coupled ionisation probe and associated electronic circuit are described for the measurement of the mean and fluctuating components of the ion concentration in the reaction zones of stationary and transient flames. The performance of the ionisation probe is evaluated by bench tests and with measurements of ion current mean and fluctuating levels in laminar and turbulent premixed flames and in the combustion chamber of a spark ignition engine. The results demonstrate the wide frequency bandwidth, good spatial resolution and electronic noise immunity of the ionisation probe, making it suitable for a host of combustion applications.     

Cyclic variations of fuel-droplet distribution during the early intake stroke of a lean-burn stratified-charge spark-ignition engine

Lean-burn spark-ignition engines exhibit higher efficiency and lower specific emissions in comparison with stoichiometrically charged engines. However, as the air-to-fuel (A/F) ratio of the mixture is made leaner than stoichiometric, cycle-by-cycle variations in the early stages of in-cylinder combustion, and subsequent indicated mean effective pressure (IMEP), become more pronounced and limit the range of lean-burn operation. Viable lean-burn engines promote charge stratification, the mixture near the spark plug being richer than the cylinder volume averaged value. Recent work has shown that cycle-by-cycle variations in the early stages of combustion in a stratified-charge engine can be associated with variations in both the local value of A/F ratio near the spark plug around ignition timing, as well as in the volume averaged value of the A/F ratio. The objective of the current work was to identify possible sources of such variability in A/F ratio by studying the in-cylinder field of fuel-droplet distribution during the early intake stroke. This field was visualised in an optical single-cylinder 4-valve pentroof-type spark-ignition engine by means of laser-sheet illumination in planes parallel to the cylinder head gasket 6 and 10 mm below the spark plug. The engine was run with port-injected isooctane at 1500 rpm with 30% volumetric efficiency and air-to-fuel ratio corresponding to both stoichiometric firing (A/F=15, Φ =1.0) and mixture strength close to the lean limit of stable operation (A/F=22, Φ =0.68). Images of Mie intensity scattered by the cloud of fuel droplets were acquired on a cycle-by-cycle basis. These were studied in order to establish possible correlations between the cyclic variations in size, location and scattered-light intensity of the cloud of droplets with the respective variations in IMEP. Because of the low level of Mie intensity scattered by the droplets and because of problems related to elastic scattering on the walls of the combustion chamber, as well as problems related to engine “rocking” at the operating conditions close to the misfire limit, the acquired images were processed for background subtraction by using a PIV-based data correction algorithm. After this processing, the arrival and leaving timings of fuel droplets into the illuminated plane were found not to vary significantly on a cycle-by-cycle basis but the recorded cycle-by-cycle variations in Mie intensity suggested that the amount of fuel in the cylinder could have been 6–26% greater for the “strong” cycles with IMEP 115% higher than the average IMEP, than the ones imaged for “weak” cycles at less than 85% the average IMEP. This would correspond to a maximum cyclic variability in the in-cylinder equivalence ratio Φ of the order of 0.17.     

Magnetic Field Influence on the Gas Detonation Induced by Spark Discharge

The present paper describes the influence of magnetic field on the spark discharge utilized for initialization of detonation. The method of schlieren time-based scanning shows the increase of shock wave velocity in the case when magnetic field was applied to the area of electrical discharge in the air. The critical energy values are obtained for a direct initialization of detonation in hydrogen–air and hexane–air mixtures. Magnetic field has a significant influence on the deflagration–combustion transition in both mixtures at the critical energy values. Pressure and velocity of the shock front were measured by ICP pressure transducers, flame front was recorded by photo-diodes. Two cases were studied experimentally: external magnetic field is produced by inductance coils connected to capacitor; own magnetic field is induced directly by discharge current in the cables positioned in special way.     

10m3爆炸罐中甲烷燃烧爆炸发展过程

在大型多相混合物爆炸实验系统(10m3爆炸罐)中对甲烷/空气混合物在40J电火花点火条件下爆炸发展过程进行了实验和数值模拟研究.采用中心电火花点火,并在距点火点不同距离处设置4个压力传感器.得到下列实验结果:甲烷爆炸上、下限分别为13.9%、4.75%;甲烷浓度为9.5%的爆炸特性参数随距离变化规律;不同甲烷浓度对超压...     

氢氧燃烧及爆轰驱动激波管

分析并观察了沿驱动段轴向分布多火塞燃烧驱动段的性能．提出主膜处同一管截面均匀分布三火花塞引燃的点火方法．用这种点火方法驱动产生的入射激波强度重复性较高,激波后气流速度、温度和压力的定常性亦大大改善,可满足气动试验实际要求．提出在驱动段尾端串接卸爆段来消除爆轰波反射高压,从而可使反向爆轰驱动段用来产生高焓高密度试验气流．这种反向爆轰驱动产生的入射激波重复性高,激波衰减弱．在主膜处的收缩段产生的反射波可缓解爆轰波后跟随的稀疏波的不利影响,从而使前向爆轰驱动具有实用性．在产生的入射激波强度相同条件下,前向爆轰驱动所需的爆轰驱动段可爆混合气初始压力可较反向爆轰低近一个量级．     

倾斜壁面浸润性梯度驱动液滴运动过程的格子Boltzmann模型研究

基于介观模型的多组分伪势格子Boltzmann方法,模拟了倾斜壁面浸润性梯度驱动液滴的运动过程,研究了壁面浸润性梯度、壁面倾斜角度对液滴运动过程的影响．结果表明,对于一定倾斜角度的壁面,当壁面上浸润性梯度足够大时,液滴能够克服重力的作用实现“爬坡”;液滴在运动过程中,其前进及后退接触角与当地静态接触角间存在差值;增大壁面浸润性梯度时,液滴能够获得更快的加速,并且前进及后退接触角与当地静态接触角之间的差值也随之增大;增大壁面倾斜角度时,液滴的运动受到阻碍,前进及后退接触角与当地静态接触角的差值小幅减小．     

等离子体发生器放电参数对推进剂燃烧特性的影响

揭示了电热化学炮所用的等离子体发生器初始放电参数对推进剂燃烧特性的影响规律。实验主要在密闭药室里进行 ,研究了等离子体发生器中毛细管初始几何尺寸以及输入电能发生变化时 ,推进剂的燃烧行为发生的变化规律。研究结果表明 ,推进剂的燃烧行为对等离子体发生器初始放电参数有较强的依赖性。     

探索发展激波风洞爆轰驱动技术

发现了燃烧驱动激波管中入射激波马赫数异常升高的起因. 实验显示爆轰驱动能力强于燃烧驱动, 从而推动爆轰驱动技术的发展. 采用卸爆管消除爆轰波反射高压以及双爆轰驱动段全部消除爆轰波后的Taylor稀疏波, 使反向和前向爆轰驱动模式具有实用价值. 反向爆轰驱动技术还成功用来延长激波风洞试验时间.      

激波诱导燃烧流场模拟的无网格算法

发展了基于无网格方法的激波诱导燃烧流场数值模拟算法. 该算法采用二维多组分Euler方程,在点云离散的基础上采用曲面逼近计算空间导数,引入多组分HLLC （Harten-Lax-van Leer-contact） 格式计算无黏通量,运用四阶Runge-Kutta 法进行时间显式推进,化学动力学采用有限速率反应模型. 对不同预混气体中的激波诱导燃烧流场进行了数值模拟,结果同相关文献吻合较好,验证了算法的正确性.