Investigation of in-cylinder flow patterns in 4 valve S. I. Engine by using single-frame particle tracking velocimetry

The in-cylinder flow field of gasoline engine comprises unsteady compressible turbulent flows caused by the intake port, combustion chamber geometry. Thus, the quantitative analysis of the in-cylinder flow characteristics plays an important role in the improvement of engine performances and the reduction of exhaust emission. In order to obtain the quantitative analysis of the in-cylinder gas flows for a gasoline engine, the single-frame particle tracking velocimetry was developed, which is designed to measure 2-dimensional gas flow field. In this paper, influences of the swirl and tumble intensifying valves on the in-cylinder flow characteristics under the various intake flow conditions were investigated by using this PTV method. Based on the results of experiment, the generation process of swirl and tumble flow in a cylinder during intake stroke was clarified. Its effect on the tumble ratio at the end of compression stroke was also investigated.     

Steady-flow characteristics and its influence on spray for direct injection diesel engine

Flow and spray characteristics are critical factors that affect the performance and exhaust emissions of a direct injection diesel engine. It is well known that the swirl control system is one of the useful ways to improve the fuel consumption and emission reduction rate in a diesel engine. However, until now there have only been a few studies on the effect of flow on spray. Because of this, the relationship between the flow pattern in the cylinder and its influence on the behavior of the spray is in need of investigation. First, in-cylinder flow distributions for 4-valve cylinder head of Dl (Direct Injection) Diesel engine were investigated under steady-state conditions for different SCV (Swirl Control Valve) opening angles using a steady flow rig and 2-D LDV (Laser Doppler Velocimetry). It was found that swirl flow was more dominant than that of tumble in the experimented engine. In addition, the in-cylinder flow was quantified in terms of swirl/tumble ratio and mean flow coefficient. As the SCV opening angle was increased, high swirl ratios more than 3.0 were obtained in the case of SCV -70ΰ and 90ΰ. Second, spray characteristics of the intermittent injection were investigated by a PDA (Phase Doppler Anemometer) system. A Time Dividing Method (TDM) was used to analyze the microscopic spray characteristics. It was found that the atomization characteristics such as velocity and SMD (Sauter Mean Diameter) of the spray were affected by the in-cylinder swirl ratio. As a result, it was concluded that the swirl ratio improves atomization characteristics uniformly.     

Improving fuel efficiency with laser surface textured piston rings

An experimental study is presented to evaluate the effect of partially laser surface textured piston rings on the fuel consumption and exhaust gas composition of a compression-ignition IC engine. Dynamometer tests were performed with a Ford Transit naturally aspirated 2500 cm³ engine at a wide range of engine speeds under near-half-load conditions. A comparison was made between the performance of reference non-textured conventional barrel-shaped rings and optimum partial laser surface texturing (LST) cylindrical-shape rings. It was found that the partial LST piston rings exhibited up to 4% lower fuel consumption, while no traceable change in the exhaust gas composition or smoke level was observed.     

Visualization of liquid fuel behavior in a spark ignition engine during starting and warm-up

The liquid fuel behavior in the intake port and the cylinder during starting and warm-up was visualized through visualization windows using a high speed CCD camera. The videos were taken with the engine firing under cold conditions in the simulated start up process, at 1.000 and 1.200 RPM and intake manifold pressure of 0.5 bar. The variables examined were the injector geometry and injector type (normal and air-assisted). The visualization results show several features of the liquid fuel behavior: 1) backward strip-atomization of the fuel film along the periphery of the intake valves by the valve overlap backflow: 2) forward strip-atomization of the fuel film on the surfaces of the intake system into droplet streams by the intake air flow: 3) film flow which forms significant liquid puddles at the valve surface and at the vicinity of the intake value: and 4) squeezing of the liquid film at the valve lip and seat into large droplets in the valve closing process. Some of the liquid fuel survives combustion into the next cycle. The time evolution of the in-cylinder liquid film is influenced by the injection geometry and port surface temperature. Photographs showing the liquid fuel features and an explanation of the observed phenomena are given in the paper.     

The effect of combustion parameters on the nitric oxide emission in direct injection type diesel engine

This paper presents the investigation of influence factors on the output performance and the reduction of exhaust emission in the direct injection type diesel engine. In this work, the analysis of combustion products and combustion characteristics are investigated by numerical method and experiment under the various engine operating conditions. The combusion performance and exhaust emissions are analyzed in terms of the heat release, cylinder pressure and major exhaust emissions of engine. The accuracy of the prediction versus experimental data and the capability of the heat release, cylinder pressure and all the major exhaust emissions are demonstrated. The results of this study show that the combustion parameters have influence on the combustion processes and the nitric oxide emission in the direct injection type diesel engine. The nitric oxide concentration decreases with the increase of engine speed and the advance of injection timing.     

Piston crevice hydrocarbon oxidation during expansion process in an SI engine

Combustion chamber crevices in SI engines are identified as the largest contributors to the engine-out hydrocarbon emissions. The largest crevice is the piston ring-pack crevice. A numerical simulation method was developed, which would allow to predict and understand the oxidation process of piston crevice hydrocarbons. A computational mesh with a moving grid to represent the piston motion was built and a 4-step oxidation model involving seven species was used. The sixteen coefficients in the rate expressions of 4-step oxidation model are optimized based on the results from a study on the detailed chemical kinetic mechanism of oxidation in the engine combustion chamber. Propane was used as the fuel in order to eliminate oil layer absorption and the liquid fuel effect. Initial conditions of the burned gas temperature and in-cylinder pressure were obtained from the 2-zone cycle simulation model. And the simulation was carried out from the end of combustion to the exhaust valve opening for various engine speeds, loads, equivalence ratios and crevice volumes. The total hydrocarbon (THC) oxidation in the crevice during the expansion stroke was 54.9% at 1500 rpm and 0.4 bar (warmed-up condition). The oxidation rate increased at high loads, high swirl ratios, and near stoichiometric conditions. As the crevice volume increased, the amount of unburned HC left at EVO (Exhaust Valve Opening) increased slightly.     

Numerical analysis of the combustion process in a four-stroke compressed natural gas engine with direct injection system

In this paper, a numerical study to simulate and analyze the combustion process occurred in a compressed natural gas direct injection (CNG-DI) engine by using a multi-dimensional computational fluid dynamics (CFD) code was presented. The investigation was performed on a single cylinder of the 1.6-liter engine running at wide open throttle at a fixed speed of 2000 rpm. The mesh generation was established via an embedded algorithm for moving meshes and boundaries for providing a more accurate transient condition of the operating engine. The combustion process was characterized with the eddy-break-up model of Magnussen for unpremixed or diffusion reaction. The modeling of gaseous fuel injection was described to define the start and end of injection timing. The utilized ignition strategy into the computational mesh was also explained to obtain the real spark ignition timing. The natural gas employed is considered to be 100% methane (CH₄) with three global step reaction scheme. The CFD simulation was started from the intake valves opening until the time before exhaust valves opening. The results of CFD simulation were then compared with the data obtained from the single-cylinder engine experiment and showed a close agreement. For verification purpose, comparison between numerical and experimental work are in the form of average in-cylinder pressure, engine power as well as emission level of CO and NO. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju, Korea, October 16–19, 2007.     

基于数值模拟优化分析的某型汽油机发动机燃烧系统正向开发

文中主要基于喷雾标定的结果进行发动机缸内燃烧系统的正向开发和优化.在喷雾试验数据的基础上建立了喷雾模型,并利用喷雾模型和发动机相关数据进行了缸内燃烧计算,分析了缸内流场和油气混合情况.分析表明:缸内流场方面,在压缩冲程中不同工况下均形成了非常明显的滚流流场,同时滚流比大小的变化存在明显的"双峰"现象,不同工况下均有燃油...     

Precise instrumentation of a diesel single-cylinder research engine

The accuracy of any empirical result is a direct consequence of the quality of experimental setup and the strict control over testing conditions. For internal combustion engines, a large number of parameters that also exhibit complex interdependence may significantly affect the engine performance. Therefore, this work describes the essentials required to establish a high-quality diesel engine research laboratory. A single-cylinder diesel engine is taken as the fundamental building block and the requirements for all essential sub-systems including fuel, intake, exhaust, coolant and exhaust gas recirculation (EGR) are laid out. The measurement and analysis of cylinder pressure, and exhaust gas sampling/conditioning requirements for emission measurement are discussed in detail. The independent control of EGR and intake boost is also highlighted. The measurement and analysis techniques are supported with empirical data from a single-cylinder diesel engine setup. The emphasis is on providing the necessary guidelines for setting up a fully-instrumented diesel engine test laboratory.     

A study on characteristics and control strategies of cold start operation for improvement of harmful exhaust emissions in SI engines

Emission regulations for automobiles have become more stringent and the improvement of emission during cold start has been a major key issue to meet these regulations. Among many kinds of factors that affect cold start operation, ignition timing is crucial to improve emission characteristics due to the influence on exhaust gas temperature. Recent progress in variable valve timing allows optimized valve event strategies under various ranges of engine operating conditions including cold start. This study investigates effects of ignition and exhaust valve timing on exhaust gas temperature, combustion stability and emission characteristics through cold start bench tests of an SI engine. Experimental results show that exhaust valve timings and ignition timings significantly affect exhaust gas temperature and stability of engine operation under cold start condition. Exhaust valve timing also affects CO and NO_x emission due to changes in residual gas fraction of the combustion chamber. Ignition timing mainly affects exhaust gas temperature and HC emission. A control strategy, advanced exhaust valve timing and retarded ignition, is plausible in order to achieve reduction of exhaust emission while maintaining stability under cold start operation of SI engines.     

缸内直喷汽油机冷启动燃烧与排放光学试验研究

结合光学单缸机和激光诱导荧光测量技术对直喷汽油机冷怠速工况缸内油气混合与燃烧过程进行了可视化试验研究。试验采用了屋脊形透明缸套和双侧激光,利用统计图像评估方法得到了缸内混合气浓度和燃烧火焰分布图像,通过缸压传感器和燃烧分析仪对燃烧稳定性进行了分析,采用废气分析仪和光学传感器分别对碳氢和碳烟排放进行了分析评估。研究表明：燃烧稳定时燃油与缸套碰壁是碳氢排放产生的主要原因,碳烟排放则主要由活塞顶部燃油碰壁造成;适当推迟第二次喷油时刻有利于点火时刻火花塞附近稳定浓混合气的形成,继而提高燃烧稳定性,同时减少碳氢排放,过迟喷射会导致碳烟明显增加,过早喷射会造成缸内失火,碳氢排放增加。     

喷射装置导管对大缸径气体燃料发动机缸内混合效果的影响

在喷射装置出口加装导管,将燃气分别导向大缸径多点电喷气体燃料发动机的螺旋进气道和切向进气道,建立了联合喷射装置内部流动区域的发动机瞬态CFD计算模型,分析了导管位置对缸内掺混过程的影响。研究结果表明：对于该切向气道、螺旋气道的组合进气道,进气冲程在缸内靠近缸盖截面上产生了干涉涡流,对于螺旋气道喷射方案,燃气向气缸中心靠近,压缩末了时刻燃气集中在缸盖附近;而对于切向气道喷射方案,燃气冲向活塞顶,压缩末了时刻燃气集中在活塞顶附近。点火时刻的混合效果从优到劣依次为螺旋气道喷射方案、无导管喷射方案、切向气道喷射方案。     

一种新型复合式电磁驱动燃气喷射装置的设计与分析

作为国际远洋船舶的主要动力装置,采用加入气体燃料的低速柴油机在实现节能减排方面拥有巨大潜力。燃气喷射装置作为缸内直喷的核心执行机构,对内燃机燃烧品质和热效率有着重要影响。针对现有电磁驱动喷射装置存在的流量小、驱动力弱等不足,提出一种新型复合式电磁驱动燃气喷射装置。首先,针对驱动机构及阀体提出新的设计思路,通过有限元方法分析了驱动机构的电磁特性及阀体流动特性,验证了设计可行性;其次,建立喷射装置的CFD仿真模型,归纳了流量特性规律;最后,建立试验平台,测试了驱动机构的稳/动态特性。仿真与试验结果表明,新型复合式电磁驱动燃气喷射装置具有高效节能、快响应、高精度的动态特性,对缸内预混特性等具有显著的改善效果。     

直喷汽油机可变滚流进气系统实验研究

建立了可变滚流四气门直喷汽油机光学可视化气道实验台,利用粒子图像测速（PIV）系统对不同进气门开度、不同滚流调节阀工作状态下的缸内气流运动规律进行了实验测试研究。实验结果表明,缸内主要是绕气缸轴线垂直方向旋转的滚流运动;滚流阀开启时,缸内左右两侧分别形成逆时针和顺时针方向的两个大尺度滚流;滚流阀关闭时,进气门侧的气流减弱,排气门侧的流速明显增强,缸内出现了较强的单一顺时针方向滚流运动趋势;进气门开度较小时,改变滚流阀状态对缸内进气流动的影响很微弱。      

The measurement method solving the problems of engine output characteristics caused by change in atmospheric conditions on the principle of the theory of optimal temperature range of exhaust system

All high-performance engines are sensitive to changes in external atmospheric conditions, which are immediately reflected in changes in the engine output characteristics. At best only they effect decreasing of the maximum engine power. However, in a more difficult situation, there is the possibility of excessive detonation combustion process during certain changes in atmospheric conditions. The exhaust system temperature significantly affects the maximum output power and the combustion engine characteristics. With increasing temperature of combustion products in the exhaust system there is an overall reduction in maximum power and its transfer to a higher engine speed because of the length of an exhaust manifold is theoretically shorten. Therefore, to achieve the maximum values of output parameters, it is necessary to ensure an optimal temperature value of the combustion products in the exhaust system. This article also provides optimal temperature range of working temperature as well as it presents a theoretical analysis of the impact for atmospheric conditions in this interval. Based on theoretical results there has been developed a measuring method, which allows to regulate the input amount of the fuel mixture supplied to a cylinder during change in atmospheric conditions and its functionality was experimentally verified.     

An experimental study on the effects of impingement-walls on the spray and combustion characteristics of SIDI CNG

Compressed natural gas (CNG) is regarded as one of the most promising alternative fuels, and maybe the cleanest fuel for the sparkignition (SI) engine. In the SI engine, direct injection (DI) technology can significantly increase the engine volumetric efficiency and decrease the need of throttle valve. During low load and speed conditions, DI allows engine operation with the stratified charge, and the use of extremely lean fuel-air mixture enables relatively higher combustion efficiency. In this study, a combustion chamber with a visualization system is designed. The spray development and combustion propagation processes SIDI CNG were digital recorded. It was found that high injection pressure reduced the ignition probability significantly because of quenching of flame kernel. To improve the ignition probability, three kinds of impingement-walls were designed to help the mixture preparation. It was found that the CNG-air mixture can be easily formed after spray-wall impingement and the ignition probability was also improved. The results of this study can contribute important data for the design and optimization of spark-ignition direct injection (SIDI) CNG engine.     

Cylinder pressure reconstruction based on complex radial basis function networks from vibration and speed signals

Methods to measure and monitor the cylinder pressure in internal combustion engines can contribute to reduced fuel consumption, noise and exhaust emissions. As direct measurements of the cylinder pressure are expensive and not suitable for measurements in vehicles on the road indirect methods which measure cylinder pressure have great potential value. In this paper, a non-linear model based on complex radial basis function (RBF) networks is proposed for the reconstruction of in-cylinder pressure pulse waveforms. Input to the network is the Fourier transforms of both engine structure vibration and crankshaft speed fluctuation. The primary reason for the use of Fourier transforms is that different frequency regions of the signals are used for the reconstruction process. This approach also makes it easier to reduce the amount of information that is used as input to the RBF network. The complex RBF network was applied to measurements from a 6-cylinder ethanol powered diesel engine over a wide range of running conditions. Prediction accuracy was validated by comparing a number of parameters between the measured and predicted cylinder pressure waveform such as maximum pressure, maximum rate of pressure rise and indicated mean effective pressure. The performance of the network was also evaluated for a number of untrained running conditions that differ both in speed and load from the trained ones. The results for the validation set were comparable to the trained conditions.     

Effect of water induction on the performance and exhaust emissions in a diesel engine (II)

This study was to investigate the effects of water induction through the air intake system on the characteristics of combustion and exhaust emissions in an IDI diesel engine. The fuel injection timing was also controlled to investigate a method for the simultaneous reduction of smoke and NOx when water was injected into the combustion chamber. The formation of NOx was significantly suppressed by decreasing the gas peak temperature during the initial combustion process because the water played a role as a heat sink during evaporating in the combustion chamber, while the smoke was slightly increased with increased water amount. Also, NOx emission was significantly decreased with increase in water amount. A simultaneous reduction in smoke and NOx emissions was obtained when water was injected into the combustion chamber by retarding more 2°CA of the fuel injection timing than without water injection.     

分形维数在内燃机振动诊断中的应用

将分形理论引入内燃机的振动诊断中,根据内燃机的配气定时,着重研究了缸盖振动信号中对应燃烧段的数据,计算其关联维数,将关联维数用于刻划内燃机缸盖在气门不同状态时表现的非线性行为,从而进行故障诊断与分类。结果表明,当气门在不同状态时,缺盖振动信号中对应燃烧段数据的关联维数是不同的,可以将其作为判断气门漏气的一个诊断特征量。     

Phenomenological combustion modeling of a direct injection diesel engine with in-cylinder flow effects

A cycle simulation program is developed and its predictions are compared with the test bed measurements of a direct injection (DI) diesel engine. It is based on the mass and energy conservation equations with phenomenological models for diesel combustion. Two modeling approaches for combustion have been tested; a multi-zone model by Hiroyasu et al (1976) and the other one coupled with an in-cylinder flow model. The results of the two combustion models are compared with the measured imep, pressure trace and NOx and soot emissions over a range of the engine loads and speeds. A parametric study is performed for the fuel injection timing and pressure, the swirl ratio, and the squish area. The calculation results agree with the measured data, and with intuitive understanding of the general operating characteristics of a DI diesel engine.