柴油发动机缸内温度测量新技术研究

为测量柴油发动机缸内三维温度场,提出应用激光测试新技术,该技术通过对发动机缸体打孔,使激光进入缸体内部,利用激光的特性测试出发动机缸内湍流火焰瞬时温度.分析比较实验与计算结果,为发动机设计人员提供了新的测试技术思路.     

增压汽油机曲轴疲劳强度优化设计

针对在某1.4L发动机基础上开发1.4L增压发动机需要更高强度曲轴的问题,对原机型曲轴进行了优化设计以满足增压发动机设计需求.在材料方面用更高强度的锻钢代替了球墨铸铁;在工艺方面将曲轴圆角滚压压力由6000N提高到了7000 N;在结构方面优化了曲轴平衡重结构,达到了减重增强的效果,使优化后曲轴重量比原曲轴轻了0.04 kg.基于GME L-6C-1试验标准,通过曲轴弯曲疲劳试验的对比验证,优化后曲轴疲劳强度从645 N·m提高到801 N·m,提高了24％.研究结果表明,优化设计后的曲轴完全满足1.4L增压发动机的要求.     

A study on the measurement of temperature and soot in a constant-volume chamber and a visualized diesel engine using the two-color method

In this study, the measurements of soot and temperature were used to investigate the turbulent diesel diffusion flame in a constant-volume chamber and a visualized direct injection (D.I.) diesel engine using the two-color method and a high-speed camera. Through these experiments, we effectively acquired information on the temperature and soot by the two-color method in a turbulent diesel diffusion flame. In addition, this experiment revealed that the KL factor was high on the parts of the chamber where the temperature dropped. On the other hand, the KL factor was low where the temperature increased rapidly. Also, the highest temperatures of the flame in a constant-volume chamber and in a D.I. diesel engine were approximately 2300K and 2400K, respectively. This study suggests the measurement of not only the temperature but also the soot of a diffusion flame of the diesel engine through an optical methodology.     

The effect of exhaust gas recirculation (EGR) on combustion stability, engine performance and exhaust emissions in a gasoline engine

The EGR system has been widely used to reduce nitrogen oxides (NOx) emission, to improve fuel economy and suppress knock by using the characteristics of charge dilution. However, as the EGR rate at a given engine operating condition increases, the combustion instability increases. The combustion instability increases cyclic variations resulting in the deterioration of engine performance and emissions. Therefore, the optimum EGR rate should be carefully determined in order to obtain the better engine performance and emissions. An experimental study has been performed to investigate the effects of EGR on combustion stability, engine performance, NOx and the other exhaust emissions from 1. 5 liter gasoline engine. Operating conditions are selected from the test result of the high speed and high acceleration region of SFTP mode which generates more NOx and needs higher engine speed compared to FTP-75 (Federal Test Procedure) mode. Engine power, fuel consumption and exhaust emissions are measured with various EGR rate. Combustion stability is analyzed by examining the variation of indicated mean effective pressure (COV_imep) and the timings of maximum pressure (P_max) location using pressure sensor. Engine performance is analyzed by investigating engine power and maximum cylinder pressure and brake specific fuel consumption (BSFC).     

A study on the characteristics of combustion variations of compression ignition engine

This paper describes the results of a study of the variation of combustion characteristics in a precombusion chamber type water-cooled diesel engine. Statiscal analysis on cycle-by-cycle variation of combustion characteristics such as rate of pressure rise, heat release rate, and mass burning rate from combustion pressure-crank angle data of one thousand cycles were made under several operating conditions. The influence of engine speed and coolant temperature upon maximum frequency of combustion characteristics are discussed also.     

Temperature transients on engine combustion chamber walls—IV. Application of the finite-difference model to surface thermocouples and wall deposits

The FD computational code developed in Part I (Int. J. Mech. Sci. 33, 775 (1991) [1]) has the capability of handling composite walls having different material layers. This characteristic of the FD model is used to study the effects of thermocouple thickness and material type, as well as substrate material type on surface thermocuple readings. Later, the effects of wall deposits on surface thermocouple readings and engine heat transfer are explained.     

Influence of temperature on cam-tappet lubrication in an internal combustion engine

The transient thermo-elastohydrodynamic (TEHL) lubrication simulation and isothermal elastohydrodynamic (EHL) simulation were performed on the exhausting camtappet friction pair of an internal combustion engine. Although by employing the two models the center pressure, the thickness of the lubricant film and friction coefficient obtained were similar in the changing trend during a rotating cycle, the parameters make a great difference, especially for the thickness of the lubricant film; the TEHL was four times thicker than the EHL. These results show that the temperature should not be neglected in the study of the lubrication of cam-tappet pairs. __________ Translated from Tribology, 2006, 26(4): 362–366 [译自: 摩擦学学报]     

A study on the shaped combustion system using diesel spray impinged on a wall

In modern small compact combustion chambers of diesel engines with high speed injection spray, the wall impaction of spray is encountered. A number of combustion systems have been developed which deliberately employ wall impaction as a means of breaking up the fuel spray and/or directing it in a desired direction. As a link of this, in a further type of geometry, which has been presented by Park et al. cut-off pips were provided for a number of sprays directed not only straight down into combustion chamber centre but also across and down into the bowl in the normal radial direction. The sizes of the pips and their positions were tested for axisymmetrical shape, and their results were analyzed. The further type was simulated in here by using 3D non-orthogonal spray engine code. The simulation results show that the further type is much better than general conventional shapes, i.e. well mixing of fuel vapour and spray high qualified droplet atomization, etc. Thus the improvement of the engine performance is expected by the shaped engine.     

A study on in-cylinder flow field of a 125cc motorcycle engine at low engine speeds

The in-cylinder flow characteristics of a four-stroke, four-valve, pent-roof small engine of motorcycle at engine speeds from 2000 rpm to 4000 rpm were studied using computational fluid dynamics (CFD). The aim of this study was to investigate the in-cylinder flow characteristics of small engines, including tumble, swirl, turbulent kinetic energy (TKE), angular momentum, in-cylinder air mass, turbulent velocity, turbulent length scale, and air flow pattern (in both intake and compression strokes) under motoring conditions. The engine geometry was created using SolidWorks, then was exported and analyzed using CONVERGE, a commercial CFD method. Grid independence analysis was carried out for this small engine and the turbulence model was observed using the renormalized group (RNG) k-ɛ model. The pressure boundary conditions were used to define the fluid pressure at the intake and exhaust of the port. The results showed that the increase in the engine speed caused the swirl flow in the small engine to be irregularly shaped. The swirl flow had a tendency to be stable and almost constant in the beginning of the compression stroke and increased at the end of compression stroke. However, the increase of in engine speed had no significant effect on the increase in tumble ratio, especially during the intake stroke. There was an increase in tumble ratio due to the increase in engine speed at the end of compression stroke, but only a marginal increase. The increase in engine speed had no significant effect on the increase in angular momentum, TKE, or turbulent velocity from the early intake stroke until the middle of the intake stroke. However, the angular momentum increased due to the increase in engine speed from the middle of the intake stroke to the end of compression stroke, and the angular momentum achieved the biggest increase when the engine speed rose from 3000 to 4000 rpm by 10 % at the end of the intake stroke. The increase in engine speed caused an increase of TKE and turbulent velocity from the middle of intake stroke until the end of compression stroke. Moreover, the biggest increase of TKE and turbulent velocity occurred when the engine speed rose from 3000 to 4000 rpm at the middle of intake stroke around 50 % and 25 %, respectively. Turbulent length scales appeared to be insensitive to increasing engine speed, especially in the intake stroke until 490 °CA. From that point, the value of the turbulent length scale increased as engine speed increased. The biggest increase in the turbulent length scales occurred when the intake valve was almost closed (around 20 %) and the engine speed was within two specific ranges (2000 to 3000 rpm and 3000 to 4000 rpm). Regarding the effect of engine speed, there were no significant effects upon the accumulated air mass in the small engine. The increase in engine speed caused an increase of turbulence in the combustion chamber during the late stages of the compression stroke. The increase in turbulence enhanced the mixing of air and fuel and made the mixture more homogeneous. Moreover, the increase in turbulence directly increased the flame propagation speed. Further research is recommended using a new design with several types of intake ports as well as combinations of different intake ports and some type of piston face, so that changes in air flow characteristics in small engines can be analyzed. Finally, this study is expected to help decrease the number of experiments necessary to obtain optimized systems in small engines.

     

A numerical study on the soot and combustion performance of a diesel engine with pip shape

Journal of Mechanical Science and Technology - The shape of the combustion chamber plays an important role in the formation of the air-fuel mixture in the chamber, which has a great influence on...     

Effects of various baffle designs on acoustic characteristics in combustion chamber of liquid rocket engine

Effects of various baffle designs on acoustic characteristics in combustion chamber are numerically investigated by adopting linear acoustic analysis. A hub-blade configuration with five blades is selected as a candidate baffle and five variants of baffles with various specifications are designed depending on baffle height and hub position. As damping parameters, natural-frequency shift and damping factor are considered and the damping capacity of various baffle designs is evaluated. Increase in baffle height results in more damping capacity and the hub position affects appreciably the damping of the first radial resonant mode. Depending on baffle height, two close resonant modes could be overlapped and thereby the damping factor for one resonant mode is increased exceedingly. The present procedure based on acoustic analysis is expected to be a useful tool to predict acoustic field in combustion chamber and to design the passive control devices such as baffle and acoustic resonator.     

Measurement of lubricant flow in a gasoline engine

A residence time of approximately 60 s for lubricant in the piston ring pack of a gasoline engine, running at 1500 rpm, 50% throttle, has been measured by adding a hydrocarbon marker to the oil in the sump and monitoring its build up in oil extracted from the top ring groove. Comparison of the rate of increase of oxidised products in the sump with the level of oxidation in the ring pack allows a rate of flow of oil entering the ring pack from the sump to be calculated as approximately 0.4 cm³ min⁻¹ cylinder⁻¹, with at least 88% returning to the sump and the remainder lost into the combustion chamber. The volume of oil in the ring pack was determined as approximately 0.4 cm³ cylinder⁻¹, approximately one quarter of the free volume available between the top of the oil control ring and the top piston ring.     

Experimental investigation on the effect of charge temperature on ethanol fueled HCCI combustion engine

In this investigation, an attempt has been made to study by varying the charge temperature on the ethanol fueled Homogeneous charge compression ignition (HCCI) combustion engine. Ethanol was injected into the intake manifold by using port fuel injection technique while the intake air was heated for achieving stable HCCI operation. The effect of intake air temperature on the combustion, performance, and emissions of the ethanol HCCI operation was compared with the standard diesel operation and presented. The results indicate that the intake air temperature has a significant impact on in-cylinder pressure, ringing intensity, combustion efficiency, thermal efficiency and emissions. At 170°C, the maximum value of combustion efficiency and brake thermal efficiency of ethanol are found to be 98.2% and 43%, respectively. The NO emission is found to be below 11 ppm while the smoke emission is negligible. However, the UHC and CO emissions are higher for the HCCI operation.

     

大功率柴油机燃烧室优化及其与喷油嘴的匹配试验

运用仿真与试验相结合的方法,利用KIVA-3软件对燃烧室进行了优化研究,确定燃烧室的优选方案。并在一台模拟增压单缸机上对燃烧室的优选方案与不同方案喷油嘴进行优化匹配试验,确定喷油嘴最佳方案。结果表明:采用燃烧室B和8×Ф0.42 mm喷油嘴,可以达到研究目的。     

Supercharging performance of a gasoline engine with a supercharger

Supercharging of intake air can improve the engine power and combustion characteristics by boosting the intake pressure above atmospheric pressure. In this work, the supercharging performance of a supercharged gasoline engine was discussed on the basis of experimental investigation. The investigation results showed that the output and torque performance of a supercharged engine were improved in comparison with the naturally aspirated engine. In the engine system with a supercharger, owing to supercharging of intake air into the cylinder, the combustion pressure, the rate of heat release, and the burning rate of fuel-air mixture were found to be higher than those of the naturally aspirated engine. In this paper, the effect of the drive pulley ratio and the pressure ratio of supercharger, and the other factors on the supercharging performance were also investigated.     

Analysis of compression ignition combustion in a schnurle-type gasoline engine comparison of performance between direct injection and port injection systems-

A two-stroke Schnurle-type gasoline engine was modified to enable compression-ignition in both the port fuel injection and the in-cylinder direct injection. Using the engine, examinations of compression-ignition operation and engine performance tests were carried out. The amount of the residual gas and the in-cylinder mixture conditions were controlled by varying the valve angle rate of the exhaust valve (VAR) and the injection timing for direct injection conditions. It was found that the direct injection system is superior to the port injection system in terms of exhaust gas emissions and thermal efficiency, and that almost the same operational region of compression-ignition at medium speeds and loads was attained. Some interesting combustion characteristics, such as a shorter combustion period in higher engine speed conditions, and factors for the onset of compression-ignition were also examined.     

A study on the mixture formation process of diesel fuel spray in unsteady and evaporative field

The focus of this work is placed on the analysis of the mixture formation mechanism under the evaporative diesel spray of impinging and free conditions. As an experimental parameter, ambient gas density was selected. Effects of density variation of ambient gas on liquid and vapor-phase inside structure of evaporation diesel spray were investigated. Ambient gas density was changed between θ _a= 5.0 kg/m³ and 12.3 kg/m³. In the case of impinging spray, the spray spreading to the radial direction is larger due to the decrease of drag force of ambient gas in the case of the low density than that of the high density. On the other hand, in the case of free spray, in accordance with the increase in the ambient gas density, the liquid-phase length is getting short due to the increase in drag force of ambient gas. In order to examine the homogeneity of mixture consisted of vapor-phase fuel and ambient gas in the spray, image analysis was conducted with statistical thermodynamics based on the non-dimensional entropy (S) method. In the case of application of entropy analysis to diesel spray, the entropy value always increases. The entropy of higher ambient density is higher than that of lower ambient gas density during initial injection period.     

Changes in the mechanical properties of oil used in a gasoline engine

This study is concerned with the changes in and deterioration of the mechanical properties of oil used in a gasoline engine. The properties analysed were friction and antiwear performance, wear debris, load-carrying ability and the formation of surface films. It was found that the oil run in an engine deteriorated so as to increase the wear and friction and decrease the load-carrying ability as the running distance of oil was increased. The main cause of deterioration was related to the ability to form a protective film in the contact zone. When the film was produced by additives (sulphur), this could properly protect the surface in the contact zone undepleted from wear and friction. But as the oil deteriorated, it could not form such a film and so its protective ability on sliding surfaces diminished.     

基于温度场重建的炉膛燃烧数字监测系统

基于温度场重建的炉膛燃烧监测系统利用多路视频采集技术的协调与同步特性就可以实现系统的数字化。通过软硬件相结合,则可以实现多通道火焰图像的同步采集、温度图像计算、三维温度场计算及显示等功能。     

A study on the characteristics of spray and combustion in a HCCI engine according to various injection angles and timings

Premixed diesel engines have the potential to achieve a more homogeneous, leaner mixture near TDC compared to conventional diesel engines. Early studies have shown that the fuel injection timing and injection angle affect the mixture formation in a HCCI (Homogeneous Charge Compression Ignition) engine. Therefore in this study, we investigated the relationship between combustion and mixture formations accordance with injection conditions in a common rail direct injection type HCCI engine using an early injection strategy. From this results, we found that the fuel injection timing and injection angle affect the mixture formation and in turn affect combustion in the HCCI engine. In addition, this study revealed that the injection angle of 100° is effective to reduce smoke emission without any sacrificing power in the early injection case.