氢气/柴油发动机燃油雾化特性的研究

在柴油引燃氢气/柴油发动机中,通过柴油引燃氢气/空气的预混合气,故有希望实现准均质和低温燃烧.氢气/空气混合气氛围中的柴油雾化特性将直接影响到柴油在气缸内的分布,影响内燃机的燃烧过程,从而决定发动机准均质燃烧的程度,是发动机能否实现低温燃烧的关键.利用KIVA-3V程序对柴油在氢气/空气混合气氛围中的雾化特性进行研究,研究结果表明,氢气的存在能够在一定程度上促进柴油液滴的雾化,增大柴油喷射终了时的缸内柴油蒸气质量;氢气的存在对喷雾油束的偏转和喷雾的贯穿距离具有明显的影响,能够在一定程度上降低液滴碰壁强度,从而有助于气缸内形成较均匀的柴油蒸气分布;但氢气浓度超过一定值后则会增大柴油液滴碰壁的概率.     

不同甲醇预混合气引燃燃烧模式燃烧特性分析

针对甲醇、生物柴油和聚甲氧基二甲醚PODE的优势,为了改善经济性,在一台CY25柴油机上分析不同引燃燃料对甲醇预混合气引燃燃烧模式燃烧特性的影响。试验结果表明:PODE引燃模式的排放特性较差,CO浓度相较生物柴油模式可高达2-3倍。在大甲醇质量比下HC排放浓度可高达生物柴油的5倍。甲醇质量比较小时促进了NO_(X)生成,增大质量比可以降低NO_(X)浓度。生物柴油引燃模式的排放特性随甲醇质量比变化较平稳,PODE引燃模式则随甲醇质量比变化增长较快。     

石油液化气空气混合气燃烧装置安全控制系统

介绍了冶炼铜生产过程中石油液化气－空气混合气燃烧装置的工艺流程和安全控制系统的设计。安全控制系统通过对压力、火焰状态、气体泄漏进行检测、报警、联锁控制，使得燃烧装置的安全性，可靠性得以解决。     

醇醚燃料组合燃烧模式下发动机燃烧特性研究

对一台CY25柴油机进行改造,加装进气道喷嘴。利用均质混合气引燃组合燃烧模式的优势,用高十六烷值的聚甲氧基二甲醚引燃甲醇空气预混合气。研究压缩比对不同甲醇占能比下燃烧始点、燃烧持续期、放热率、压力升高率、缸内压力及相位的影响。研究表明,甲醇高汽化潜热值导致燃烧初期缸内温度降低,燃烧相位后移,不同压缩比下各燃烧特性随甲醇占能比提高,变化趋势相同,波动幅度存在差异,随着压缩比升高放热率峰值、压力升高率峰值、缸内压力峰值、缸内温度峰值最大增幅达34.9%、41.8%、30%、25%,同时对发动机经济性进行了分析。     

点火位置对射流点火发动机燃烧特性的影响

射流点火可以有效提高发动机燃烧效率,抑制爆震,预燃室内部火花塞的点火位置对于点火成功率以及燃烧效果有较大影响。采用CFD仿真的方法,研究了被动式射流点火发动机预燃室内部火花塞点火位置对发动机缸内燃烧过程的影响,得到以下结论：适当的将预燃室内火花塞点火位置靠近预燃室喷孔可借助高湍动能气体实现火焰的加速传播;在气流作用下,火焰首先向预燃室末端传播,可减少高温燃气喷射前预燃室向主燃室回流的未燃混合气,提高预燃室内混合气的累计放热量,预燃室内可燃混合气累计放热率最高可提升14.9%。     

农机使用中的节油技术

(1)按期定时保养空气滤清器.尤其是遇田间尘土多、作业环境恶劣时,机车保养周期应缩短,使其始终保持清洁与畅通.否则容易造成滤清器被堵,空气供应不足,混合气变浓,致使柴油不能充分燃烧,增加了不必要的油耗.①空气滤清器的保养周期一般是工作100h,但实际工作中要视空气中含尘情况而定,作业环境条件差,保养周期相应缩短.     

甲烷二次燃烧火焰传播速度的数值模拟研究

二次燃烧是常见热力设备和高速推进燃烧室内的重要现象,但目前对二次燃烧的研究较为匮乏。为了研究当量比、甲烷添加量对二次燃烧自点火火焰传播速度的影响情况,论文利用CHEMKIN软件中火焰速度反应器模拟研究了向不同当量比(0.3~0.9)甲烷/空气一次燃烧产物中添加不同量(摩尔分数0.02~0.24)甲烷时的自点火火焰传播速度。研究表明当量比主要是通过影响尾气温度和一次燃烧产物中富余氧气来影响火焰传播速度,而甲烷添加量会影响二次燃烧时局部当量比,局部当量比在1附近时火焰传播速度最大。     

滑动弧等离子体强化甲烷/空气扩散火焰燃烧研究

为评估滑动弧等离子体对甲烷/空气正扩散火焰的点火助燃效果,采用定常和非定常两种放电模式,保持甲烷流量不变,对不同空气流量、占空比下的甲烷/空气正扩散火焰进行实验测量。实验结果表明:滑动弧等离子体可以增大甲烷/空气正扩散火焰的点火极限,能够点燃熄灭火焰,并使火焰稳定燃烧;在两种放电模式下,将空气流量从5L/min增加到9L/min,火焰高度降低,CH基的生成增加;在非定常模式下,将交流电源放电占空比从10%增加到90%,火焰高度和CH基生成均会增加。     

工程机械的低温启动

柴油机能否顺利启动,关键在于喷入气缸的柴油能否与被压缩的空气迅速形成可燃混合气并及时着火燃烧,因此,要求进入气缸的空气被压缩后有较高的温度和压力。启动的基本条件：要有足够的启动转速,启动转速高气体渗漏少,压缩空气向气缸壁传热的时间短、热量损失少,可以提高压缩终了时空气的温度和压力;气缸密封性要好,启动时气体渗漏少,     

柴油甲醇双燃料发动机动力性与经济性试验分析

介绍了柴油引燃甲醇双燃料燃烧对柴油机动力性和经济性的影响。在1台单缸、直喷、中冷柴油机上采用柴油引燃甲醇双燃料进行试验。结果显示甲醇柴油双燃料发动机在中高负荷及中高转速下运转可获得较好的燃油经济性。选择适当的引燃柴油量,双燃料发动机的动力性可以达到甚至超过原柴油的动力性。     

Prediction of flame formation in highly preheated air combustion

Fundamental information about the ignition position and shape of a flame in highly preheated air combustion was obtained, and the suitability of the suggested reduced kinetic mechanism that reflects the characteristics of the highly preheated air combustion was demonstrated. Flame lift height and flame length with variations of premixed air temperature and oxygen concentration were measured by CH* chemiluminescence intensity, and were computed with a reduced kinetic mechanism. Flame attached near a fuel nozzle started to lift when preheated air temperature became close to auto-ignition temperature and/or oxygen concentration reduced. The flame lift height increased but the flame length decreased with decreasing preheated air temperature and flame length reversed after a minimum value. Calculated results showed good agreement with those of experiment within tolerable error. Flame shape shifted from diffusion flame shape to partial premixed flame shape with increasing lift height and this tendency was also observed in the computation results. This paper was recommended for publication in revised form by Associate Editor Ohchae Kwon Gyung-Min Choi studied the areas of combustion engineering, heat recirculating combustion, and solid fuel gasification, receiving his Ph.D. degree in engineering from Osaka University in 2001. He served as a researcher at Japan Aerospace Exploration Agency and is now an associate professor in the School of Mechanical Engineering at Pusan National University.     

An experimental investigation of the engine operating limit and combustion characteristics of the RI-CNG engine

In this paper, the radical induced (RI) ignition method was applied into a compressed natural gas (CNG) engine to achieve rapid bulk combustion. The experimental RI-CNG engine was modified from a diesel engine. The combustion chamber of the modified diesel engine was divided into a sub-chamber and a main-chamber. The sub-chamber is physically separated from the main-chamber above the piston and is connected to the main-chamber via several passage holes. CNG is injected into the sub-chamber during the intake stroke and then ignited before the top dead center (TDC) by a spark plug. As the ignition occurs in the sub-chamber, the pressure rises, forcing the gases which contain a number of active radicals out into the main-chamber to ignite the unburned mixture. The purpose of this paper is to study the engine operating limit and the combustion characteristics of the RI-CNG engine. The engine operating limit was accessed with different engine speeds and injection timings. The obtained data including the coefficient of variation (COV), brake specific fuel consumption (BSFC), mass fraction burned and emissions were analyzed.     

Effect of oxygen enrichment on the performance,combustion, and emission of single cylinder stationary CI engine fueled with cardanol diesel blends

We investigated the effect of intake air enrichment on the performance, combustion, and emission characteristics of a single cylinder direct-injection stationary diesel engine fueled with non- edible alternative fuel, namely, cardanol — diesel — methanol blend (B20M10). The results were compared with baseline diesel operations under standard operating conditions. The bio-fuel blend B20M10 (20% cardanol, 10% Methanol, and 70% diesel) was used as fuel and the combustion, performance, and emission characteristics were investigated by oxygen enriching of intake air with 3, 5, and 7 percentage by weight. With the increase of intake air oxygen concentration, CO, HC, and smoke were found to be decreased. But BTE and NOx emission were considerably increased. The blended fuel B20M10 with 7% oxygen enrichment of intake air was compared with diesel operation. The results show a 0.5% lesser BTE, 28% more NOx emission at full load condition. There is not much variation of smoke emission to be noticed for this fuel combination compared to diesel.     

An investigation of the spray characteristics of diesel-DME blended fuel with variation of ambient pressure in a constant volume combustion chamber

We compared the spray characteristics of a typical fuel (100% diesel, DME) and diesel-DME blended fuel in a constant volume combustion chamber (CVCC). The typical fuel (100% diesel, DME) and diesel-DME blended fuel spray characteristics were investigated at various ambient pressures (pressurized nitrogen) and fuel injection pressures using a common rail fuel injection system when the fuel mixture ratio was varied. The fuel injection quantity and spray characteristics were measured including spray shape, penetration length, and spray angle.     

Feasibility and performance study of turpentine fueled DI diesel engine operated under HCCI combustion mode

In the present investigation a volatile fraction of Pinus resin called Turpentine has been experimented in a direct injection diesel engine under HCCI combustion mode. The engine chosen to experiment is a single cylinder DI diesel engine and modified in such a way to ignite Turpentine in a diesel engine under HCCI mode. As the Turpentine has a higher self ignition temperature the ignition of Turpentine in regular diesel engines with auto-ignition is not possible. Hence, suitable modification is made in the engine to ignite Turpentine in a diesel engine like diesel fuel. The modified engine has ECM controlled fuel spray and an air preheater in the suction side of the engine. The combined effort of adiabatic compression and supply of preheated air ignites turpentine by auto-ignition and its timing of ignition is precisely controlled by changing intake air temperature. This investigation revealed that the engine operated with turpentine performed well with little loss of brake thermal efficiency. And, emitted comparatively lower emissions such as NO_x and smoke and proved that the turpentine is a best suited fuel for HCCI operation.     

Comparisons of predicted and measured results on performance and emission of engine effected by intake air dilution and supercharging

An experimental study was conducted on a single cylinder direct injection diesel engine to investigate the effects of diluting intake air, with different gases and increasing intake pressure on combustion process and exhaust emissions. The intake O₂ concentration is changed from 15% to 21% by diluting intake air with different gases (CO₂, Ar, N₂), and the intake pressure is changed from one to two bar by a screw compressor. A modified program for calculating heat release rate, is used to study the characteristics of combustion and exhaust emissions in detail. The main results show that the addition of either CO₂ or Ar to the intake air increases the ignition delay. The variations of ignition delay with CO₂ are much larger than those of ignition delay with Ar for the same O₂ concentration. The emission of NOx decreases with the decrease of O₂ concentration and the smoke level is lower with the addition of the CO₂ than with that of Ar. As the intake pressure is increased, the ignition delay is shortened. Furthermore the high intake air pressure enhances the air-fuel mixing and diffusion combustion, and reduces the premixed combustion, so that NOx emission is decreased without increasing smoke emissions. The addition of CO₂ at high intake pressure, drastically reduces NOx emissions and smoke emission simultaneously at a high load condition, and the addition of CO₂ reduces NOx emissions without affecting the smoke emissions substantially at a low load condition. A zero-dimensional combustion simulation program incorporated with the present heat release correlation and ignition delay correlation is used to predict ignition delay, cylinder pressure and engine power. The results show that the correlations are likely to be adequate for the engine operating under diluted intake air and various intake pressure.     

EFFECTS OF COOLED EXTERNAL EXHAUST GAS RECIRCULATION ON DIESEL HOMOGENEOUS CHARGE COMPRESSION IGNITION ENGINE

The effects of cooled external exhaust gas recirculation (EGR) on the combustion and emission performance of diesel fuel homogeneous charge compression ignition (HCCI) are studied. Homogeneous mixture is formed by injecting fuel in-cylinder in the negative valve overlap (NVO) period. So, the HCCI combustion which has low NOx and smoke emission is achieved. Cooled external EGR can delay the start of combustion effectively, which is very useful for high cetane fuel (diesel) HCCI, because these fuels can easily self-ignition, which makes the start of combustion more early. External EGR can avoid the knock combustion of HCCI at high load which means that the EGR can expand the high load limit. HCCI maintains low smoke emission at various EGR rate and various load compared with conventional diesel engine because there is no fuel-rich area in cylinder..     

Effects of turbulent mixing on spray ignition in spray system

When a column of droplets freely falling from an ultrasonic atomizer was ignited behind a reflected shock, no ignition occurred at a temperature below 1100 K, even if the pressure was as high as IMPa. Although, a higher temperature condition ensured ignition, no luminous flame was observable by high-speed photography, and even if a luminous flame lump appeared at an extremely high temperature, it disappeared without spreading over the entire column of droplets in this case. It is known however that, if a fuel is injected into a diesel cylinder or an electric furnace, ignition occurs even at a temperature as low as 650 K with a luminous flame spreading over the entire spray. These differences could be caused by the effects of turbulent mixing between fuel droplets and hot air, in fact, turbulence-generating rods were placed on the upstream side of the spray column. Experimental results indicates that the ignition limit was lowered to 840 K, and the ignition delay period was decreased by increasing the intensity of turbulence. Furthermore, the light emission of the flame was intensified, and normal spray combustion was maintained in the low-temperature atmosphere after the shock tube ceased its operation.     

柴油机燃烧室匹配参数对撞壁喷雾特性的影响

利用高速纹影摄像技术,研究了喷油器喷孔角度、喷孔与活塞顶面间的撞壁距离、燃烧室缩口半径和凸台夹角对柴油撞击燃烧室壁面后喷雾特性的影响。研究结果表明,试验条件下适宜的喷孔角度为75°,增大喷孔角度可以促进喷雾撞壁后的油气混合,但是喷孔角度过大会增加油束撞击气缸盖和气缸套的风险;适宜的撞壁距离为4.2mm,即压缩上止点前15°CA（CA指曲轴转角）,较小的撞壁距离会促进喷雾液滴在凹坑区域的碰撞与黏结,而较大的撞壁距离不利于燃烧室中心区域的空气利用;此外,适当增大缩口半径可以促进燃油与空气的混合,减小燃烧室壁面的燃油湿壁面积;改变凸台夹角可以控制撞壁后喷雾在燃烧室中心区域的扩散速度。     

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...