共查询到16条相似文献,搜索用时 265 毫秒
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以甲烷/空气的湍流射流非预混燃烧为对象,建立二维稳态湍流非预混火焰的小火焰模型.利用湍流流动模型和小火焰模型耦合求解,计算出速度、混合分数、温度以及反应标量的摩尔分数在燃烧室内的分布,模拟结果表明小火焰模型能够用来描述燃烧室内燃烧机理. 相似文献
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本文将小火焰(flamelet)理论应用于分析柴油/空气湍流扩散燃烧的小火焰结构,以正十二烷同空气的一步反应为基础,建立柴油机燃烧的Flamelet模型,利用数值方法求出了柴油机湍流扩散燃烧的Flamelet结构.并采用假定PDF的方法,选取截尾式高斯分布的概率密度分布函数,将其与Flamelet结构相结合,求得燃烧过程中各参数的时均值,分析得出湍流脉动和非平衡作用对燃烧过程的影响. 相似文献
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为计算直喷式柴油机的主要污染物——碳烟和氮氧化物,提出了RIF计算模型。此小火焰计算模型是通过引入理想混和比分数空间坐标系,将通常坐标系下的组元方程转化到混和比分数空间坐标系下,得出新的组元扩散方程。同时将小火焰计算模型与对流体动力学程序(KIVA-3V)相结合,增加并修改原有计算模块,将湍流喷雾运动和湍流燃烧运动有机分开,计算出直喷式柴油机湍流燃烧后生成的碳烟和氮氧化物,最后通过实验检验了该计算模型。 相似文献
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高速直喷柴油机燃烧室形状与喷孔结构匹配规律的三维仿真研究 总被引:1,自引:0,他引:1
对某高速直喷柴油机的燃烧过程进行了多维仿真计算,研究了燃烧室形状和喷孔结构参数之间的匹配规律.通过变参数研究确定了燃烧室形状和喷孔结构参数之间的匹配规律.为了定量描述燃烧过程中燃油雾化、液体蒸发、油气混合的特性,建立了缸内平均湍流混合速率、燃油蒸气质量分数方差的中间特征参数,同时详细分析了不同当量比油气混合气在燃烧过程中的贡献率.从燃烧的宏观和微观角度综合分析了柴油机燃烧室形状与喷孔结构间的耦合作用机制.结果表明,对于所研究的机型,0.64口径比燃烧室匹配10孔喷油器的方案最优:预混过程好,燃烧速度快,后期扩散燃烧阶段过稀和过浓混合气参与燃烧的比例较小且预混与扩散燃烧放热情况差别小,放热情况更均匀. 相似文献
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《International Journal of Hydrogen Energy》2023,48(4):1602-1624
In the present study, Reynolds-Averaged Navier-Stokes simulations together with a novel flamelet generated manifold (FGM) hybrid combustion model incorporating preferential diffusion effects is utilised for the investigation of a hydrogen-blended diesel-hydrogen dual-fuel engine combustion process with high hydrogen energy share. The FGM hybrid combustion model was developed by coupling laminar flamelet databases obtained from diffusion flamelets and premixed flamelets. The model employed three control variables, namely, mixture fraction, reaction progress variable and enthalpy. The preferential diffusion effects were included in the laminar flamelet calculations and in the diffusion terms in the transport equations of the control variables. The resulting model is then validated against an experimental diesel-hydrogen dual-fuel combustion engine. The results show that the FGM hybrid combustion model incorporating preferential diffusion effects in the flame chemistry and transport equations yields better predictions with good accuracy for the in-cylinder characteristics. The inclusion of preferential diffusion effects in the flame chemistry and transport equations was found to predict well several characteristics of the diesel-hydrogen dual-fuel combustion process: 1) ignition delay, 2) start and end of combustion, 3) faster flame propagation and quicker burning rate of hydrogen, 4) high temperature combustion due to highly reactive nature of hydrogen radicals, 5) peak values of the heat release rate due to high temperature combustion of the partially premixed pilot fuel spray with entrained hydrogen/air and then background hydrogen-air premixed mixture. The comparison between diesel-hydrogen dual-fuel combustion and diesel only combustion shows early start of combustion, longer ignition delay time, higher flame temperature and NOx emissions for dual-fuel combustion compared to diesel only combustion. 相似文献
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Main objective of this study was to demonstrate endoscopic visualization of combustion events in the combustion chamber of a production grade compression ignition (CI) engine. High speed endoscopic imaging was used to provide qualitative information about the in–cylinder combustion for mineral diesel and biodiesel fueled engine operating at different engine loads. These images were analyzed using image processing program developed in MATLAB, in order to determine the ‘start of combustion’ (SoC), ‘spatial soot distribution’ and ‘spatial flame temperature distribution’. In–cylinder pressure and rate of heat release (RoHR) were validated using simulation results obtained by using a KIVA-3V code. The luminosity of flames in the combustion images was relatively lower for biodiesel compared to baseline diesel. Area of soot distribution decreased in later stages of combustion for both test fuels, which indicated superior oxidation of soot particles formed, during the post combustion events. Biodiesel showed relatively lower dissipation of heat, which caused lower soot radiations in the flames. Simulated soot distribution and flame temperature distribution obtained from KIVA-3V code also showed similar behavior and verified the trends observed by combustion chamber endoscopy. 相似文献
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采用KIVA-3V软件耦合多目标遗传优化算法NSGA-3,开展了柴油/天然气双燃料发动机的引燃柴油喷射参数、运行参数和燃烧室结构参数的协同优化研究.将湍流火焰速度封闭模型(TFSC)与PaSR燃烧模型耦合,建立柴油/天然气双燃料发动机复合燃烧模型.结果表明:复合燃烧模型能较好地模拟柴油/天然气发动机的燃烧过程;采用KIVA3V-NSGA3程序进行了双燃料发动机运行参数、喷射参数等多目标参数的协同优化;多目标参数优化结果的数据对比分析揭示了设计参数对目标参数的影响规律;涡流比和喷射参数的变化会对燃烧室内温度、NOx和CH4的分布产生较大影响. 相似文献
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以K IVA-3为计算平台,计算了生物柴油和柴油混合燃料的燃烧过程,并将结果与柴油的燃烧计算结果进行分析比较。结果表明:混合燃料的燃烧效果与纯柴油相似,NO排放没有明显升高,可以作为柴油的替代燃料使用。 相似文献
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Shijin Shuai Neerav Abani Takeshi Yoshikawa Rolf D. Reitz Sung Wook Park 《International Journal of Thermal Sciences》2009,48(9):1786-1799
Current spray models based on the Lagrangian-droplet and Eulerian-fluid (LDEF) method in the KIVA-3V code are strongly mesh dependent due to errors in predicting the droplet–gas relative velocity and errors in describing droplet–droplet collision and coalescence processes. To reduce the mesh dependence, gas-jet theory is introduced to predict the droplet–gas relative velocity, and a radius of influence (ROI) of collision methodology is established for each gas phase cell to estimate the collision probability for each parcel in the cell. Spray and combustion processes in a low temperature combustion diesel engine under early and late injection strategies with a fine mesh were predicted using the conventional LDEF model and compared with the measurements of soot, OH, fuel liquid and vapor distributions obtained by laser based diagnostics including, PLIF, LII, and Mie scattering. Then, the KIVA-3V code implemented with the improved spray model based on the gas-jet model and modifications of the spray models was utilized to simulate the processes on a relatively coarse numerical mesh. Comparison of the simulations between the fine and coarse meshes shows that the improved spray model can greatly reduce the mesh dependence for low temperature combustion diesel engine CFD simulations. 相似文献