共查询到19条相似文献,搜索用时 171 毫秒
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正庚烷化学动力学简化模型的构建及优化 总被引:1,自引:0,他引:1
提出了一个新的适用于HCCI发动机燃烧模拟的正庚烷化学反应动力学简化模型(40种组分和62个反应)。由三个子模型组成:低温反应子模型是在Li等人模型的基础上,定义具体的醛类(RCHO)产物和小分子碳氢产物(Rs)而构建;增加了用于链接低温反应向高温反应过渡的大分子直接裂解成小分子反应子模型;高温反应子模型是在Griffiths等人模型的基础上,去除了无关的基元反应,增加两个关于CO和CH3O的氧化反应而构建。另外,采用遗传优化技术对模型动力学参数进行调整。计算表明,新模型能够在当量比0.2-1.2,温度从300-3000 K的范围内精确模拟正庚烷HCCI燃烧时冷焰和热焰反应过程,与详细模型(544种组分和2446个反应)计算结果吻合较好。 相似文献
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本文构建了一个包含正癸烷、异辛烷、甲苯和甲基环己烷的柴油表征燃料模型。基于解耦法构建了一个包含70种组分和193个反应的柴油表征燃料的骨架机理。在解耦法中,骨架机理被分为两部分:一部分是极其简化的C_2-C_n机理,用于预测燃料的滞燃期和消耗;另一部分为详细的H_2/CO/C_1机理,用于预测火焰速度和熄火极限,以及碳氢和一氧化碳的排放。通过与激波管中的滞燃期、搅拌反应器(JSR)中的组分浓度、层流火焰速度以及预混压燃(PCCI)发动机中的燃烧和排放的实验数据对比,发现机理较好地预测了柴油的着火、燃烧和排放特性。 相似文献
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本文基于Healy等人建立的正丁烷详细反应机理(230个组分,1328个反应),采用直接关系图法,反应路径分析以及敏感性分析相结合的方法,构建了一个包含83个组分,397个反应的中低温反应动力学骨架模型。路径分析发现,在低温反应中,正丁烷氧化着火主要受链传播反应中的放热循环控制。而在中温反应中,正丁烷及其下游产物正丁基的裂解反应变得重要,大分子裂解后的小分子氧化加快反应进程。本文骨架模型在温度范围550~1050 K、压力范围0.1~3MPa、当量比范围0.5~2.0条件下对着火延迟时间、层流火焰速度、温度以及重要组分浓度分布的预测均与详细机理保持很好的一致性,同时与文献中快压机、定容燃烧弹和搅拌射流反应器的实验结果也吻合较好。 相似文献
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《工程热物理学报》2010,(9)
通过敏感性分析、准稳态假设的方法,对含有60个组分、371个基元反应的SNCR详细机理—(?)A机理,进行了系统的简化,得到了包含28个组分、97个基元反应的骨架机理,以及进一步的包含12个主要组分,8步总包反应的简化机理模型。用Chemkin软件中柱塞流反应器(Plug Flow Reactor,PFR)模型对详细机理和简化机理模型分别进行计算,结果表明简化机理相比详细机理计算量大大减小,并在较广的反应温度(800~1300℃)、氨氮摩尔比(0.5~2)、停留时间(0.01~1 s)等范围内可以准确反映详细机理对SNCR化学动力学特性的预测。与普遍使用的Fluent软件中的SNCR两步总包反应模型相比,本文所发展的简化机理模型在适用范围及准确性方面都有显著的改进。本文发展的简化机理模型可以为后续SNCR反应流的数值模拟提供参考。 相似文献
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There is a need to reduce the computational expense of practical multidimensional combustion simulations. Simulation of Homogeneous Charge Compression Ignition (HCCI) engine processes requires consideration of detailed chemistry in order to capture the ignition and combustion characteristics. Even with relatively coarse numerical meshes and reduced chemistry mechanisms, calculation times are still unacceptably long. For the simulation of Direct Injection (DI) engines, fine meshes are needed to achieve the resolution required by the spray and mixing models, and they are computationally expensive even with reduced chemistry. In addition, the increasing application of CFD for engine design optimization is pushing the demand to reduce computational time. In current design optimizations, depending on the size of the parametric space, hundreds of individual simulations are needed. This work presents an efficient Adaptive Multi-grid Chemistry (AMC) model that can be used in engine CFD codes for simulations of HCCI and DI engines with detailed chemistry. It was found that the number of cells computed with the chemistry solver can be reduced by two orders of magnitude for HCCI engines. The results predicted by the present KIVA AMC code are also consistent with those calculated by the original code using every cell. In the method, progressively coarser grids are used for cells with similar gas properties in the chemistry calculation (up to four neighbour levels) or in the global method, cells are grouped without regard for their locations in the cylinder. Averaged and gradient-preserving remapping techniques used in multi-zone engine simulations were also explored. A parametric study was conducted for determining the model variables, such as the degree of local homogeneity for the multi-grid solvers. The simulation results were compared with experimental data obtained from a Honda engine operated with n-heptane under HCCI conditions for which directly measured in-cylinder temperature and H2O mole fraction data are available. In addition, simulation results were found to agree well with experimental data from a DI diesel engine operated under PCCI conditions with ultra-high EGR rates. It was found that computer time was reduced by a factor of ten for HCCI cases and two to three for DI cases without losing prediction accuracy. 相似文献
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《Combustion Theory and Modelling》2013,17(2):417-433
This study used a numerical model to investigate the combustion process in a premixed iso-octane homogeneous charge compression ignition (HCCI) engine. The engine was a supercharged Cummins C engine operated under HCCI conditions. The CHEMKIN code was implemented into an updated KIVA-3V code so that the combustion could be modelled using detailed chemistry in the context of engine CFD simulations. The model was able to accurately simulate the ignition timing and combustion phasing for various engine conditions. The unburned hydrocarbon emissions were also well predicted while the carbon monoxide emissions were under predicted. Model results showed that the majority of unburned hydrocarbon is located in the piston-ring crevice region and the carbon monoxide resides in the vicinity of the cylinder walls. A sensitivity study of the computational grid resolution indicated that the combustion predictions were relatively insensitive to the grid density. However, the piston-ring crevice region needed to be simulated with high resolution to obtain accurate emissions predictions. The model results also indicated that HCCI combustion and emissions are very sensitive to the initial mixture temperature. The computations also show that the carbon monoxide emissions prediction can be significantly improved by modifying a key oxidation reaction rate constant. 相似文献
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Compact reaction schemes capable of predicting auto-ignition are a prerequisite for the development of strategies to control and optimise homogeneous charge compression ignition (HCCI) engines. In particular for full boiling range fuels exhibiting two stage ignition a tremendous demand exists in the engine development community. The present paper therefore meticulously assesses a previous 7-step reaction scheme developed to predict auto-ignition for four hydrocarbon blends and proposes an important extension of the model constant optimisation procedure, allowing for the model to capture not only ignition delays, but also the evolutions of representative intermediates and heat release rates for a variety of full boiling range fuels. Additionally, an extensive validation of the later evolutions by means of various detailed n-heptane reaction mechanisms from literature has been presented; both for perfectly homogeneous, as well as non-premixed/stratified HCCI conditions. Finally, the models potential to simulate the auto-ignition of various full boiling range fuels is demonstrated by means of experimental shock tube data for six strongly differing fuels, containing e.g. up to 46.7% cyclo-alkanes, 20% napthalenes or complex branched aromatics such as methyl- or ethyl-napthalene. The good predictive capability observed for each of the validation cases as well as the successful parameterisation for each of the six fuels, indicate that the model could, in principle, be applied to any hydrocarbon fuel, providing suitable adjustments to the model parameters are carried out. Combined with the optimisation strategy presented, the model therefore constitutes a major step towards the inclusion of real fuel kinetics into full scale HCCI engine simulations. 相似文献
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柴油燃料HCCI燃烧影响因素的试验研究 总被引:4,自引:0,他引:4
本文采用在进气上止点附近进行柴油喷射,利用缸内高温残余废气促进燃油蒸发形成均质混合气,实现了柴油燃料的均质压燃(HCCI)。试验结果表明柴油燃料HCCI燃烧的放热规律呈现低温和高温放热两个阶段,并且NOx排放可以降低95%-98%。本文主要研究了影响HCCI燃烧的因素,指出负荷增大、进气温度增加和负气门重叠期的增加使HCCI着火提前,而外部EGR率的增大可以推迟着火。因此对于低温自燃性好的燃料,冷EGR是控制其HCCI着火燃烧过程的有效措施。 相似文献
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Acceleration of the chemistry solver for modeling DI engine combustion using dynamic adaptive chemistry (DAC) schemes 总被引:1,自引:0,他引:1
Acceleration of the chemistry solver for engine combustion is of much interest due to the fact that in practical engine simulations extensive computational time is spent solving the fuel oxidation and emission formation chemistry. A dynamic adaptive chemistry (DAC) scheme based on a directed relation graph error propagation (DRGEP) method has been applied to study homogeneous charge compression ignition (HCCI) engine combustion with detailed chemistry (over 500 species) previously using an R-value-based breadth-first search (RBFS) algorithm, which significantly reduced computational times (by as much as 30-fold). The present paper extends the use of this on-the-fly kinetic mechanism reduction scheme to model combustion in direct-injection (DI) engines. It was found that the DAC scheme becomes less efficient when applied to DI engine simulations using a kinetic mechanism of relatively small size and the accuracy of the original DAC scheme decreases for conventional non-premixed combustion engine. The present study also focuses on determination of search-initiating species, involvement of the NOx chemistry, selection of a proper error tolerance, as well as treatment of the interaction of chemical heat release and the fuel spray. Both the DAC schemes were integrated into the ERC KIVA-3v2 code, and simulations were conducted to compare the two schemes. In general, the present DAC scheme has better efficiency and similar accuracy compared to the previous DAC scheme. The efficiency depends on the size of the chemical kinetics mechanism used and the engine operating conditions. For cases using a small n-heptane kinetic mechanism of 34 species, 30% of the computational time is saved, and 50% for a larger n-heptane kinetic mechanism of 61 species. The paper also demonstrates that by combining the present DAC scheme with an adaptive multi-grid chemistry (AMC) solver, it is feasible to simulate a direct-injection engine using a detailed n-heptane mechanism with 543 species with practical computer time. 相似文献