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1.
详细化学反应机理的引入会给燃烧数值模拟带来巨大的困难:一方面,由于不同组分对应不同的特征时间,详细化学反应机理会导致燃烧模拟涉及到广泛的时间尺度;另一方面,随着燃料所含碳原子数目的增加,其详细化学反应机理中所含的组分数目与基元化学反应数目会呈指数增长,这直接导致计算量的急剧增加。为了解决这两方面的困难,本文以正庚烷氧化机理为例,通过化学反应机理简化(反应路径分析法)与加速算法(投影法)实现了在确保计算精度的条件下极大程度地提高计算效率。  相似文献   

2.
在高十六烷值燃料中加入高辛烷值燃料是控制均质混合气压缩着火(HCCI)燃烧的一种有效策略。本文利用快速压缩机模拟发动机HCCI燃烧过程,在正庚烷中分别添加异辛烷和乙醇,发现在部分稀燃条件下出现低温放热和高温两阶段放热的三阶段放热现象。进一步采用详细化学动力学模拟计算,结果表明乙醇对正庚烷燃烧起到抑制作用。高温第一阶段放热主要由CH_2O生成大量CO放热引起,高温第二阶段放热主要由生成燃烧最终产物CO_2和H_2O的反应引起。  相似文献   

3.
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   

4.
本文构建了一个适用于HCCI燃烧的PRF化学反应动力学骨架机理。该机理包含40种组分和65个反应。通过与激波管、喷射搅拌反应器、流动反应器和HCCI发动机的实验数据对比表明,新机理适用于多种反应器,可以较准确地计算着火点及关键组分的演变规律,并且在不同的温度、压力和当量比下具有较好的性能。在HCCI发动机的单区模型计算中,对于燃料PRF 91.8和PRF 70,骨架机理计算结果与Curran等人的详细机理计算结果基本相同。  相似文献   

5.
废气再循环和添加剂对高辛烷值燃料HCCI燃烧的影响   总被引:1,自引:0,他引:1  
本文对废气再循环(EGR)和十六烷值改进荆-过氧化二叔丁基(DTBP)对高辛烷值燃料HCCI燃烧的影响进行了研究。实验结果表明:辛烷值为90的燃料(RON90)只能在高温高负荷下才能运行HCCI燃烧模式;在其中加入少量的DTBP后,RON90实现HCCI燃烧的工况范围向低温低负荷下大幅度拓展。加入添加剂后,低负荷性能改善的同时,浓混合气的着火时刻可以通过EGR将含添加剂燃料的着火时刻推迟到上止点附近,从而大幅度提高热效率,降低了燃料消耗率。  相似文献   

6.
基于详细化学反应机理的燃烧数值模拟是当今燃烧领域的重要研究方向.由于燃烧问题涉及众多的化学反应和广泛的特征时间范围,如何实现燃烧问题的高效精确数值模拟一直是目前研究难点.本文将HDMR方法应用于模拟零维均质着火过程中,通过与完全求解刚性微分方程组的结果相比较,验证了HDMR方法在处理详细化学反应机理方面的计算精度与效率...  相似文献   

7.
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   

8.
湍流扩散火焰局部熄火和再燃现象的PDF模拟   总被引:2,自引:0,他引:2  
王海峰  陈义良 《计算物理》2004,21(6):471-476
对一个值班湍流CH4/O2/N2射流扩散火焰(Sandia Flame D)进行了数值模拟研究.所采用的数学物理模型包括双尺度的k—ε湍流模型,标量联合的概率密度函数(PDF)输运方程方法,甲烷氧化的ARM简化化学反应机理(包含16种组分,12步总包反应)和欧几里德最小生成树(EMST)小尺度混合模型.将计算结果和实验数据进行了比较,不仅对于平均量,对于标量的散点分布和条件概率密度分布也是如此.计算结果表明文中采用的模型不仅能够预测宏观的火焰结构,而且预测了湍流燃烧中复杂的局部熄火和再燃过程.  相似文献   

9.
采用基于详细化学反应机理的三维湍流燃烧数值模拟,研究直喷柴油机燃用二甲基醚(DME)的伴有化学反应的流动燃烧现象.模拟预测的缸内压力随曲轴转角的变化及NO排放浓度与实验相符.分析了计算所得的曲轴转角随缸内流场速度、温度和组分浓度的分布历程,结果表明甲醛在低中温下相对稳定,随着温度的升高,氧化反应加速进行,而由于流动及壁面传热等效应,甲醛作为不完全燃烧产物存在于排气中.  相似文献   

10.
王晶  张漫 《工程热物理学报》2021,42(12):3286-3295
采用不同的航空煤油化学反应机理和碳烟成核模型对气态航空煤油扩散火焰中碳烟颗粒的质量浓度和数量浓度进行预测.分别采用航空煤油详细化学反应机理和简化化学反应机理,结合非预混稳态扩散火焰面模型模拟燃烧反应.分别采用C2H2成核模型(基于乙炔浓度)和PAH成核模型(基于多环芳香烃浓度)预测碳烟颗粒浓度分布.研究结果表明,采用详细化学反应机理和PAH成核模型对碳烟体积分数的预测值与试验值吻合很好.相比于C2H2成核模型,采用PAH成核模型对碳烟体积分数的预测精度显著提升.  相似文献   

11.
二甲醚HCCI燃烧高温反应动力学分析   总被引:1,自引:0,他引:1  
应用单区燃烧模型对二甲醚均质压燃燃烧的化学反应动力学过程进行了数值模拟研究。通过分析在内燃机压燃燃烧边界条件下二甲醚高温氧化反应过程中的关键基元反应速度、关键中间产物以及自由基的浓度随曲轴转角的变化,得到了二甲醚燃烧氧化的高温反应途经。结果表明,二甲醚均质压燃燃烧具有明显的两阶段放热特性,即低温反应放热和高温反应放热。高温反应阶段又可分为蓝焰反应阶段和热焰反应阶段,其中蓝焰反应阶段是甲醛氧化成CO的过程,热焰反应主要是CO氧化成CO2的过程。二甲醚氧化产物之一甲酸(HOCHO)在蓝焰反应阶段分解生成CO2。  相似文献   

12.
Fuel-rich combustion of methane in a homogeneous-charge compression-ignition (HCCI) engine can be used as a polygeneration process producing work, heat, and useful chemicals like syngas. Due to the inertness of methane, additives such as dimethyl ether (DME) are needed to achieve ignition at moderate inlet temperatures and to control combustion phasing. Because significant concentrations of DME are then needed, a considerable part of the fuel energy comes from DME. An alternative ignition promotor known from fuel-lean HCCI is ozone (O3). Here, a combined experimental and modelling study on the ignition of fuel-rich partial oxidation of methane/air mixtures at Φ = 1.9 with ozone and DME as additives in an HCCI engine is conducted. Experimental results show that ozone is a suitable additive for fuel-rich HCCI, with only 75 ppm ozone reducing the fuel-fraction of DME needed from 11.0% to 5.3%. Since ozone does not survive until the end of the compression stroke, the reaction paths are analyzed in a single-zone model. The simulation shows that different ignition precursors or buffer molecules are formed, depending on the additives. If only DME is added, hydrogen peroxide (H2O2) and formaldehyde (CH2O) are the most important intermediates, leading to OH formation and ignition around top dead center (TDC). With ozone addition, methyl hydroperoxide (CH3OOH) becomes very important earlier in the compression stroke under these fuel-rich conditions. It is then later converted to CH2O and H2O2. Thus, ozone is a very effective additive not only for fuel-lean, but also for fuel-rich combustion. However, the mechanism differs between both regimes. Because less of the expensive additives are needed, ozone could help improving the economics of a polygeneration process with fuel-rich operated HCCI engines.  相似文献   

13.
The autoignition of dimethyl ether (DME) with temperature inhomogeneities is investigated by one-dimensional numerical simulations with detailed chemistry at high pressure and a constant volume. The primary purpose of the study is to provide an understanding of the autoignition of DME in a simplified configuration that is relevant to homogeneous charge compression ignition (HCCI) engines. The ignition structure and the negative temperature coefficient (NTC) behaviour are characterised in a homogeneous domain and one-dimensional domains with thermal stratification, at different initial mean temperatures and length scales. The thermal stratification is shown to strongly affect the spatial structure and temporal progress of ignition. The importance of diffusion and conduction on the ignition progress is assessed. It is shown that the effects of molecular diffusion decay relative to those of chemical reaction as the length-scale increases. This is to be expected, however the present study shows that these characteristics also depend on the mean temperature due to NTC behaviour. For the range of conditions studied here, which encompass a range of stratification length scales expected in HCCI engines, the effects of molecular transport are found to be small compared with chemical reaction effects for mean temperatures within the NTC regime. This is in contrast to previous work with fuels with single-stage ignition behaviour where practically realisable temperature gradients can lead to molecular transport effects becoming important. In addition, thermal stratification is demonstrated to result in significant reductions of the pressure-rise rate (PRR), even for the present fuel with two-stage ignition and NTC behaviour. The reduction of PRR is however strongly dependent on the mean initial temperature. The stratification length-scale is also shown to have an important influence on the pressure oscillations, with large-amplitude oscillations possible for larger length scales typical of integral scales in HCCI engines.  相似文献   

14.
The prospects of 2,5-dimethylfuran (DMF) as a bio-derived fuel that can be blended with gasoline are believed to be impressive. However, the effects of blending DMF on the key combustion parameters like the laminar burning velocity and ignition delay time of gasoline/air mixture need to be studied extensively for the successful implementation of the fuel mixture in spark ignition engines. Therefore, a skeletal chemical kinetic mechanism, comprising of 999 reactions among 218 species, has been developed in the present work for this purpose. The proposed chemical kinetic model has been validated against a wide range of experimental data for the laminar burning velocity and ignition delay time of isooctane (representing gasoline), DMF and their blends. It has been found from the present study that the thermal diffusivity of the unburnt gas mixture changes by a very small amount from the corresponding value for the pure isooctane/air mixture when DMF is added. Unlike isooctane, the DMF molecule does not consume H radicals during its primary breakup. Therefore, the maximum laminar burning velocity increases marginally when 50% DMF is blended with isooctane due to the increased presence of H radicals in the flame. The negative temperature coefficient behaviour in the ignition delay time of the isooctane fuel vanishes when 30% DMF (v/v) is blended to it.  相似文献   

15.
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   

16.
燃油分级多点喷射低污染燃烧室的化学反应网络模型分析   总被引:4,自引:0,他引:4  
本文采用基于详细化学反应机理的化学反应网络模型分析了航空发动机燃油径向分级多点喷射低污染燃烧室的NO_x排放特性。该分级燃烧室不同于传统燃烧室,头部由值班区和主燃区两个不同的燃烧区域,根据CFD得到的流场特性和当量比的分布特性对燃烧室进行分区构建化学反应器网络模型,研究了值班级当量比以及值班级和主燃级两级供油比例对排放的影响。同时,还分析了空气进口温度对NO_x排放的影响。得到了较为合理的变化趋势,为低污染燃烧室的初步设计提供了有益的指导。  相似文献   

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