高温空气燃烧的模型比较数值研究

为验证适用于高温空气燃烧过程的燃烧模型,应用EBU模型、E-A模型、PDF模型三种燃烧模型模拟了一个2m×2m×6.25m的高温空气燃烧室的燃烧过程,并根据国际火焰协会的实验数据对模拟结果进行了验证与比较。湍流输运模型和辐射传热模型分别采用了Reynolds应力模型(RSM)湍流模型和离散坐标(DO)辐射传热模型。结果表明,在预测燃烧室温度、燃料组分体积分数和出口NO体积分数上,EBU模型预测值比E-A模型和PDF模型更符合实验测量值。EBU模型是三种模型中最适合模拟高温空气燃烧的燃烧模型。     

柴油机缸内火焰辐射传热新模型

柴油机缸机的火焰辐射受诸多因素的影响,用理论分析法来确定它是相当困难的,由于柴油机缸内火焰辐射特性依赖于缸内的燃烧过程,而燃烧过程中的实际热力状态又可用示功图来分析,因此借助于火焰辐射与缸内热力参数之间的这种间接关系,建立了一种计算柴油机缸内火焰辐射传热的新模型,利用该模型对一台直喷柴油机缸内火焰辐射热流量随曲轴转角的变化情况进行了计算,将计算结果与实测结果进行了比较,表明该模型能较好预测缸内火焰     

甲烷预混多喷嘴阵列燃烧器热声振荡模态实验研究

为研究燃气轮机模型燃烧室的非预混燃烧流场,采用大涡模拟方法分别结合火焰面生成流形模型（FGM）和部分预混稳态火焰面模型（PSFM）对甲烷/空气同轴射流非预混燃烧室开展了数值模拟研究,并与试验结果进行对比。结果表明：FGM所预测的速度分布、混合分数分布、燃烧产物及CO分布与试验结果更符合;两种模型均能捕捉到燃烧室中的火焰抬举现象;燃烧过程中的火焰结构较为复杂,同时存在预混燃烧区域和扩散燃烧区域,扩散燃烧主要分布在化学恰当比等值线附近,预混燃烧区域主要分布在贫油区。     

用三区模型预测柴油机缸内流动

本文建立了进气模型和压缩过程三区模型,以研究直喷式柴油机缸内涡流和挤流强度的分布规律。研究结果将用作喷雾分布和燃烧过程计算的重要参数。利用稳流试验数据,首先计算进气过程的瞬时进气涡流和缸内瞬时平均涡流等参数,进而揭示压缩过程中缸内不同区域的涡流衰减和挤流强度,并可预测这些参数随燃烧室主要结构参数和运转工况变化的规律。模型物理概念清晰,计算简便,计算结果得到了试验和其它文献的证实。     

汽油机燃烧过程中气缸内对流换热的数值模拟

本文对Morel的汽油机缸内对流换热模型进行了改进,把一维模型应用于燃烧过程的计算,可以体现汽油机燃烧时缸内温度、组分浓度和湍流的空间变化对对流换热的影响,得到燃烧时对流换热量随时间的变化和在缸内的径向分布情况.计算实例表明,面积平均的对流换热系数远大于Woschni公式得到的计算值,缸内热流量的变化与火焰面的位置有密切关系.应用本文的数值模拟方法,还可以预测发动机的几个参数改变时,对流换热量的相应变化情况.     

双燃料直喷发动机喷孔几何位置对燃烧排放的影响

基于柴油引燃天然气缸内直喷发动机,采用AVL-Fire软件研究了天然气和柴油喷孔相对交角、相对距离和相对夹角这3个重要几何参数对燃烧排放的影响.结果表明:两喷孔相对交角影响NOx和碳烟(soot)排放,NO最小生成量比最大生成量少36%,,通过改变相对交角可以同时降低NO和soot排放,但对缸内平均压力的影响较小;两喷孔相对距离会影响污染物生成,并且相对距离越小,温度场分布越均匀,发动机缸内平均压力越高;两喷孔相对夹角减小时,发动机缸内平均压力升高,NO_x排放增加.研究结果对双燃料直喷发动机的两喷孔相对位置的优化有一定的指导作用.     

PaSR湍流燃烧模型对典型湍流射流火焰的数值模拟

采用PaSR湍流燃烧模型对湍流燃烧研究中典型的甲烷湍流射流火焰进行了数值模拟.计算采用简化的化学反应机理,并将计算得到的平均温度场、速度场和各组分的分布与相应的权威实验数据进行了对比.对反应系统中流动和燃烧的不同时间尺度以及二者之间的关系作了探讨.计算结果表明,PaSR模型能够很好地模拟燃烧过程中流场和组分的变化.在火...     

双燃料发动机的燃烧模型

针对双燃料发动机燃烧特性，建立了柴油喷雾扩散燃烧子模型和气体燃烧均质混合气火焰传播燃烧子模型，应用该模型研究了双燃料发动机燃烧机理，计算结果和实验结果相当吻合。计算表明：当引燃柴油比例较大时，双燃料发动机燃烧过程以喷雾混合控制燃烧为主，柴油喷雾扩散燃烧模型与实测较吻合；当柴油比例较小时，该过程以均质混合气火焰传播燃烧为主，均质混合气火焰传播燃烧模型与实测软吻合。计算结果表明，引燃柴油量对双燃料发动机性能影响较大，引燃柴油减少，着火滞燃期延长，缸内最大爆发压力升高。     

新型燃烧模型在柴油机燃烧模拟中的应用(上)

将每个计算单元分为燃料区、空气区和混合区3个区域,在火焰传播方向上又将每个区域分为已燃区和未燃区,建立了柴油机的三区相关火焰燃烧模型,利用该模型对超多喷孔柴油机和传统柴油机缸内燃烧过程进行三维数值模拟,不仅得到了与试验值相符的气缸压力、NOx和SOOT排放量等结果,而且获得了柴油机缸内混合气的浓度场、温度场、NOx质量...     

新型燃烧模型在柴油机燃烧模拟中的应用(下)

将每个计算单元分为燃料区、空气区和混合区3个区域,在火焰传播方向上又将每个区域分为已燃区和未燃区,建立了柴油机的三区相关火焰燃烧模型,利用该模型对超多喷孔柴油机和传统柴油机缸内燃烧过程进行三维数值模拟,不仅得到了与试验值相符的气缸压力、NOx和SOOT排放量等结果,而且获得了柴油机缸内混合气的浓度场、温度场、NOx质量...     

Research on emission characteristics of hydrogen fuel internal combustion engine based on more detailed mechanism

A CFD simulation model with simplified chemical reaction mechanism was built based on CONVERGE software to study the in-cylinder combustion progress and NO generation mechanism of hydrogen fueled internal combustion engine (HICE). Simulation results show that the in-cylinder combustion progress experiences the ellipsoidal flame stable propagation stage and the rapid turbulent combustion stage. At the end of rapid turbulent combustion the OH concentration decreases quickly, the peak temperature and maximum NO mass appear at that time, and then the in-cylinder temperature and NO mass decrease step by step. The final emission depends on the peak temperature and NO decomposition time of high-temperature regions. The higher the maximum temperature, the greater the NO peak mass; and the faster the temperature drop, the less the NO decomposes. Adoption of EGR can reduce the in-cylinder maximum temperature, and NO decomposes sufficiently at low speed, which in turn leads to lower NO emission of HICE.     

Modeling study of soot formation and oxidation in DI diesel engine using an improved soot model

Particulate emission is one of the most deleterious pollutants generated by Diesel fuel combustion. The ability to predict soot formation is one of the key elements needed to optimize the engine performance and minimize soot emissions. This paper reports work on developing, a phenomenological soot model to better model the physical and chemical processes of soot formation in Diesel fuel combustion. This hybrid model features that the effect of turbulence on the chemical reaction rate was considered in soot oxidation. Soot formation and oxidation processes were modeled with the application of a hybrid method involving particle turbulent transport controlled rate and soot oxidation rate. Compared with the original soot model, the in-cylinder pressures, heat release rate and soot emissions predicted by this hybrid model agreed better with the experimental results. The verified hybrid model was used to investigate the effect of injection timing on engine performance. The results show that the new soot model predicted reasonable soot spatial profiles within the combustion chamber. The high temperature gas zone in cylinder for hybrid model case is distributed broadly soot and NOx emission dependence on the start-of-injection (SOI) timing. Retarded SOI timing increased the portion of diffusion combustion and the soot concentration increased significantly with retarding of the fuel injection timing. The predicted distributions of soot concentration and particle mass provide some new insights on the soot formation and oxidation processes in direct injection (DI) engines. The hybrid phenomenological soot model shows greater potential for enhancing understanding of combustion and soot formation processes in DI diesel engines.     

Effect of free stream turbulence on NOx and soot formation in turbulent diffusion CH4-air flames

A two-dimensional axisymmetric RANS numerical model was solved to investigate the effect of increasing the turbulence intensity of the air stream on the NOx and soot formation in turbulent methane diffusion flames. The turbulence–combustion interaction in the flame field was modelled in a k − ε/EDM framework, while the NO and soot concentrations were predicted through implementing the extended Zildovich mechanism and two transport equations model, respectively. The predicted spatial temperature gradients showed acceptable agreement with published experimental measurements. It was found that the increase of free stream turbulence intensity of the air supply results in a significant reduction in the NO formation of the flame. Such phenomenon is discussed by depicting the spatial distribution of the NO concentration in the flame. An observable reduction of the soot formation was also found to be associated with the increase of inlet turbulence intensity of air stream.     

Investigation of influence of detailed chemical kinetics mechanisms for hydrogen on supersonic combustion using large eddy simulation

Five detailed hydrogen combustion chemical kinetics mechanisms coupled with a partially stirred reactor (PaSR) combustion model were applied with large eddy simulation (LES) to study the influence of detailed mechanisms on supersonic combustion in a model scramjet combustor. The LES predictions of five detailed mechanisms for velocity, temperature, and combustor wall pressure show reasonable agreement with experimental results. Examining the effects on the distributions of temperature and species in supersonic combustion reveals that the supersonic flame structure is affected by detailed mechanisms. The different detailed mechanisms have a strong influence on the combustion efficiency, volume of the subsonic region, and subsonic combustion heat release rate in the combustor. Moreover, the total heat release in the computational domain for the five detailed chemical kinetics mechanisms is quite different. The subsonic combustion is dominant in the combustor for all detailed mechanisms. An analysis of the important reactions for H₂O, HO2, and OH is performed, revealing the reasons for differences in temperature and species distributions among the different detailed mechanisms in the combustor.     

加力燃烧室污染特性的大涡模拟

采用k方程亚网格尺度模型对模型加力燃烧室的污染特性进行大涡模拟研究，其中污染物CO亚网格尺度模型是以二步化学反应为基础，N0采用亚网格动力学模型，并用亚网格EBU燃烧模型估算化学反应速率，用热通量辐射模型估算辐射通量，通过数值计算结果与实验数据的比较，表明采用的亚网格污染物生成模型可以用于实际加力燃烧室污染物排放的预估．     

Theoretical and experimental investigations on the performance of dual fuel diesel engine with hydrogen and LPG as secondary fuels

The mathematical models to predict pressure, net heat release rate, mean gas temperature, and brake thermal efficiency for dual fuel diesel engine operated on hydrogen, LPG and mixture of LPG and hydrogen as secondary fuels are developed. In these models emphasis have been given on spray mixing characteristics, flame propagation, equilibrium combustion products and in-cylinder processes, which were computed using empirical equations and compared with experimental results. This combustion model predicts results which are in close agreement with the results of experiments conducted on a multi cylinder turbocharged, intercooled gen-set diesel engine. The predictions are also in close agreement with the results on single cylinder diesel engine obtained by other researchers. A reasonable agreement between the predicted and experimental results reveals that the presented model gives quantitatively and qualitatively realistic prediction of in-cylinder processes and engine performances during combustion.     

Numerical study of fuel temperature influence on single gas jet combustion in highly preheated and oxygen deficient air

Combustion of a single jet of propane in a cross-flowing stream of preheated and oxygen deficient air is numerically analyzed with emphasis on influences of fuel temperature. Both Eddy-Break-Up and PDF/mixture fraction combustion models coupled with RNG k–ε turbulent model were applied and the predicted results were compared. Thermal and prompt NO models were employed to calculate NO emissions. Results show that the Eddy-Break-Up model is more suitable for predicting temperature field and flame shape. It was showed that flame during high temperature air combustion condition is spread over a much larger volume. Flame volume increases with a reduction of oxygen concentration, and this trend is clearer if oxygen concentration in the preheated air is below 10%. Additionally, it is almost constant at fixed oxygen concentration and fuel inlet temperature for the temperature of the preheated and oxygen deficient air equal to 1041–1273 K. Increase of the fuel inlet temperature results in smaller flame, shorter mean residence time, smaller temperature peaks, and lower emission of NO.     

不同简化机理对高压直喷天然气船机燃烧和排放影响研究

基于三维CFD仿真软件模拟了高压直喷天然气船机的燃烧过程，探讨了四种不同简化程度机理对燃烧和排放的影响规律。结果表明：四种机理均能很好的预测高压直喷天然气船机在不同喷射时刻下的缸压和放热率。四个机理预测的燃烧相位和最高爆发压力随喷射时刻提前或推迟变化趋势一致；预测的不同燃烧相位的温度、当量比和NOx分布存在较小差异。但35步机理和27步机理预测的碳烟排放比334步机理和250步机理高。整体来看，受船机大尺度计算资源高限制，耦合简化的35步和27步机理的CFD模型预测的燃烧参数最大误差小于4.3%，预测的NOx排放最大误差小于12%，能够满足船机工程开发需求。