富氢重整气对天然气发动机燃烧反应过程的影响

为研究基于废气重整再循环(REGR)技术的天然气发动机燃烧排放调控机制,开展了富氢重整气添加对点燃式天然气发动机缸内燃烧过程影响的数值模拟研究。结果表明,添加富氢重整气与增大过量空气系数对天然气发动机的燃烧过程的影响规律相反。增大重整气添加率可使燃料着火时刻提前1.42°,燃烧持续期缩短;增大过量空气系数则会使缸内平均压力峰值和放热率峰值降低,着火时刻滞后2.24°。REGR率增加到16%时可使总碳氢化合物排放降低26.98%,NO x排放降低62.52%,但会导致发动机功率降低9.52%。基于此,从化学动力学角度进一步解析REGR率对天然气发动机缸内燃料燃烧反应过程与污染物生成演化过程的影响。结果表明,随REGR率增大,OH自由基参与CH 4消耗反应占比增大,从而加快基元反应速率,使燃烧相位提前,并使未燃HC排放降低。

固液发动机燃面退移控制因素分析

为获得固液发动机固体燃料燃面退移的控制因素和机理,开展了数值仿真和试验研究。建立二维轴对称计算模型,考虑燃料与氧化剂的混合燃烧和流动过程,计算得到了固液发动机工作过程中的温度、压强、速度和组分的分布,以及不同时刻固体燃料的燃面形貌。仿真与试验结果的对比证明了计算方法的有效性。结果表明:固液发动机的燃面呈现显著的非平行退移特征;燃烧室压强对燃面退移不均匀性的影响可忽略;控制燃面退移的主要因素是燃气传向固体燃料表面的热流密度,燃料表面的温度变化是宏观表现。在靠近喷嘴位置,燃面退移的热量传递主要受燃烧反应过程控制,而靠近喷管处燃面退移的热量传递主要受燃气流动过程控制。研究为固液发动机的装药优化设计和高效燃烧组织提供了理论依据。

Simulation of Catalytic Combustion of Methane in a Monolith Honeycomb Reactor

Catalytic combustion of CH4/air in monolith reactor is simulated using a commercial computational fluid dy-namic code. The user subroutines to describe the heterogeneous reaction at the channel wall in a single channel and at the channel walls in the whole reactor are incorporated into the program. The correctness of the method is verified by com-paring the simulation results with the experimental data for the whole reactor. Furthermore, it is observed that the model based on the whole reactor is more reasonable than that based on a single channel. Therefore, using the former, the effects of operating conditions such as inlet gas velocity, temperature, concentration and catalyst loading on methane conversion are investigated.

Modelling of Turbulent Nonpremixed CH4/H2 Flame Using Second-Moment Turbulence Closure Models

Turbulent nonpremixed CH4/H2 flame has been simulated using several typical differential secondmoment turbulence closure (SMTC) models. To clarify the applicability of the various models, the LRR-IP model,JM model, SSG model as well as two modified LRR-IP models were tested. Some of above-mentioned SMTC models cannot provide the overall satisfactory predictions of this challenging case. It is confirmed again that the standard LRR-IP model considerably overpredict the centerline velocity decay rate, and therefore performs not well. Also it is interesting to observe that the JM model does not perform well in this challenging test case, although it has already been proved successful in other cases. The SSG model produces quite satisfactory prediction and performs equally well or better than the two modified LRR-IP models in the reacting case. It can be concluded that the modified LRR-IP models as well as the SSG model are superior to the other SMTC models in the turbulent nonpremixed CH4/H2 flame.

Coupled simulation of recirculation zonal firebox model and detailed kinetic reactor model in an industrial ethylene cracking furnace

A coupled system simulating both firebox and reactor is established to study the naphtha pyrolysis in an industrial tubular furnace.The firebox model is based on zone method including combustion,radiation,and convection to simulate heat transfer in the furnace.A two-dimensional recirculation model is proposed to estimate the flow field in furnace.The reactor model integrates the feedstock reconstruction model,an auto-generator of detail kinetic schemes,and the reactor simulation model to simulate the reaction process in the tubular coil.The coupled simulation result is compared with industrial process and shows agreement within short computation time.

A novel model for cost performance evaluation of pulverized coal injected into blast furnace based on effective calorific value

The combustion process of pulverized coal injected into blast furnace involves a lot of physical and chemical reactions. Based on the combustion behaviors of pulverized coal, the conception of coal effective calorific value representing the actual thermal energy provided for blast furnace was proposed. A cost performance evaluation model of coal injection was built up for the optimal selection of various kinds of coal based on effective calorific value. The model contains two indicators: coal effective calorific value which has eight sub-indicators and coal injection cost which includes four sub-indicators. In addition, the calculation principle and application of cost performance evaluation model in a Chinese large-scale iron and steel company were comprehensively introduced. The evaluation results finally confirm that this novel model is of great significance to the optimal selection of blast furnace pulverized coal.

Numerical study on catalytic combustion of methane with ozone using Pd-exchanged zeolite X

A steady-state ID macro-homogeneous model is developed to illustrate the combustion process of methane with ozone in the reactor composed of Pd-exchanged zeolite X. The model is validated by comparing the predicted results with the measured data. The methane conversion increases with decreasing the inlet methane concentration and gas space velocity and increasing the inlet ozone concentration and temperature. As the reactor length reduces, the methane conversion varies little if the reactor is too long but decreases when the reactor is too short. Therefore, the reactor should he properly designed to balance costs and the methane-conversion efficiency.