贫预混燃烧室化学反应器网络模型建模及不确定性分析

基于CFD三维数值模拟结果的化学反应器(CRN)网络模型方法具有快速预估燃烧室NOx排放的特点。研究通过CFD数值模拟手段获得了贫预混燃烧室流场、温度场等特征分布,基于燃料空气掺混特性、速度场、温度场、OH分布以及达姆科勒数,燃烧室被离散划分为预热区、火焰锋面区、火焰过渡区、后火焰区、中心回流区以及角回流区,建立了复杂的CRN模型表征燃烧室内部的流动特征和火焰结构。以贫预混燃烧器为对象,与实验结果进行了对比验证。通过敏感性和不确定性分析获得了反应区域停留时间和烟气回流比例等关键参数对NOx排放的影响规律。结果表明:CFD-CRN混合方法更适用于在高当量比条件下贫预混燃烧室NOx排放的快速有效预测。在相同扰动强度的条件下,反应预热区域和火焰锋面区域的停留时间扰动对CRN模型预测NOx的生成量和稳定性影响更显著。CFD-CRN混合方法应明确在较高的绝热火焰温度条件下烟气回流比的准确性计算及其对NOx生成的显著影响。 

Modeling and uncertainty analysis of chemical reactor network model in lean premixed combustion chamber

The chemical reactor network (CRN) model based on three-dimensional numerical simulation results of CFD has great advantage in fast and accurate prediction of NOx emissions for combustor. In this work, the characteristic distributions of flow and temperature fields in a lean premixed combustor were simulated using CFD method. The combustor was separated in several regions, includingpreheating region, flame front region, flame transition region, post flame region, central recirculation region and corner recirculation region, based on the fuel-air blending characteristics, velocity field, temperature field, OH distribution, and Damkohler number. A complex CRN model was established to characterize the flow characteristics and flame structure inside the combustion chamber. The preliminary verification of CRN model was performed with experimental data of lean premixed burner. The effects of several crucial parameters, including the residence time and the flue gas recirculation ratio, on NOx emission were analyzed through sensitivity and uncertainty analysis. The CFD-CRN hybrid method can quickly and effectively predict the NOx production of the lean premixed combustor under high equivalence conditions. The residence time disturbances of preheating zone and the flame front zone have more significant effects on emissions and stability of NOx prediction of CRN models under the same disturbance intensity. The flue gas recirculation ratio of CFD-CRN method should be accurately calculated under high adiabatic flame temperature, which has significant effect on NOx formation.