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贫油燃烧过程中很容易产生振荡燃烧现象,而振荡燃烧则会进一步影响燃烧室中氮氧化物(nitrogen oxides,NOx)的生成与排放。为了研究振荡燃烧的触发机制及其对NOx生成与排放的影响,利用FLUENT中的离散相模型、非预混燃烧模型和混合分数/PDF平衡化学反应模型,对贫油直喷燃烧室内的航空煤油/空气非预混燃烧进行了大涡数值模拟,亚网格模型采用WALE模型。将计算与实验值进行比较发现:在喷嘴附近区域,数值结果与预测结果略有差异,在其他区域,数值计算的各个物理参量值都与实验值非常吻合。通过改变入口空气流速,触发了振荡燃烧,其主频为560和1200Hz。对燃烧稳定性的模拟表明,可以通过调整燃烧室的入口条件来激励或者抑制振荡燃烧现象的出现。在此基础上分别计算了稳定燃烧和不稳定燃烧时的NOx排放,结果表明振荡燃烧现象的出现明显改变了NOx的生成与排放。
Oscillation combustion can easily occur during lean burn combustion, and oscillation combustion further affects the generation and emission of nitrogen oxides (NOx) in the combustion chamber. In order to study the triggering mechanism of oscillating combustion and its impact on the formation and emission of NOx, using the discrete phase model in FLUENT, the non-premixed combustion model and the mixed fraction / PDF equilibrium chemical reaction model, / Air non-premixed combustion large-eddy numerical simulation, sub-grid model using WALE model. Comparing the calculated results with the experimental results, it is found that there is a slight difference between the numerical results and the predicted results in the vicinity of the nozzle. In other areas, the numerical values of the physical parameters are in good agreement with the experimental values. Oscillatory combustion was triggered by changing the inlet air flow rate at 560 and 1200 Hz. Simulations of combustion stability show that the occurrence of oscillatory combustion can be stimulated or suppressed by adjusting the inlet conditions of the combustion chamber. On this basis, the NOx emissions of stable combustion and unstable combustion were respectively calculated. The results show that the appearance of oscillatory combustion obviously changes the generation and emission of NOx.