基于液滴高压蒸发理论的变时滞燃烧室动力学建模与研究

为实现燃烧室组件的精确建模及其动力学特性的仿真研究,以零维时滞燃烧室模型为基础,考虑燃烧室内喷射、雾化、蒸发、混合、化学反应过程,采用针栓喷注器SMD(Sauter Mean Diameter,索特尔平均直径)经验关联式以及液滴高压蒸发理论对液氧/甲烷推进剂组合的燃烧时滞进行求解,建立了基于液滴高压蒸发理论的变时滞燃烧室模型。基于1 kg/s级推力室开展热试车验证了变时滞燃烧室模型的准确性,结果表明:所建立的变时滞燃烧室模型可以较为准确地预测燃烧室的压力以及温度动态响应过程,与试验结果相比,稳态压力以及温度误差均在6%以内,压力参数动态响应时间的误差在14%以内,仿真结果具有较高的精度。基于变时滞燃烧室模型开展仿真研究,研究发现:液氧液滴初始粒径以及燃烧室温度作为影响液氧液滴寿命的主要因素,主导着液氧时滞的变化;变时滞模型可以根据工况参数动态计算推进剂燃烧时滞,启动初期喷注器雾化效果较差,液滴最大粒径达到800μm,且燃烧室温度低,进而导致燃烧时滞偏大,最大达到了1100 ms,约为稳定工作状态下燃烧时滞的40倍。本文所建立的变时滞燃烧室模型可根据工况参数对燃烧时滞进行动态计算,相较于传统时滞模型,其燃烧时滞的变化趋势更符合发动机实际工作过程,同时其室压的响应时间、稳态值也更接近实验值,该模型未来可为实际发动机时序设计等提供仿真支撑。

A new stationary droplet evaporation model and its validation

The liquid droplet evaporation character is important for not only combustion chamber design process but also high-accuracy spray combustion simulation. In this paper, the suspended droplets＇ evaporation character was measured in a quiescent high-temperature environment by micro high-speed camera system. The gasoline and kerosene experimental results are consistent with the reference data. Methanol, common kerosene and aviation kerosene droplet evaporation characteristics, as well as their evaporation rate changing with temperature, were obtained. The evaporation rate experimental data were compared with the prediction result of Ranz-Marshall boiling temperature model（RMB）, Ranz-Marshall low-temperature model（RML）, drift flux model（DFM）, mass analogy model（MAM）, and stagnant film model（SFM）. The disparity between the experimental data and the model prediction results was mainly caused by the neglect of the natural convection effect, which was never introduced into the droplet evaporation concept. A new droplet evaporation model with consideration of natural convection buoyancy force effect was proposed in this paper. Under the experimental conditions in this paper, the calculation results of the new droplet evaporation model were agreed with the experimental data for kerosene, methanol and other fuels, with less than 20% relative deviations. The relative deviations between the new evaporation model predictions for kerosene and the experimental data from the references were within 10%.

考虑自然对流的厚交换层液滴蒸发模型及其检验

两相模型对航空发动机燃烧室数值模拟的准确性至关重要,液体燃料的蒸发特性是两相模型的一个关键因素,为了得到准确合理的两相模型从而为燃烧室的设计提供依据,采用悬滴法实验研究了甲醇、煤油及航空煤油液滴在静止环境下的高温蒸发现象,并得到了液滴蒸发速率随环境温度的变化规律。比较实验数据与已有液滴蒸发模型计算结果,发现二者具有较大差距,分析认为已有模型应该考虑静止环境中自然对流对液滴蒸发的影响。在前人工作基础上,用考虑自然对流浮升力因素的厚交换层理论对静止环境下液滴的高温蒸发进行理论推导,得到新的蒸发模型。采用本文实验结果及文献液滴蒸发实验数据对新模型进行了检验。对于甲醇和煤油,在本文的实验工况下,新模型计算结果与实验结果具有较好的一致性,与实验的相对偏差不超过20%;对于煤油,新模型计算结果与文献实验结果的相对偏差不超过10%。