正庚烷氧化基态OH基浓度时程吸收光谱诊断

Laser Absorption Spectrum Measurement of OH Concentration Time-Histories in n-heptane Oxidation

为了提供宽温度范围下正庚烷模型的微观验证数据,利用激波管反射激波方法结合紫外吸收光谱诊断技术,以OH基的A-X(0,0)跃迁R 1(5)谱线中306.6868 nm为中心诊断波长,测量了温度1197~1690 K、压力150 kPa、当量比1.0、燃料初始体积分数0.1%下,正庚烷/氧气/氩气混合气氧化过程中OH基浓度时程。结果表明,激波管真空度和漏气率是影响OH基浓度峰值的主导因素,结果分析中必须给予考虑以确保实验结果的准确性。实验观测到了正庚烷氧化过程OH基浓度时程演变的3种形态,发现入射激波引起的非理想物理边界层效应对OH基浓度时程测量影响显著。与已有的5个代表性正庚烷模型预测值比较发现,当前工况下模型可准确预测各温度下OH基浓度时程演变趋势,但各模型在同时预测宏观点火延迟和微观OH基浓度方面仍有缺陷,温度越低,各模型对点火延迟期的预测偏差越大。反应CH_(3)+HO_(2)=CH_(3)O+OH对正庚烷模型点火延迟预测性能影响较大,对该反应动力学参数的深入研究有助于完善正庚烷机理。

To provide microscopic validation data for n-heptane models over a wide temperature range,microsecond-resolved OH concentration time-histories were measured behind reflected shock waves in the oxidation of stoichiometric n-heptane(volume fraction of 0.1%)/O 2/Ar mixtures over the temperature(T 5)range of 1197-1690 K at the pressures(p 5)around 150 kPa.The OH time-histories were monitored by narrow-linewidth ring dye laser absorption near 306.7 nm at the well-characterized R 1(5)transition of the OH A-X(0,0)band.Results reveal that vacuum degree and leaking rates are the two dominant factors affecting peak value of the measured OH concentrations.Three morphologies of OH time-histories in n-heptane oxidation were observed,and the non-ideal physical boundary layer effect caused by incident shock wave shows a significant effect on OH concentration.Five commonly used mechanisms of n-heptane generally show acceptable predictions in the trend of OH time-histories at various temperatures,but are still not satisfactory in predicting both ignition delay time and OH time-histories simultaneously,and it shows that the lower the temperature,the greater the deviation between the model simulations and experimental measurements during induced ignition time.Reaction of CH_(3)+HO_(2)=CH_(3)O+OH has a great impact on the predictions in ignition delay times of n-heptane models,and further study on the kinetic parameters of this reaction is beneficial to refining the n-heptane models.