肼类燃料与NO_(2)气相抽氢的反应动力学模拟

Kinetics of Gas Phase Hydrogen Extraction from Hydrazine Fuels with NO_(2)

为了分析肼类燃料与NO_(2)气相反应过程中着火延迟期的影响因素,采用密度泛函理论对反应过程进行了模拟,主要对肼(N2H4)、甲基肼(MMH)与偏二甲肼(UDMH)3种肼类燃料的反应活性、活性位点以及抽氢反应过程的势能面与反应速率常数进行了计算。结果表明,3种肼类燃料中UDMH的最高占有轨道与最低空轨道能量差最小,为0.20522 eV,表明UDMH的活性最大,因此与NO_(2)反应的最快,符合其着火延迟期最短的特性;确定了3种肼类燃料的活性位点,N_(2)H_(4)活性位点为N(1)或N(4),MMH活性位点为N(1),UDMH活性位点为N(1);对3种肼类燃料的反应活性位点进行抽氢反应的计算,UDMH的反应势垒最小,为3.589 kJ·mol^(-1),反应速率常数最大,为9.81×10^(5)L·s^(-1)·mol^(-1),符合其着火延迟期最短的特性,得出在肼类燃料中,与NO_(2)反应的抽氢反应势垒越小,反应速率常数越大,着火延迟期越短。

In order to analyze the factors affecting the ignition delay time in the gas phase reaction process between hydrazine fuel and NO_(2),the reaction process was simulated by using density functional theory.The reaction activities,active sites,potential energy surfaces and reaction rate constants in hydrogen extraction reaction process of hydrazine(N_(2)H_(4)),methyl hydrazine(MMH)and unsymmetrical dimethyl hydrazine(UDMH)were calculated.The results showed that the energy difference between the highest occupied orbital and the lowest vacant orbital of UDMH was the smallest among the three hydrazine fuels,which was 0.20522 eV,indicating that UDMH had the highest activity,so it has the fastest reaction rate with NO_(2),which in line with the characteristic of the shortest ignition delay time.The active sites of three hydrazine fuels were identified,N(1) or N(4) for N_(2)H_(4),N(1) for MMH and N(1) for UDMH.The active sites of hydrogen extraction reaction of three hydrazine fuels were calculated,it was found that the reaction barrier of UDMH is the smallest,which is 3.589 kJ·mol^(-1),and the reaction rate constant is the largest,which is 9.81×10^(5) L·s^(-1)·mol^(-1),which is consistent with the shortest ignition delay time,it is concluded that in hydrazine fuel,the smaller the hydrogen extraction reaction barrier with NO_(2),the larger the reaction rate constant,and the shorter the ignition delay time.