Key Laboratory of Low-Grade Energy Utilization Technologies and Systems, Ministry of Education, School of Energy and Power Engineering, Chongqing University, Chongqing 400044, China.
Molecules. 2023 May 23;28(11):4273. doi: 10.3390/molecules28114273.
It has been discovered that there is a dynamic coupling between cycloalkanes and aromatics, which affects the number and types of radicals, thereby controlling the ignition and combustion of fuels. Therefore, it is necessary to analyze the effects of cyclohexane production in multicomponent gasoline surrogate fuels containing cyclohexane. In this study, a five-component gasoline surrogate fuel kinetic model containing cyclohexane was first verified. Then, the effect of cyclohexane addition on the ignition and combustion performance of the surrogate fuel was analyzed. This study shows that the five-component model exhibits good predictive performance for some real gasoline. Meanwhile, the addition of cyclohexane decreases the ignition-delay time of the fuel in the low and high temperature bands, which is caused by the early oxidation and decomposition of cyclohexane molecules, generating more OH radicals; in the medium temperature band, the isomerization and decomposition reactions of cyclohexane oxide cCHO dominate the temperature sensitivity of the ignition delay, affecting the small molecule reactions that promote the generation of reactive radicals such as OH, thus inhibiting the negative temperature coefficient behavior of the surrogate fuel. The laminar flame speed of the surrogate fuels increased with the increase in the proportion of cyclohexane. This is due to the fact that the laminar flame speed of cyclohexane is higher than that of chain and aromatic hydrocarbons, and the addition of cyclohexane dilutes the ratio of chain and aromatic hydrocarbons in the mixture. In addition, engine simulation studies have shown that at higher engine speeds, the five-component surrogate fuel containing cyclohexane requires lower intake-gas temperatures to achieve positive ignition and are closer to the in-cylinder ignition of real gasoline.
已经发现，环烷烃和芳烃之间存在动态耦合，这影响了自由基的数量和类型，从而控制了燃料的点火和燃烧。因此，有必要分析含有环己烷的多组分汽油替代燃料中环己烷生产的影响。在本研究中，首先验证了含有环己烷的五元组分汽油替代燃料动力学模型。然后，分析了环己烷的添加对替代燃料点火和燃烧性能的影响。研究表明，五元模型对一些实际汽油具有较好的预测性能。同时，环己烷的添加会降低燃料在低温和高温带的点火延迟时间，这是由于环己烷分子的早期氧化和分解，生成更多的 OH 自由基所致；在中温带，环己烷氧化物 cCHO 的异构化和分解反应主导着点火延迟的温度敏感性，影响促进 OH 等活性自由基生成的小分子反应，从而抑制替代燃料的负温度系数行为。替代燃料的层流火焰传播速度随环己烷比例的增加而增加。这是因为环己烷的层流火焰传播速度高于链烷烃和芳烃，而且环己烷的添加会稀释混合物中链烷烃和芳烃的比例。此外，发动机模拟研究表明，在较高的发动机转速下，含有环己烷的五元替代燃料需要较低的进气温度才能实现正向点火，并且更接近实际汽油的缸内点火。
