In advanced propulsion systems such as scramjet engines, endothermic decomposition of onboard large hydrocarbon fuels can be used effectively for cooling and active thermal protection. During the cooling process, large hydrocarbon fuels absorb heat and decompose into small fragments. Since fuel decomposition changes the chemical and transport properties of the reactants, it is expected to affect the combustion afterwards. In this study, forced ignition in quiescent n-decane/air mixtures with fuel decomposition is investigated via a simplified model and transient numerical simulations considering detailed chemistry and transport. The emphasis is placed on assessing the effects of fuel decomposition on ignition kernel development and minimum ignition energy (MIE) in both homogenous and fuel-stratified mixtures. Fuel decomposition is modelled by a homogeneous ignition process in n-decane/air mixture at constant atmospheric pressure and with an initial temperature of 1300 K. Small fragments appear during the pyrolysis process. The partially-reacted mixture is frozen and cooled to a lower temperature and used as the initial mixture in forced ignition. For homogeneous mixtures, fuel decomposition can greatly promote ignition for fuel-lean decane/air mixtures while it has little effect for the stoichiometric case. Fuel decomposition also affects the duration of unsteady ignition kernel transition. Besides, fuel decomposition and fuel stratification are combined to further promote forced ignition. New flame regimes are observed and an optimum stratification radius is identified. In order to promote the forced ignition, only the fuel within the optimum stratification radius needs to be decomposed. Furthermore, laser and spark ignition experiments are conducted to measure the MIE of n-decane/ethylene/air mixtures with different equivalence ratios and ethylene blending ratios. The MIE measured in experiments cannot be directly compared with simulation results since the simulation model for forced-ignition is simplified. Nevertheless, the experimental results are consistent with simulation results and thus validate some conclusions mentioned above. The present results provide useful guidance to the fundamental understanding of forced ignition in a mixture with fuel decomposition.

在超燃冲压发动机等先进推进系统中，机载大型碳氢化合物燃料的吸热分解可有效用于冷却和主动热保护。在冷却过程中，大型碳氢燃料吸收热量并分解成小碎片。由于燃料分解会改变反应物的化学和传输特性，因此预计会影响之后的燃烧。在这项研究中，通过考虑详细的化学和传输的简化模型和瞬态数值模拟，研究了燃料分解的静态正癸烷/空气混合物中的强制点火。重点是评估燃料分解对均质和燃料分层混合物中点火核发展和最小点火能 (MIE) 的影响。燃料分解通过正癸烷/空气混合物在恒定大气压和 1300 K 的初始温度下的均质点火过程建模。在热解过程中会出现小碎片。将部分反应的混合物冷冻并冷却至较低温度，并用作强制点火的初始混合物。对于均质混合物，燃料分解可以极大地促进贫燃料癸烷/空气混合物的点火，而对化学计量情况几乎没有影响。燃料分解也影响不稳定点火核转变的持续时间。此外，燃料分解和燃料分层相结合，进一步促进强制点火。观察到新的火焰状态并确定最佳分层半径。为了促进强制点火，只需要分解最佳分层半径内的燃料。此外，还进行了激光和火花点火实验以测量具有不同当量比和乙烯混合比的正癸烷/乙烯/空气混合物的 MIE。由于强制点火的仿真模型被简化，实验中测量的 MIE 不能直接与仿真结果进行比较。尽管如此，实验结果与模拟结果一致，从而验证了上述一些结论。目前的结果为对燃料分解混合物中强制点火的基本理解提供了有用的指导。进行激光和火花点火实验以测量具有不同当量比和乙烯混合比的正癸烷/乙烯/空气混合物的MIE。由于强制点火的仿真模型被简化，实验中测量的 MIE 不能直接与仿真结果进行比较。尽管如此，实验结果与模拟结果一致，从而验证了上述一些结论。目前的结果为对燃料分解混合物中强制点火的基本理解提供了有用的指导。进行激光和火花点火实验以测量具有不同当量比和乙烯混合比的正癸烷/乙烯/空气混合物的MIE。由于强制点火的仿真模型被简化，实验中测量的 MIE 不能直接与仿真结果进行比较。尽管如此，实验结果与模拟结果一致，从而验证了上述一些结论。目前的结果为对燃料分解混合物中强制点火的基本理解提供了有用的指导。实验结果与模拟结果一致，从而验证了上述一些结论。目前的结果为对燃料分解混合物中强制点火的基本理解提供了有用的指导。实验结果与模拟结果一致，从而验证了上述一些结论。目前的结果为对燃料分解混合物中强制点火的基本理解提供了有用的指导。