在发动机高温升、高压比的发展趋势下，燃烧室内不再是单一的自着火模式或火焰传播模式，而是两者相互耦合，这给发动机的稳定燃烧带来了很大挑战。因此，自着火与火焰传播的耦合，即自着火协助下的火焰传播，是发动机安全运行的关键问题之一。然而，火焰传播模式从无自着火协助到有自着火协助的转变规律、自着火协助下的火焰传播特性等研究尚不完善。对此，本文通过实验、数值模拟和理论分析，针对自着火协助下的层流火焰传播特性进行了深入研究。 首先，针对清洁燃料合成气（CO、H2），开展了定压球形火焰实验，分析了基于数值模拟的映射方法，并将其系统地用于球形火焰实验中。研究发现，映射法对化学反应动力学参数的敏感性较低，比较映射法与经典外推法的结果得到：当量比越大，燃料中氢气含量越小，两种方法获得的层流火焰速度差异越小；针对非线性较强或火焰半径范围较小的情况，映射法能显著降低层流火焰速度的不确定度。 然后，针对发动机替代燃料（正庚烷、航空煤油Jet-A、正十二烷），对自着火协助下的火焰传播进行了数值模拟和理论研究。通过对火焰传播速度与火焰结构的分析，揭示了火焰传播从无自着火协助到有自着火协助的转变规律：随停留时间增大，火焰传播速度先缓慢增大，而后在接近自着火延迟时间时急剧增大，同时高温反应区从反应-扩散平衡逐步转变为反应-对流平衡。进一步地，与小分子燃料不同，对具有两阶段着火特性的大分子燃料，火焰传播速度随停留时间的变化会出现过冲现象，导致已有的火焰传播速度与停留时间的标度律不再成立。基于此，本文提出了火焰传播速度与重要组分浓度的新标度律，并在较宽范围的温度、压力、当量比条件下，对小分子燃料和发动机大分子燃料进行了验证。此外，在考虑详细化学反应动力学的基础上，提出了自着火协助下的火焰传播速度模型，该模型能良好预测火焰传播速度并刻画燃料两阶段自着火的协助效应，揭示了自着火协助作用主要来源于未燃物温度的升高。 最后，研究了典型发动机工况下，掺氢对航空燃油替代燃料（正十二烷）自着火与火焰传播特性的影响。计算结果表明，在典型的亚音速巡航工况下，氢气抑制自着火；而在超音速巡航工况下，氢气的抑制/促进作用取决于具体工作温度和掺氢量。对于自着火协助下的火焰传播，掺氢会显著提高火焰传播速度，但由于氢气不具有低温化学反应，因此会减弱甚至消除正十二烷第一阶段自着火的协助效应。

Under the trend of the high-temperature rise and high-pressure ratio in gas turbines, the combustion mode in the combustion chamber is not merely autoignition or flame propagation, but a couple of the two, which brings great challenges to the engine stability. Therefore, autoignition-assisted flame propagation is one of the key issues for engine safety. However, studies on the transition from flame propagation to autoignition-assisted flame propagation and autoignition-assisted flame propagation characteristics are inadequate. In this dissertation, the propagation characteristics of autoignition-assisted laminar flames are thoroughly studied through experiments, numerical simulations, and theoretical analysis. Firstly, the laminar flame speeds of the clean fuel syngas (CO and H2) were measured using the constant pressure dual-chamber apparatus. The new mapping method based on numerical simulation is analyzed and applied to spherical flame experiments, and the results show that the mapping method is not sensitive to the chemical kinetic parameters. Comparing the results from the mapping method and traditional extrapolation method, it is found that the larger the equivalence ratio or the smaller the hydrogen content in the unburnt mixture, the smaller the laminar flame speed difference obtained by the two methods. In addition, for flames with strong nonlinearity or with a small flame radius range, the mapping method can notably reduce the flame speed uncertainty. Then, the autoignition-assisted freely propagating flames of alternative engine fuels (n-heptane, Jet-A, n-dodecane) were numerically simulated and theoretically studied. In terms of flame propagation speed and flame structure, the transition law from flame propagation to autoignition-assisted flame propagation is revealed. Results show that with the increases of residence time, the assistance of autoignition is enhanced, and a sharp increase is observed in the flame propagation speed when approaching the ignition delay time. Meanwhile, the balance in the high-temperature reaction zone gradually transforms from diffusion-reaction balance to convection-reaction balance. Furthermore, different from the simple fuels, for complex hydrocarbon fuels with two-stage ignition characteristics, there exists an overshoot in the residence time, which means the previous scaling between the flame propagation speed and the residence time breaks down. Thus, a new scaling between the flame propagation speed and the important component concentration is proposed and further verified under a wide range of temperatures, pressures, and equivalence ratios for both simple and complex fuels. In addition, an analytical model, which considers detailed chemistry, is proposed to predict the autoignition-assisted flame propagation speed. The model can depict the two-stage autoignition assistance and the good agreement with the one-dimensional calculation results implies that the autoignition assistance mainly comes from the temperature rise of the unburnt mixture. Finally, the effects of hydrogen addition on the autoignition and flame propagation characteristics of n-dodecane, a surrogate jet fuel, were numerically investigated at typical engine conditions. Results show that hydrogen acts as an inhibitor under subsonic cruise conditions while either an inhibitor or an accelerator under supersonic cruise conditions depending on the temperature and hydrogen content. In addition, for autoignition-assisted flames, the hydrogen addition can significantly increase the flame propagation speed but alleviate or even eliminate the first-stage autoignition assistance due to the absence of low temperature chemistry.