Abstract: To analyze the effects of fuel-air ratio on combustion modes more deeply，the flow-fields of scram. jet with different fuel-air ratio were acquired with experiment and CFD method. The method to calculate the heatrelease rate was presented. The CFD flow-fields were validated by experiments. With CFD results，a feedback bal. ance between heat release and flow velocity was presented，which can be used to explain the mechanism of com.bustion modes formation. Three combustion modes and their characteristics were presented. In scramjet mode，the heat release is distributed，the flow in combustor is supersonic，and there is no separation in isolator. In ramjet mode，the heat release is concentrated，the flow in combustor is subsonic，and there is large separation and strong shock train in isolator. In dual mode，the heat release is concentrated，in combustor the subsonic flow and super.sonic flow exist at the same time and there is large separation and strong shock train in isolator. Finally，a method to achieve scramjet mode under the condition of large fuel-air ratio was presented，that means putting a part of fu.el at the divergent part of the combustor to make sure the heat release is distributed.

Key words: Scramjet；Heat release rate；Combustion mode；Equivalence ratio

摘要： 为了深入分析当量比对燃烧模态的影响机理，通过试验和计算研究了不同当量比条件下超燃冲压发动机燃烧室流场，给出了释热速率的计算方法。结果表明，数值模拟结果具有一定的可靠性，并基于数值模拟结果，提出了模态形成过程中释热和流动速度的反馈平衡机理。给出了三种燃烧模态及其特征，超燃模态，燃烧释热为分布式，燃烧室流动速度为超声速，隔离段无分离；亚燃模态，燃烧释热为集中式，燃烧室流动为亚声速，隔离段存在大分离以及强激波串；混合模态，燃烧释热为集中式，燃烧室流动同时存在亚声速和超声速，隔离段存在大分离以及强激波串。提出了高当量比条件下实现超声速燃烧的方法，即在扩张段注油，避免集中式释热。

关键词: 超燃冲压发动机；释热速率；燃烧模态；当量比