末端气体非常规燃烧与敲缸是制约高效增压汽油机和HCCI类内燃机技术发展的瓶颈。目前，人们尚不能十分清楚地解释内燃机(特别是处于极端工况下的新型内燃机)中非常规燃烧和敲缸的产生规律与机理。因此，针对新型内燃机高效燃烧技术研发中“非常规燃烧”这一核心科学问题，本项目采用数值模拟为主、理论分析为辅的研究方法，对高稀释率、贫燃、低温及高压极端条件下，由化学反应活性分层导致的非常规燃烧过程开展系统研究。本项目将发展涉及复杂反应机理燃烧过程的高效率、高精度数值模拟技术，获得化学反应活性分层导致的非常规燃烧模态的特征及产生条件，揭示低温与高温化学反应、压力波(激波)传播与壁面反射、以及湍流这几个关键物理化学因素对预混燃气自着火和非常规燃烧过程的耦合影响机制，在此基础上建立适用于内燃机工况的非常规燃烧模态定量判据。本项目旨在发展非常规燃烧方面的基础理论与算法，研究结果将为新型内燃机的设计优化提供科学依据。

Unconventional combustion in end gas and knock are severe constraints for the development of technologies of super-charging gasoline engines with high thermal efficiency and homogeneous charge compression ignition (HCCI) engines. However, the mechanisms of unconventional combustion and knock in internal combustion engines (ICEs), especially in the advanced ones under extreme conditions, have not been well understood. Therefore, motived by the key scientific problem of ‘unconventional combustion’ in the development of high-efficiency combustion technologies of advanced ICEs, the present project combines numerical simulation and theoretical analysis to comprehensively study the unconventional combustion processes induced by chemical reactivity stratification under extreme conditions (e.g., highly diluted, fuel-lean, low-temperature and high-pressure conditions). By developing highly efficient and highly accurate numerical computation methods for combustion process considering complex chemical mechanisms, the present project aims to identify the characteristics of different unconventional combustion modes induced by chemical reactivity stratification as well as the corresponding conditions. The coupling effects of various critical physical and chemical factors, including low-temperature and high-temperature chemistries, propagation and wall reflection of pressure wave or shock wave, and turbulence, on autoignition and unconventional combustion process in fuel-air mixtures, will be revealed. Based on that, quantitative criteria for different unconventional combustion modes under various conditions including those of ICEs will be established. The present project aims to develop fundamental theory and numerical computation methods on unconventional combustion. The results will provide scientific basis for the design and improvement of advanced ICEs.