On the Nature of Autoignition Leading to Knock in HCCI Engines

There is worldwide interest in developing Homogeneous Charge Compression Ignition concepts for lean burn/heavily diluted, low emissions, combustion engines. Although there has been much work and considerable progress relating to autoignition onset in such engines, there has been relatively little study of the reasons for the knock which limits their operation at high power. Building on earlier work on end gas autoignition development and knock in spark ignition engines, it is suggested that the problem is rooted in the mode of autoignition. The conditions supporting the most violent “developing detonation” mode, with increasing charge dilution, bulk unburned gas temperature level and local temperature gradient are explored in relation to HCCI engines.