On the role of top dead center conditions in the combustion phasing of homogeneous charge compression ignition engines

There is an inherent difficulty in trying to distinguish between the thermodynamic and the chemical effects in a homogeneous charge compression ignition (HCCI) engine. This article attempts to isolate the chemical kinetics effects in the framework of a zero-dimensional, thermo-kinetic model combined with a detailed chemical mechanism for iso-octane and an auto-ignition correlation. The study focuses on the behavior of single-stage ignition fuels near top dead center (TDC), as a means of relating conditions at TDC to predicted ignition timings. It is found that a unique relationship exists between combustion phasing, and the constant volume ignition delay at TDC conditions expressed in crank angle degrees ( CAD). This relationship holds for given engine parameters and composition over a wide range of RPM. For ignition near TDC, the ignition delay at TDC conditions expressed as a crank angle interval must be between 8 and 12 CAD, depending on engine design parameters.