Combustion Modeling Lab at UC Berkeley

Current Research

Pre-ignition and detonation

Xian Shi, Je Ir Ryu (CML)

In conjuction with King Abdullah University of Science and Technology


While direct injection, high boost, and engine downsizing have shown great advantages in power density, fuel economy and emissions for modern internal combustion engines, a new engine knocking mode, super knock (also known as mega knock, etc.) may occur in boosted gasoline direct injection spark ignition (DISI) engines, primarily at low-speed, high-load operation conditions. The unexpected occurrence of super knock has become one of the major obstacles to advanced engine development as it can damage engine components catastrophically due to extremely high peak pressure and severe pressure oscillations. In general, the super knock is thought to be the result of pre-ignition events causing the end (unburnt) fuel/air mixtures to undergo a developing detonation or a deflagration to detonation transition (DDT). With modern visualization techniques, in-cylinder reaction front propagation speeds can be measured thus the detonation development has been captured in laboratory apparatus such as rapid compression machine, as well as in real engine. The project aims to improve the current understanding about:

1) The occurrence mechanism of engine pre-ignition and super knock events, including identification of reaction front propagation and end-gas combustion.

2) The fundamental physical process of detonation initiation and transition.

Both numerical and experimental investigations are conducted: Numerically, an 1-D compressible reacting flow solver ASURF-Parallel is used to simulate detonation events of highly reactive mixtures. Experimentally, pre-ignition engine experiments are performed by collaborators at KAUST.

Related papers

X. Shi, J. Ryu, J.-Y. Chen, R.W. Dibble, Modes of reaction front propagation and end-gas combustion of hydrogen/air mixtures in a closed chamber, Int. J. Hydrogen Energy 42 (2017) 10501-10512.

Engine combustion modesPressure traces of different combustion cycles in a pre-ignition engine.

End gas autoignitionNumerical simulation of end-gas detonation