The effect of energy intensification on the formation of severe knock in internal combustion engines

摘要

With the demand of high efficiency, IC (internal combustion) engines have been pushed to their thermodynamic limits. As a result, severe knock occurs which would make a huge destruction to engine parts. Detonation is found to be the essence of such severe knock. In this research, a series of numerical simulations were conducted to prove that the detonation only occurs in the small clearance chamber while hardly occurs in the large clearance chamber, which is also validated by the detonation bomb experiments. If study the pressure profiles carefully, the shock wave intensification phenomenon can always be found before the severe knock event, which is found to be a reason for the detonation formation. Such intensification phenomenon is mainly caused by three mechanisms: separately the wave-secondary flame, wave-wave and wave-boundary wall interacting mechanism. Through the analysis of the detailed chemical reaction mechanisms of H-2/O-2, the shock wave intensification caused by the wave-secondary flame interacting mechanism is revealed, which would occur both in the small and the large clearance chamber. Therefore, the key factors to decide whether the severe knock would occur are attributed to the wave-wave and the wave-wall interaction. According to numerical study, it's found that the chamber shape would affect both the wave-wave and the wave-wall interaction, which would decide the shock wave energy in the edge region. Once the energy of the shock wave is intensified to a critical level, the detonation as well as the severe knock would be formed.