  The advancement of highly boosted internal combustion engines (ICEs) with
high thermal efficiency is mainly constrained by knock and super-knock
respectively due to the end gas autoignition and detonation development. At the
end of the compression stroke, the pressure wave propagation and reflection in
a small confined space may greatly influence the end gas autoignition, leading
to different autoignition characteristics from those in a large or open space.
The present study investigates the transient autoignition process in an
iso-octane/air mixture inside a closed chamber under engine-relevant
conditions. The emphasis is given to the assessing effects of the pressure
wave-wall reflection and the mechanism of extremely strong pressure
oscillations typical for super-knock. It is found that the hot spot induced
autoignition in a closed chamber can be greatly affected by shock/pressure wave
reflection from the end wall. Different autoignition modes respectively from
the hot spot and end wall reflection are identified. A non-dimensional
parameter quantifying the interplay between different length and time scales is
introduced, which helps to identify different autoignition regimes including
detonation development near the end wall. It is shown that detonation
development from the hot spot may cause super-knock with devastating pressure
oscillation. However, the detonation development from the end wall can hardly
produce pressure oscillation strong enough for the super-knock. The obtained
results provide a fundamental insight into the knocking mechanism in engines
under highly boosted conditions.
