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Recent developments on highly downsized spark ignition
engines have been focused on knocking behaviour
improvement and the most advanced technologies
combination can face up to 2.5 MPa IMEP while
maintaining acceptable fuel consumption. Unfortunately,
knocking is not the only limit that strongly downsized
engines have to confront. The improvement of low-end
torque is limited by another abnormal combustion which
appears as a random pre-ignition. This violent
phenomenon which emits a sharp metallic noise is
unacceptable even on modern supercharged gasoline
engines because of the great pressure rise that it causes
in the cylinder (up to 20 MPa).
The phases of this abnormal combustion have been
analysed and a global mechanism has been identified
consisting of a local ignition before the spark, followed by
a propagating phase and ended by a massive autoignition.
This last step finally causes a steep pressure
rise and pressure oscillations.
One of our objectives was to evaluate the sensitivity of
an engine to pre-ignition regarding its design and
settings. Therefore, in addition to our comprehension
work, we have developed a first methodology based
upon robust statistics to define new reliable and
repeatable criteria to quantify this stochastic pre-ignition
but also to detect each of its occurrence, suggesting the
possibility of an on-line detection during steady state and
transient operation as well. The statistical approach also
showed that the distributions of well chosen combustion
indicators are strongly altered by pre-ignitions. A second
methodology was then defined to evaluate the influence
of different parameters on pre-ignition by quantifying this
alteration. This analysis notably gives the opportunity to
achieve a deeper analysis of pre-ignition during engine
development on test bench.

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