Development of Specific Tools for Analysis and Quantification of Pre-ignition in a Boosted SI Engine

Abstract

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.

Systematic Approach to Analyze and Characterize Pre-ignition Events in Turbocharged Direct-injected Gasoline Engines

“…In numerous technical publications potential root cause sources have been discussed [2,3,4,5,6,7,8]. Some track pre-ignition back to oil droplets and combustion chamber deposits as possible root cause [1, 5,12].…”

Using large-eddy simulation and multivariate analysis to understand the sources of combustion cyclic variability in a spark-ignition engine

“…In a context of increasingly stringent constraints on fuel consumption, CO 2 production, and pollutant emissions from road transport, it becomes crucial to be able to predict and control individual engine cycles, and thus to address the occurrence and effects of CCV. Engine technologies as downsizing [6,7], direct injection (DI) [8] or controlled auto-ignition (CAI) [9,10] are examples of technologies presently explored in order to reduce the CO 2 emissions from 2 future SIE. Yet the occurrence under certain operating conditions of excessive CCV when implementing these technologies is one of the factors limiting their practical performance or range of operation.…”

Simulations of engine knock flow field and wave-induced fatigue of a downsized gasoline engine

“…2-2(b), the in-cylinder knocking pressure suffered a huge oscillation with an amplitude of nearly 10MPa when the knock occurred initially and followed by a pressure fluctuation of gradually attenuating amplitude with an oscillation frequency of up to 10 kHz, and finally, this pressure is becoming steady. The impact of this knocking occurrence on the combustion chamber components fatigue is obvious [12].…”