Characterization of the Ignition and Early Flame Propagation of Pre-Chamber Ignition System in a High Pressure Combustion Cell

The Pre-Chamber spark plug, already in its most simple configuration, allows a cycle
fuel consumption reduction of 2-3% (WLTC) by enabling a significant compression ratio
increase due to its huge knock mitigation effect. This benefit can be strongly extended
in the homogeneous lean burn operation mode with very low nitrogen oxide
emissions by a novel approach of injecting a well prepared fuel-air-mixture inside the
Pre-Chamber. An increase of the engine compression ratio allows further the development
of a new combustion process referred as the Pre-Chamber supported self-ignition
process, which enable an increased thermodynamic efficiency at part load operating
points of a gasoline engine.
The development of a suitable Pre-Chamber ignition system requires the technical understanding
of the Pre-Chamber geometry parameters on the combustion process.
The impact of the overflow channel design on the flame propagation and ignition of the
fuel-air mixture inside the main chamber must be understood in greater detail. This in
turn requires a high-fidelity combustion model which is capable of predicting the impact
of the overflow channel geometry on e.g. ... mehrflame extinction, radical recombination on
the walls of the Pre-Chamber orifice and finally the behavior of main chamber inflammation
regardless of the Pre-Chamber ignition regime.
Focus of this work is to discuss the impact of the Pre-Chamber geometry onto the
inflammation and early flame propagation inside the main combustion chamber by
means of experiments in an optical high pressure vessel under simplified boundary
conditions. As a basis, the simultaneous high speed measurement of Schlieren and
OH* chemiluminescence serve as a fundamental means to analyze ignition performance
and early flame propagation in order to develop and validate an accurate combustion
model.
Initially, the general impact of the chamber pressure will be discussed emphasizing
specifically on the differences between certain Pre-Chamber layouts and the conventional
ignition system onto flame speed and ignition probability. Furthermore, variations
of e.g. the number of overflow holes, the orifice diameter and the volume of the Pre-
Chamber aids to identify the most relevant parameters responsible for flame extinction
and combustion performance inside the main chamber.