Exploring the passive the pre-chamber ignition concept for spark-ignition engines fueled with natural gas under EGR-diluted conditions

The pre-chamber ignition system has demonstrated to be a suitable technology for increasing burning rates while reducing the cycle-to-cycle variability in spark-ignition engines. This concept offers an improvement in thermal efficiency through an increase in ignition energy and flame surface, allowing it to overcome knocking combustion issues at high engine load/speeds. This fact makes this ignition concept well compatible with the use of dilution strategies to control emissions or to further improve efficiency. However, despite promoting faster combustion, knocking combustion is still a major limitation at low rotational speeds and high engine loads (low-end torque). In this investigation, the performance of the passive pre-chamber concept is evaluated in a single-cylinder turbocharged spark-ignition engine fueled with compressed natural gas in EGR-diluted conditions. Several experiments and numerical simulations are combined to analyze the basis of the pre-chamber operation, while seeking to improve the global performance of the engine. To this end, a new pre-chamber geometry is proposed that is able to achieve better features in the ejected jets, to enhance the performance of the concept in the whole engine map.