A quasi-dimensional model of pre-chamber spark-ignition engines

Increasingly stringent pollutant and CO2 emission standards require the car manufacturers to investigate innovative solutions to further improve the fuel economy of their fleets. Among these techniques, an extremely lean combustion has a large potential to simultaneously reduce the NOx raw emissions and the fuel consumption of spark-ignition engines. Application of pre-chamber ignition systems is a promising solution to realize a favorable air/fuel mixture ignitability and an adequate combustion speed, even with very lean mixtures. In this work, the combustion characteristics of an active pre-chamber system are experimentally investigated using a single-cylinder research engine. Conventional gasoline fuel is injected into the main chamber, while the pre-chamber is fed with compressed natural gas. In a first stage, an experimental campaign was carried out at various speeds, spark timings and air-fuel ratios. Global engine operating parameters as well as cylinder pressure traces, inside main combustion chamber and pre-chamber, were recorded and analyzed. Based on the available experimental data, a phenomenological model of this unconventional combustion system with divided combustion chambers was developed and validated. The model was then implemented in a 1D code. The proposed numerical approach shows the ability to simulate the experimental data with good accuracy, using a fixed tuning constant set. The model demonstrates to correctly describe the behavior of a pre-chamber combustion system under different operating conditions and to capture the physics behind such an innovative combustion system concept.