A Quasi-Dimensional Model of Pre-Chamber Spark-Ignition Engines

Increasingly stringent legislations are inducing the car manufacturers to investigate innovative solutions to improve the vehicle fuel economy. Some of them act on the vehicle/engine interaction, such as the powertrain electrification, while other techniques directly affect the engine thermal efficiency. Among them, concerning the spark-ignition engines, a lean combustion showed the potential to improve the fuel consumption. This approach, on the other hand, causes some drawbacks, such as a combustion stability worsening and the impossibility for the TWC to optimally operate. A pre-chamber ignition system could represent an interesting solution to overcome the above issues. Especially in the case of an active system, a high fuel-air mixture ignitability, and an adequate combustion speed can be obtained even with a very lean mixture. In this work, a research single-cylinder SI engine equipped with an active pre-chamber is analyzed. A conventional gasoline fuel is injected in the main chamber while the pre-chamber is fed with CNG. In a first stage, an experimental campaign is carried out under various operating conditions, at various speeds, spark timings and air-fuel ratios. Both global engine parameters and pressure cycles, inside the cylinder and pre-chamber, are measured. A phenomenological model of such unconventional combustion system has been developed and validated by using the experimental data. The model is implemented in a 1D code. The proposed numerical approach shows the ability to simulate the experimental data with a good accuracy, with a fixed tuning constant set. The model hence proves to correctly describe the behavior of a pre-chamber combustion system under different operating conditions, demonstrating the capability to capture the physics behind such innovative concept.