A Quasi-Dimensional Model of Pre-Chamber Spark-Ignition Engines
To be published on April 2, 2019 by SAE International in United States
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.