RANS Based Multidimensional Modeling of an Ultra-Lean Burn Pre-Chamber Combustion System with Auxiliary Liquid Gasoline Injection

Evolving emissions and fuel efficiency legislation has driven the development of ultra-lean burn engine concepts that combine high efficiency with low criteria emissions, including nitrogen oxides (NO_x). Traditional spark ignition (SI) systems have limitations in terms of available ignition energy and its distribution. Turbulent Jet Ignition (TJI) is a pre-chamber-based combustion system that enables ultra-lean operation through high energy jets acting as a distributed ignition source. Combustion is initiated in the pre-chamber (with or without auxiliary fuel injection) using a spark plug. The resulting flame is quenched in the pre-chamber nozzle thereby generating chemically active turbulent jets which penetrate and reignite in the main-chamber at multiple points after a time delay.

In this current work a Reynolds-averaged Navier-Stokes (RANS) based multidimensional model was developed and validated for the auxiliary fuel injected TJI combustion system using commercially available CONVERGE CFD code. The modeled system operates solely on gasoline fuel in which the main combustion chamber is inducted with ultra-lean (λ∼1.8) premixed charge while the pre-chamber is directly injected with liquid gasoline, creating locally rich conditions in the pre-chamber at the time of spark. Detailed chemistry is used to model the combustion directly by adopting a 38-species, 69 reaction gasoline surrogate (iso-octane) skeletal reaction mechanism. Predictions are compared to experimental data from a production based single-cylinder thermodynamic engine under naturally-aspirated and boosted conditions at 2500 rpm engine speed. The correlated operating points include various compression ratios and pre-chamber designs. Analysis results highlight the effect of internal flow features within the pre-chamber on the mixture preparation process past the direct injection event. Turbulent jets issued via the nozzles from the pre-chamber are quantitatively analyzed as they enter and exit the nozzles. The main chamber reignition process is analyzed by investigating the predicted jet shapes along with the temperature and species profiles within the jets.