Numerical Simulations of Pre-Chamber Induced HCCI Combustion (PC-HCCI)

Advanced combustion concepts that rely on the lean-burn approach are a proven solution for increasing the efficiency and reducing the harmful emissions of SI engines. The pre-chamber spark ignited (PCSI) engines utilize high ignition energy of the multiple jets penetrating from the pre-chamber, to enable fast and stable combustion of lean mixture in the main chamber. The combustion is still governed by the flame propagation, so the dilution level and efficiency benefits are highly restricted by strong decrease of laminar flame speeds. Homogeneous charge compression ignition (HCCI) combustion allows a higher dilution level due to rapid chemically driven combustion, however the inability to directly control the ignition timing has proven to be a major setback in HCCI deployment. The addition of the spark plug, to improve the controllability and widen the operating range, resulted in a combustion concept known as spark-assisted compression ignition (SACI), however spark ignition of lean mixtures is very difficult even at close to HCCI conditions. Since one of the features of active pre-chamber is the ability to control mixture dilution at the spark plug location, a combustion concept called pre-chamber induced HCCI combustion (PC-HCCI) that combines pre-chamber ignition and HCCI combustion is proposed. In this concept a near stoichiometric mixture in the pre-chamber is spark ignited and the combustion in pre-chamber triggers kinetically controlled combustion of lean main combustion chamber mixture. As a first step of the research, numerical modelling of the proposed combustion concept is made by employing 3D-CFD and 1D/0D simulation models. The main purpose of the modelling is to define main geometrical and operating parameters required for achieving a pre-chamber induced HCCI combustion and to predict possible benefits of employing such combustion concept.