TOWARD THE 50% BRAKE THERMAL EFFICIENCY: A 1D/3D NUMERICAL ANALYSIS OF AN ACTIVE PRE-CHAMBER FOR A SI HEAVY-DUTY GAS ENGINE

Innovative spark ignition heavy-duty engines with active pre-chamber combustion systems represent a promising and viable technology towards a marked reduction in pollutant emissions, with increased performance and reduced fuel consumption. Through a parallel and combined 1D/3D simulation methodology, cruise point and rated torque operating conditions were analyzed to assess the increase of brake thermal efficiency (BTE) under two ultra-lean conditions: air-to-fuel ratio equal to 1.7 and 1.9. The boundary conditions for the 3D-RANS numerical activity are provided by a 1D model of a single cylinder engine, properly calibrated according to experimental data detected by a large bore heavy-duty engine fueled by compressed natural gas (CNG). To evaluate the alignment between the two simulation platforms, the combustion process evolution, together with the turbulent flame propagation profiles obtained from 3D-CFD simulations, are used again iteratively in the 1D engine model to assess the in-cylinder pressures and heat release rate. A sensitivity analysis to the change in fuel percentage between pre-chamber and main-chamber was performed due to the deployment of a specific injection control logic. The characterization was then extended by performing an increasing compression ratio (CR) parameterization. Further insights to the variation of spark advance and the intake and exhaust pressure drop are proposed, for the evaluation of the most favorable conditions. The present analysis methodology revealed a detectable decrease in NOx emissions in view of the introduction of EURO VII regulations, and a comprehensive evaluation of the pre-chamber potential to reach 50% BTE target.