Enhanced Multi-Zone Model for Medium Pressure Injection Spray and Fuel-Wall Impingement in Light-Duty Diesel Engines

Nowadays the high competition reached by the automotive market forces Original Equipment Manufacturers (OEMs) towards innovative solutions. Strict emission standards and fuel economy targets make the work hard to be accomplished. Therefore modern engines feature complex architecture and embed new devices for Exhaust Gas Recirculation (EGR), turbocharging (e.g. multi-stage compressors), gas after-treatment (e.g. the Selective Catalyst Reduction (SCR)) and fuel injection (either high or low pressure). In this context the Engine Management System (EMS) plays a fundamental role to optimize engine operation. The paper deals with fuel spray and combustion simulation by a multi-zone phenomenological model aimed at the steady-state optimal tuning of the injection pattern. The fuel spray model simulates the fuel-air mixture formation, the in-cylinder gas mixture evolution and accounts for fuel-wall impingement, which usually occurs in case of low-medium injection pressure or advanced injection timing. This feature is fundamental to investigate a wide range of injection timing, as that applied for advanced combustion concepts (i.e. Premixed Charge Compression Ignition (PCCI)). In the model the jet core is divided into many parcels in order to describe the thermal gradient and the chemical composition within the combustion chamber, fundamental to estimate NO_x and soot emissions. The impingement of the spray on cylinder walls is modeled by a zero-dimensional approach simulating dynamics and evaporation of the fuel film with two different semi-empirical models. Model parameters identification and validation have been carried out vs. experimental data measured at the engine test stand on a light-duty Diesel engine, equipped with a Magneti Marelli prototype medium pressure injection system based on a solenoid direct actuation injector.