Model Development of a CNG Active Pre-chamber Fuel Injection System

Natural gas as an internal combustion engine fuel is taking a predominant role as a mid-term solution to pollution due to combustion driven human activities both in the energy and transport sectors. Engine researchers and manufacturers are in the process of investigating and improving strategies that decrease emissions and fuel consumption, without compromising engine performance and efficiency; active pre-chamber configurations are to be accounted for as one of these. A relatively small amount of fuel (up to 10 % of the total fuel-energy requirement) is introduced in the confined volume of the pre-chamber and forms a close-to-stoichiometric mixture with fresh charge that is introduced from the main combustion chamber during the compression stroke. After spark-ignition the products of this early stage of combustion can ignite ultra-lean mixtures (with λ up to 2) through the Turbulent Jet Ignition mechanism, hence reducing fuel consumption as well as noxious emissions such as NOx. Mixture formation in the pre-chamber has an important role in driving the combustion process that takes place therein. Prediction and control of mixture composition and distribution become necessary in view of an optimal operation, therefore precise control of the timings and procedures of fuel introduction in the pre-chamber is necessary. In this work 0D and 1D modelling in Matlab-Simulink environment was coupled and integrated with computer-aided design in order to establish geometry and fluid-dynamic parameters of the injection system components as well as characterizing flow along the route to the pre-chamber. This preliminary study was aimed at the layout design of the injection system. The resulting model is the starting point for the design of a Real-Time control system to employ during engine operation, in view of realistic on-road heavy-duty applications.