Numerical Analysis of Methane Direct Injection in a Single-cylinder 250 cm3 Spark Ignition Engine

The paper shows the results of the numerical tasks of a study aimed to evaluate the potential of low-pressure (< 20 bar) direct injection systems for internal combustion engines fed with gaseous fuels. Starting from the geometry of a low-cost commercial injector already available for GDI uses, a 2D axisymmetric CFD analyses is performed to assess the influence of injection pressure and valve and seat-valve profiles on jet characteristics, methane-air mixing, and charge distribution at ignition time. Then 3D simulations for the motorcycle single cylinder test-engine are carried out considering as much as possible combustion chamber details and realistic boundary conditions. Although it is possible identifying which operating and geometrical details of injection system are able to support complete mixture homogeneity, this study shows tremendous difficulties, in case of gaseous fuels, to realise satisfactory stratification charges that would be required to obtain satisfactory performance at partial loads.