Simulation of injection and combustion processes in 4-stroke spark ignition engine with CNG direct injection

The paper presents results of simulation conducted as afirst step of 4-stroke spark ignition experimental engine testing. The simulations were performed in a KIVA-3Vsoftware, which is intended to carry out a 3-D simulations of engine's processes. The source code of the software has been modified in order to apply it for gas injection. Original version of the software has been designedto simulate liquid fuel injection only. The simulation of direct CNG injection and combustion has been done for stratified and homogenous modes in order to check the assumed injection, ignition and charging parameters. Important assumption is that the injector had only one nozzle with flow area equal to 2 mm2. Two different cases of fuel direct injection for stratified charge have been analysed. In the first case fuel jet was almost vertical. In the other one fuel jet was nearly horizontal. Further testing has been performed using one-cylinder motorcycle 4-stroke SUZUKI DR-Z400S engine adapted to CNG fuelling. Such an engine has a suitable high compression ratio for CNG fuelling. The simulation has confirmed assumed parameters and has shown that one nozzle injector doesn't provide required fuel stream dissipation and piston crown modification is needed to direct fuel stream in spark plug area. However doing simulation requires some effort this example has shown than this is very important step before conducting experimental tests which provides crucial information and helps to avoid expensive mistakes which can be made during experimental engine preparation.