Comparing Optimization Methods for Prechamber Spark Plug Operations in Natural Gas Engines using CFD-Simulation

One of the challenges engineering has to face today is environmental sustainability. It means restrictions of emissions’ standards, as well as consumption reduction to save resources. Moreover, the trend to produce electric power by means of renewable sources (highly aleatory), implies the need for alternative power sources to supply the grid during power lack phases. For this purpose, natural gas fed internal combustion engines have been used in the past. Today, prechamber technology is bringing gas engines back in fashion. To keep the mixture very lean as to reduce fuel consumption is not trivial, as combustion could be incomplete, and the engine could suffer from knock and low power. Installing a prechamber means to start the combustion in that narrow volume, causing a dramatic increase in pressure. Thanks to the throttling effect between preand main chamber, burnt gases jets are quickly diffused into the cylinder, and being the jets turbulent, they provoke the proper burning of the mixture. Prechamber geometry despite very small now turns out to be as important as the whole cylinder one, as every single hole and surface is responsible for flame propagation. The purpose of this work is to understand which part of the geometry design process is crucial, and to find the best solution comparing several prechamber and cylinder geometries. The engine studied is not equipped with fuel injector inside the prechamber (passive prechamber). The latter acts only as a concentrating factor for combustion, and mixture is not stoichiometric there.