Most of the phenomena that occur during the high pressure cycle of a spark ignition engine are highly influenced by the gas temperature, turbulence intensity and turbulence length scale inside the cylinder. For a pre chamber gas engine, the small volume and the high surface-to-volume ratio of the pre chamber increases the relative significance of the gas-to-wall heat losses, the early flame kernel development and the wall induced quenching; all of these phenomena are associated up to a certain extent with the turbulence and temperature field inside the pre chamber. While three-dimensional (3D) computational fluid dynamics (CFD) simulations can capture complex phenomena inside the pre chamber with high accuracy, they have high computational cost. Quasi dimensional models, on the contrary, provide a computationally inexpensive alternative for simulating multiple operating conditions as well as different geometries.
This article presents a novel model for the prediction of the temperature and pressure traces as well as the evolution of the mean and turbulence flow field in the pre chamber of a gas engine. Existing turbulence and gas-to-wall heat transfer models initially developed for spark ignition and diesel engines were studied for their capability to predict phenomena occurring inside the pre chamber. The zero dimensional model derived comprises two main novelties; namely, I) refinements of the existing models have been performed based on phenomenological observations specifically for the pre chamber, in order to introduce more accuracy to the overall model; II) extensive validation of the proposed submodels was conducted using results from detailed 3D CFD simulations of an instrumented research Liebherr gas engine in various operating points and different pre chamber geometries.