A zero-dimensional global conservation model to determine non-ideal nozzle conditions for gas injections

Abstract

To reduce computation times of simulations involving gas fueled internal combustion engines (ICEs), a model is developed that determines non-ideal nozzle exit conditions to spare expensive simulations of internal injector flows. The model, to which we will refer as the Global Conservation Model (GCM), computes nozzle exit values based on reservoir conditions, and a discharge and momentum coefficient. These coefficients can be obtained via common flow bench experiments or a validated numerical simulation setup. Furthermore, it allows to use real gas thermodynamics which is often needed for ICE applications. The model is validated for three commonly used injector types, injection pressures up to 300 bar, subsonic and choked injections, and at flow bench and engine conditions using numerical simulations. If real gas thermodynamics is applied, differences with the simulated nozzle conditions are typically within 1.5% uncertainty, which is within the typical range of experimental momentum flow measurements found in literature. Differences in mass and momentum flow obtained by the numerical simulations between flow bench and engine conditions are negligible, indicating that flow bench measurements can be applied to engine conditions. Once an injector is characterized for mass and momentum flow, applying the GCM can reduce computation times by more than a factor 8, while accurately simulating the spatial and temporal jet development. With the reduction in computation time, the GCM reduces costs associated with numerical simulations and accelerates research and design of efficient and low-emission gas fueled ICEs.