Diesel engine CFD simulations: Influence of fuel variability on ignition delay

Abstract

The modeling of fuel chemistry within computational fluid dynamics (CFD) simulations of diesel and other compression ignition engines is important because fuel composition and properties can significantly influence engine performance. Modern detailed chemical mechanisms containing detailed descriptions of the elementary reaction pathways can provide predictive modeling of fuel chemistry; however, they are generally far too computationally expensive for use in CFD and computational engine design and are often only available for single fuel components or simple component mixtures. We present CFD simulations of diesel engine combustion, focused on the prediction of ignition timing, carried out using an unsteady RANS approach with available sub-models to describe spray breakup physics. Chemistry is treated with a reduced global reaction model that incorporates parameters to describe fuel variability and can represent a range of real diesel and jet fuels. The derived cetane number (DCN) is used as a metric for fuel reactivity and a means to define rate parameters within the global reaction model. CFD simulations are compared to experiments from a light-duty single-cylinder diesel engine and show good agreement for ignition timing and the influence of fuel variability on ignition timing. Sensitivity analyses illustrate the relative importance of fuel variation as well as the importance of sub-models used to treat turbulence and spray breakup.